cosmopolitan/third_party/stb/stb_image.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/bits/bits.h"
#include "libc/calls/calls.h"
#include "libc/fmt/conv.h"
#include "libc/limits.h"
#include "libc/log/gdb.h"
#include "libc/log/log.h"
#include "libc/macros.internal.h"
#include "libc/math.h"
#include "libc/mem/mem.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/runtime/runtime.h"
#include "libc/stdio/stdio.h"
#include "libc/str/str.h"
#include "libc/x/x.h"
#include "third_party/stb/internal.h"
#include "third_party/stb/stb_image.h"

#define ROL(w, k) ((w) << (k) | CheckUnsigned(w) >> (sizeof(w) * 8 - (k)))

asm(".ident\t\"\\n\\n\
stb_image (Public Domain)\\n\
Credit: Sean Barrett, et al.\\n\
http://nothings.org/stb\"");

#ifndef STBI_REALLOC_SIZED
#define STBI_REALLOC_SIZED(p, oldsz, newsz) realloc(p, newsz)
#endif

// stbi__context structure is our basic context used by all images, so it
// contains all the IO context, plus some basic image information
typedef struct {
  uint32_t img_x, img_y;
  int img_n, img_out_n;
  stbi_io_callbacks io;
  void *io_user_data;
  int read_from_callbacks;
  int buflen;
  unsigned char buffer_start[128];
  unsigned char *img_buffer, *img_buffer_end;
  unsigned char *img_buffer_original, *img_buffer_original_end;
} stbi__context;

static const unsigned char kPngSig[8] = {137, 80, 78, 71, 13, 10, 26, 10};

static void stbi__refill_buffer(stbi__context *s);

// initialize a memory-decode context
static void stbi__start_mem(stbi__context *s, unsigned char const *buffer,
                            int len) {
  s->io.read = NULL;
  s->read_from_callbacks = 0;
  s->img_buffer = s->img_buffer_original = (unsigned char *)buffer;
  s->img_buffer_end = s->img_buffer_original_end =
      (unsigned char *)buffer + len;
}

// initialize a callback-based context
static void stbi__start_callbacks(stbi__context *s, stbi_io_callbacks *c,
                                  void *user) {
  s->io = *c;
  s->io_user_data = user;
  s->buflen = sizeof(s->buffer_start);
  s->read_from_callbacks = 1;
  s->img_buffer_original = s->buffer_start;
  stbi__refill_buffer(s);
  s->img_buffer_original_end = s->img_buffer_end;
}

static int stbi__stdio_read(void *user, char *data, int size) {
  return fread(data, 1, size, user);
}

static void stbi__stdio_skip(void *user, int n) {
  fseek(user, n, SEEK_CUR);
}

static int stbi__stdio_eof(void *user) {
  return feof(user);
}

static stbi_io_callbacks stbi__stdio_callbacks = {
    stbi__stdio_read,
    stbi__stdio_skip,
    stbi__stdio_eof,
};

static void stbi__start_file(stbi__context *s, FILE *f) {
  stbi__start_callbacks(s, &stbi__stdio_callbacks, (void *)f);
}

static void stbi__rewind(stbi__context *s) {
  // conceptually rewind SHOULD rewind to the beginning of the stream,
  // but we just rewind to the beginning of the initial buffer, because
  // we only use it after doing 'test', which only ever looks at at most 92
  // bytes
  s->img_buffer = s->img_buffer_original;
  s->img_buffer_end = s->img_buffer_original_end;
}

enum { STBI_ORDER_RGB, STBI_ORDER_BGR };

typedef struct {
  int bits_per_channel;
  int num_channels;
} stbi__result_info;

static int stbi__jpeg_test(stbi__context *);
static void *stbi__jpeg_load(stbi__context *, int *, int *, int *, int,
                             stbi__result_info *);
static int stbi__jpeg_info(stbi__context *, int *, int *, int *);
static int stbi__png_test(stbi__context *);
static void *stbi__png_load(stbi__context *, int *, int *, int *, int,
                            stbi__result_info *);
static int stbi__png_info(stbi__context *, int *, int *, int *);
static int stbi__png_is16(stbi__context *);
static int stbi__gif_test(stbi__context *);
static void *stbi__gif_load(stbi__context *, int *, int *, int *, int,
                            stbi__result_info *);
static void *stbi__load_gif_main(stbi__context *, int **, int *, int *, int *,
                                 int *, int);
static int stbi__gif_info(stbi__context *, int *, int *, int *);
static int stbi__pnm_test(stbi__context *);
static void *stbi__pnm_load(stbi__context *, int *, int *, int *, int,
                            stbi__result_info *);
static int stbi__pnm_info(stbi__context *, int *, int *, int *);

static const char *stbi__g_failure_reason;

static int stbi__vertically_flip_on_load = 0;

const char *stbi_failure_reason(void) {
  return stbi__g_failure_reason;
}

static int stbi__err(const char *specific_details,
                     const char *general_details) {
  /* DebugBreak(); */
  /* WARNF("%s: %s", general_details, specific_details); */
  stbi__g_failure_reason = general_details;
  return 0;
}

// stb_image uses ints pervasively, including for offset calculations.
// therefore the largest decoded image size we can support with the
// current code, even on 64-bit targets, is INT_MAX. this is not a
// significant limitation for the intended use case.
//
// we do, however, need to make sure our size calculations don't
// overflow. hence a few helper functions for size calculations that
// multiply integers together, making sure that they're non-negative
// and no overflow occurs.

// return 1 if the sum is valid, 0 on overflow.
// negative terms are considered invalid.
static int stbi__addsizes_valid(int a, int b) {
  if (b < 0) return 0;
  // now 0 <= b <= INT_MAX, hence also
  // 0 <= INT_MAX - b <= INTMAX.
  // And "a + b <= INT_MAX" (which might overflow) is the
  // same as a <= INT_MAX - b (no overflow)
  return a <= INT_MAX - b;
}

// returns 1 if the product is valid, 0 on overflow.
// negative factors are considered invalid.
static int stbi__mul2sizes_valid(int a, int b) {
  if (a < 0 || b < 0) return 0;
  if (b == 0) return 1;  // mul-by-0 is always safe
  // portable way to check for no overflows in a*b
  return a <= INT_MAX / b;
}

// returns 1 if "a*b + add" has no negative terms/factors and doesn't overflow
static int stbi__mad2sizes_valid(int a, int b, int add) {
  return stbi__mul2sizes_valid(a, b) && stbi__addsizes_valid(a * b, add);
}

// returns 1 if "a*b*c + add" has no negative terms/factors and doesn't overflow
static int stbi__mad3sizes_valid(int a, int b, int c, int add) {
  return stbi__mul2sizes_valid(a, b) && stbi__mul2sizes_valid(a * b, c) &&
         stbi__addsizes_valid(a * b * c, add);
}

// mallocs with size overflow checking
static void *stbi__malloc_mad2(int a, int b, int add) {
  if (!stbi__mad2sizes_valid(a, b, add)) return NULL;
  return xmalloc(a * b + add);
}

static void *stbi__malloc_mad3(int a, int b, int c, int add) {
  if (!stbi__mad3sizes_valid(a, b, c, add)) return NULL;
  return xmalloc(a * b * c + add);
}

#define stbi__errpf(x, y) \
  ({                      \
    stbi__err(x, y);      \
    NULL;                 \
  })

#define stbi__errpuc(x, y) \
  ({                       \
    stbi__err(x, y);       \
    NULL;                  \
  })

void stbi_image_free(void *retval_from_stbi_load) {
  free(retval_from_stbi_load);
}

void stbi_set_flip_vertically_on_load(int flag_true_if_should_flip) {
  stbi__vertically_flip_on_load = flag_true_if_should_flip;
}

static void *stbi__load_main(stbi__context *s, int *x, int *y, int *comp,
                             int req_comp, stbi__result_info *ri, int bpc) {
  bzero(ri, sizeof(*ri));
  ri->bits_per_channel = 8;
  ri->num_channels = 0;
#ifndef STBI_NO_JPEG
  if (stbi__jpeg_test(s)) return stbi__jpeg_load(s, x, y, comp, req_comp, ri);
#endif
#ifndef STBI_NO_PNG
  if (stbi__png_test(s)) return stbi__png_load(s, x, y, comp, req_comp, ri);
#endif
#ifndef STBI_NO_GIF
  if (stbi__gif_test(s)) return stbi__gif_load(s, x, y, comp, req_comp, ri);
#endif
#ifndef STBI_NO_PNM
  if (stbi__pnm_test(s)) return stbi__pnm_load(s, x, y, comp, req_comp, ri);
#endif
  return stbi__errpuc("unknown image type",
                      "Image not of any known type, or corrupt");
}

unsigned char *stbi__convert_16_to_8(uint16_t *orig, int w, int h,
                                     int channels) {
  int i;
  int img_len = w * h * channels;
  unsigned char *reduced = xmalloc(img_len);
  for (i = 0; i < img_len; ++i) {
    // top half of each byte is sufficient
    // approx of 16->8 bit scaling
    reduced[i] = (orig[i] >> 8) & 0xff;
  }
  free(orig);
  return reduced;
}

uint16_t *stbi__convert_8_to_16(unsigned char *orig, int w, int h,
                                int channels) {
  int i;
  int img_len = w * h * channels;
  uint16_t *enlarged = xmalloc(img_len * 2);
  for (i = 0; i < img_len; ++i) {
    // replicate to high and low byte, maps 0->0, 255->0xffff
    enlarged[i] = (uint16_t)((orig[i] << 8) + orig[i]);
  }
  free(orig);
  return enlarged;
}

static void stbi__vertical_flip(void *image, int w, int h,
                                int bytes_per_pixel) {
  int row;
  size_t bytes_per_row, bytes_left, bytes_copy;
  unsigned char *row0, *row1, *bytes, temp[2048];
  bytes = image;
  bytes_per_row = bytes_per_pixel * w;
  for (row = 0; row < (h >> 1); row++) {
    row0 = bytes + row * bytes_per_row;
    row1 = bytes + (h - row - 1) * bytes_per_row;
    // swap row0 with row1
    bytes_left = bytes_per_row;
    while (bytes_left) {
      bytes_copy = bytes_left < sizeof(temp) ? bytes_left : sizeof(temp);
      memcpy(temp, row0, bytes_copy);
      memcpy(row0, row1, bytes_copy);
      memcpy(row1, temp, bytes_copy);
      row0 += bytes_copy;
      row1 += bytes_copy;
      bytes_left -= bytes_copy;
    }
  }
}

static void stbi__vertical_flip_slices(void *image, int w, int h, int z,
                                       int bytes_per_pixel) {
  unsigned char *bytes;
  int slice, slice_size;
  bytes = image;
  slice_size = w * h * bytes_per_pixel;
  for (slice = 0; slice < z; ++slice) {
    stbi__vertical_flip(bytes, w, h, bytes_per_pixel);
    bytes += slice_size;
  }
}

static unsigned char *stbi__load_and_postprocess_8bit(stbi__context *s, int *x,
                                                      int *y, int *comp,
                                                      int req_comp) {
  void *result;
  stbi__result_info ri;
  result = stbi__load_main(s, x, y, comp, req_comp, &ri, 8);
  if (result == NULL) return NULL;
  if (ri.bits_per_channel != 8) {
    assert(ri.bits_per_channel == 16);
    result =
        stbi__convert_16_to_8(result, *x, *y, req_comp == 0 ? *comp : req_comp);
    ri.bits_per_channel = 8;
  }
  // @TODO: move stbi__convert_format to here
  if (stbi__vertically_flip_on_load) {
    int channels = req_comp ? req_comp : *comp;
    stbi__vertical_flip(result, *x, *y, channels * sizeof(unsigned char));
  }
  return (unsigned char *)result;
}

static uint16_t *stbi__load_and_postprocess_16bit(stbi__context *s, int *x,
                                                  int *y, int *comp,
                                                  int req_comp) {
  stbi__result_info ri;
  void *result = stbi__load_main(s, x, y, comp, req_comp, &ri, 16);
  if (result == NULL) return NULL;
  if (ri.bits_per_channel != 16) {
    assert(ri.bits_per_channel == 8);
    result = stbi__convert_8_to_16((unsigned char *)result, *x, *y,
                                   req_comp == 0 ? *comp : req_comp);
    ri.bits_per_channel = 16;
  }
  // @TODO: move stbi__convert_format16 to here
  // @TODO: special case RGB-to-Y (and RGBA-to-YA) for 8-bit-to-16-bit case to
  // keep more precision
  if (stbi__vertically_flip_on_load) {
    int channels = req_comp ? req_comp : *comp;
    stbi__vertical_flip(result, *x, *y, channels * sizeof(uint16_t));
  }

  return (uint16_t *)result;
}

static FILE *stbi__fopen(char const *filename, char const *mode) {
  return fopen(filename, mode);
}

unsigned char *stbi_load(char const *filename, int *x, int *y, int *comp,
                         int req_comp) {
  FILE *f = stbi__fopen(filename, "rb");
  unsigned char *result;
  if (!f) return stbi__errpuc("can't fopen", "Unable to open file");
  result = stbi_load_from_file(f, x, y, comp, req_comp);
  fclose(f);
  return result;
}

unsigned char *stbi_load_from_file(FILE *f, int *x, int *y, int *comp,
                                   int req_comp) {
  unsigned char *result;
  stbi__context s;
  stbi__start_file(&s, f);
  result = stbi__load_and_postprocess_8bit(&s, x, y, comp, req_comp);
  if (result) {
    // need to 'unget' all the characters in the IO buffer
    fseek(f, -(int)(s.img_buffer_end - s.img_buffer), SEEK_CUR);
  }
  return result;
}

uint16_t *stbi_load_from_file_16(FILE *f, int *x, int *y, int *comp,
                                 int req_comp) {
  uint16_t *result;
  stbi__context s;
  stbi__start_file(&s, f);
  result = stbi__load_and_postprocess_16bit(&s, x, y, comp, req_comp);
  if (result) {
    // need to 'unget' all the characters in the IO buffer
    fseek(f, -(int)(s.img_buffer_end - s.img_buffer), SEEK_CUR);
  }
  return result;
}

unsigned short *stbi_load_16(char const *filename, int *x, int *y, int *comp,
                             int req_comp) {
  FILE *f = stbi__fopen(filename, "rb");
  uint16_t *result;
  if (!f) return stbi__errpuc("can't fopen", "Unable to open file");
  result = stbi_load_from_file_16(f, x, y, comp, req_comp);
  fclose(f);
  return result;
}

unsigned short *stbi_load_16_from_memory(unsigned char const *buffer, int len,
                                         int *x, int *y, int *channels_in_file,
                                         int desired_channels) {
  stbi__context s;
  stbi__start_mem(&s, buffer, len);
  return stbi__load_and_postprocess_16bit(&s, x, y, channels_in_file,
                                          desired_channels);
}

unsigned short *stbi_load_16_from_callbacks(stbi_io_callbacks const *clbk,
                                            void *user, int *x, int *y,
                                            int *channels_in_file,
                                            int desired_channels) {
  stbi__context s;
  stbi__start_callbacks(&s, (stbi_io_callbacks *)clbk, user);
  return stbi__load_and_postprocess_16bit(&s, x, y, channels_in_file,
                                          desired_channels);
}

unsigned char *stbi_load_from_memory(unsigned char const *buffer, int len,
                                     int *x, int *y, int *comp, int req_comp) {
  stbi__context s;
  stbi__start_mem(&s, buffer, len);
  return stbi__load_and_postprocess_8bit(&s, x, y, comp, req_comp);
}

unsigned char *stbi_load_from_callbacks(stbi_io_callbacks const *clbk,
                                        void *user, int *x, int *y, int *comp,
                                        int req_comp) {
  stbi__context s;
  stbi__start_callbacks(&s, (stbi_io_callbacks *)clbk, user);
  return stbi__load_and_postprocess_8bit(&s, x, y, comp, req_comp);
}

unsigned char *stbi_load_gif_from_memory(unsigned char const *buffer, int len,
                                         int **delays, int *x, int *y, int *z,
                                         int *comp, int req_comp) {
  unsigned char *result;
  stbi__context s;
  stbi__start_mem(&s, buffer, len);
  result =
      (unsigned char *)stbi__load_gif_main(&s, delays, x, y, z, comp, req_comp);
  if (stbi__vertically_flip_on_load) {
    stbi__vertical_flip_slices(result, *x, *y, *z, *comp);
  }
  return result;
}

enum { STBI__SCAN_load = 0, STBI__SCAN_type, STBI__SCAN_header };

static void stbi__refill_buffer(stbi__context *s) {
  int n = (s->io.read)(s->io_user_data, (char *)s->buffer_start, s->buflen);
  if (n == 0) {
    // at end of file, treat same as if from memory, but need to handle case
    // where s->img_buffer isn't pointing to safe memory, e.g. 0-byte file
    s->read_from_callbacks = 0;
    s->img_buffer = s->buffer_start;
    s->img_buffer_end = s->buffer_start + 1;
    *s->img_buffer = 0;
  } else {
    s->img_buffer = s->buffer_start;
    s->img_buffer_end = s->buffer_start + n;
  }
}

forceinline unsigned char stbi__get8(stbi__context *s) {
  if (s->img_buffer < s->img_buffer_end) return *s->img_buffer++;
  if (s->read_from_callbacks) {
    stbi__refill_buffer(s);
    return *s->img_buffer++;
  }
  return 0;
}

forceinline int stbi__at_eof(stbi__context *s) {
  if (s->io.read) {
    if (!(s->io.eof)(s->io_user_data)) return 0;
    // if feof() is true, check if buffer = end
    // special case: we've only got the special 0 character at the end
    if (s->read_from_callbacks == 0) return 1;
  }

  return s->img_buffer >= s->img_buffer_end;
}

static void stbi__skip(stbi__context *s, int n) {
  if (n < 0) {
    s->img_buffer = s->img_buffer_end;
    return;
  }
  if (s->io.read) {
    int blen = (int)(s->img_buffer_end - s->img_buffer);
    if (blen < n) {
      s->img_buffer = s->img_buffer_end;
      (s->io.skip)(s->io_user_data, n - blen);
      return;
    }
  }
  s->img_buffer += n;
}

static int stbi__getn(stbi__context *s, unsigned char *buffer, int n) {
  if (s->io.read) {
    int blen = (int)(s->img_buffer_end - s->img_buffer);
    if (blen < n) {
      int res, count;
      memcpy(buffer, s->img_buffer, blen);
      count = (s->io.read)(s->io_user_data, (char *)buffer + blen, n - blen);
      res = (count == (n - blen));
      s->img_buffer = s->img_buffer_end;
      return res;
    }
  }
  if (s->img_buffer + n <= s->img_buffer_end) {
    memcpy(buffer, s->img_buffer, n);
    s->img_buffer += n;
    return 1;
  } else {
    return 0;
  }
}

static int stbi__get16le(stbi__context *s) {
  int z = stbi__get8(s);
  return z + (stbi__get8(s) << 8);
}

static int stbi__get16be(stbi__context *s) {
  int z = stbi__get8(s);
  return (z << 8) + stbi__get8(s);
}

static uint32_t stbi__get32be(stbi__context *s) {
  uint32_t z = stbi__get16be(s);
  return (z << 16) + stbi__get16be(s);
}

#define STBI__BYTECAST(x) \
  ((unsigned char)((x)&255))  // truncate int to byte without warnings

//////////////////////////////////////////////////////////////////////////////
//
//  generic converter from built-in img_n to req_comp
//    individual types do this automatically as much as possible (e.g. jpeg
//    does all cases internally since it needs to colorspace convert anyway,
//    and it never has alpha, so very few cases ). png can automatically
//    interleave an alpha=255 channel, but falls back to this for other cases
//
//  assume data buffer is malloced, so malloc a new one and free that one
//  only failure mode is malloc failing

static unsigned char stbi__compute_y(int r, int g, int b) {
  return (unsigned char)(((r * 77) + (g * 150) + (29 * b)) >> 8);
}

static unsigned char *stbi__convert_format(unsigned char *data, int img_n,
                                           int req_comp, unsigned int x,
                                           unsigned int y) {
  int i, j;
  unsigned char *good, *src, *dest;
  if (req_comp == img_n) return data;
  assert(req_comp >= 1 && req_comp <= 4);
  good = stbi__malloc_mad3(req_comp, x, y, 0);
  for (j = 0; j < (int)y; ++j) {
    src = data + j * x * img_n;
    dest = good + j * x * req_comp;
#define STBI__COMBO(a, b) ((a)*8 + (b))
#define STBI__CASE(a, b)  \
  case STBI__COMBO(a, b): \
    for (i = x - 1; i >= 0; --i, src += a, dest += b)
    // convert source image with img_n components to one with req_comp
    // components; avoid switch per pixel, so use switch per scanline and
    // massive macros
    switch (STBI__COMBO(img_n, req_comp)) {
      STBI__CASE(1, 2) {
        dest[0] = src[0];
        dest[1] = 255;
      }
      break;
      STBI__CASE(1, 3) {
        dest[0] = dest[1] = dest[2] = src[0];
      }
      break;
      STBI__CASE(1, 4) {
        dest[0] = dest[1] = dest[2] = src[0];
        dest[3] = 255;
      }
      break;
      STBI__CASE(2, 1) {
        dest[0] = src[0];
      }
      break;
      STBI__CASE(2, 3) {
        dest[0] = dest[1] = dest[2] = src[0];
      }
      break;
      STBI__CASE(2, 4) {
        dest[0] = dest[1] = dest[2] = src[0];
        dest[3] = src[1];
      }
      break;
      STBI__CASE(3, 4) {
        dest[0] = src[0];
        dest[1] = src[1];
        dest[2] = src[2];
        dest[3] = 255;
      }
      break;
      STBI__CASE(3, 1) {
        dest[0] = stbi__compute_y(src[0], src[1], src[2]);
      }
      break;
      STBI__CASE(3, 2) {
        dest[0] = stbi__compute_y(src[0], src[1], src[2]);
        dest[1] = 255;
      }
      break;
      STBI__CASE(4, 1) {
        dest[0] = stbi__compute_y(src[0], src[1], src[2]);
      }
      break;
      STBI__CASE(4, 2) {
        dest[0] = stbi__compute_y(src[0], src[1], src[2]);
        dest[1] = src[3];
      }
      break;
      STBI__CASE(4, 3) {
        dest[0] = src[0];
        dest[1] = src[1];
        dest[2] = src[2];
      }
      break;
      default:
        assert(0);
    }
#undef STBI__CASE
  }
  free(data);
  return good;
}

static uint16_t stbi__compute_y_16(int r, int g, int b) {
  return (uint16_t)(((r * 77) + (g * 150) + (29 * b)) >> 8);
}

static uint16_t *stbi__convert_format16(uint16_t *data, int img_n, int req_comp,
                                        unsigned int x, unsigned int y) {
  int i, j;
  uint16_t *good;

  if (req_comp == img_n) return data;
  assert(req_comp >= 1 && req_comp <= 4);

  good = xmalloc(req_comp * x * y * 2);

  for (j = 0; j < (int)y; ++j) {
    uint16_t *src = data + j * x * img_n;
    uint16_t *dest = good + j * x * req_comp;

#define STBI__COMBO(a, b) ((a)*8 + (b))
#define STBI__CASE(a, b)  \
  case STBI__COMBO(a, b): \
    for (i = x - 1; i >= 0; --i, src += a, dest += b)
    // convert source image with img_n components to one with req_comp
    // components; avoid switch per pixel, so use switch per scanline and
    // massive macros
    switch (STBI__COMBO(img_n, req_comp)) {
      STBI__CASE(1, 2) {
        dest[0] = src[0];
        dest[1] = 0xffff;
      }
      break;
      STBI__CASE(1, 3) {
        dest[0] = dest[1] = dest[2] = src[0];
      }
      break;
      STBI__CASE(1, 4) {
        dest[0] = dest[1] = dest[2] = src[0];
        dest[3] = 0xffff;
      }
      break;
      STBI__CASE(2, 1) {
        dest[0] = src[0];
      }
      break;
      STBI__CASE(2, 3) {
        dest[0] = dest[1] = dest[2] = src[0];
      }
      break;
      STBI__CASE(2, 4) {
        dest[0] = dest[1] = dest[2] = src[0];
        dest[3] = src[1];
      }
      break;
      STBI__CASE(3, 4) {
        dest[0] = src[0];
        dest[1] = src[1];
        dest[2] = src[2];
        dest[3] = 0xffff;
      }
      break;
      STBI__CASE(3, 1) {
        dest[0] = stbi__compute_y_16(src[0], src[1], src[2]);
      }
      break;
      STBI__CASE(3, 2) {
        dest[0] = stbi__compute_y_16(src[0], src[1], src[2]);
        dest[1] = 0xffff;
      }
      break;
      STBI__CASE(4, 1) {
        dest[0] = stbi__compute_y_16(src[0], src[1], src[2]);
      }
      break;
      STBI__CASE(4, 2) {
        dest[0] = stbi__compute_y_16(src[0], src[1], src[2]);
        dest[1] = src[3];
      }
      break;
      STBI__CASE(4, 3) {
        dest[0] = src[0];
        dest[1] = src[1];
        dest[2] = src[2];
      }
      break;
      default:
        assert(0);
    }
#undef STBI__CASE
  }

  free(data);
  return good;
}

//////////////////////////////////////////////////////////////////////////////
//
//  "baseline" JPEG/JFIF decoder
//
//    simple implementation
//      - doesn't support delayed output of y-dimension
//      - simple interface (only one output format: 8-bit interleaved RGB)
//      - doesn't try to recover corrupt jpegs
//      - doesn't allow partial loading, loading multiple at once
//      - still fast on x86 (copying globals into locals doesn't help x86)
//      - allocates lots of intermediate memory (full size of all components)
//        - non-interleaved case requires this anyway
//        - allows good upsampling (see next)
//    high-quality
//      - upsampled channels are bilinearly interpolated, even across blocks
//      - quality integer IDCT derived from IJG's 'slow'
//    performance
//      - fast huffman; reasonable integer IDCT
//      - some SIMD kernels for common paths on targets with SSE2/NEON
//      - uses a lot of intermediate memory, could cache poorly

// huffman decoding acceleration
#define FAST_BITS 9  // larger handles more cases; smaller stomps less cache

typedef struct {
  unsigned char fast[1 << FAST_BITS];
  // weirdly, repacking this into AoS is a 10% speed loss, instead of a win
  uint16_t code[256];
  unsigned char values[256];
  unsigned char size[257];
  unsigned int maxcode[18];
  int delta[17];  // old 'firstsymbol' - old 'firstcode'
} stbi__huffman;

typedef struct {
  stbi__context *s;
  stbi__huffman huff_dc[4];
  stbi__huffman huff_ac[4];
  uint16_t dequant[4][64];
  int16_t fast_ac[4][1 << FAST_BITS];

  // sizes for components, interleaved MCUs
  int img_h_max, img_v_max;
  int img_mcu_x, img_mcu_y;
  int img_mcu_w, img_mcu_h;

  // definition of jpeg image component
  struct {
    int id;
    int h, v;
    int tq;
    int hd, ha;
    int dc_pred;

    int x, y, w2, h2;
    unsigned char *data;
    unsigned char *linebuf;
    short *coeff;          // progressive only
    int coeff_w, coeff_h;  // number of 8x8 coefficient blocks
  } img_comp[4];

  uint32_t code_buffer;  // jpeg entropy-coded buffer
  int code_bits;         // number of valid bits
  unsigned char marker;  // marker seen while filling entropy buffer
  int nomore;            // flag if we saw a marker so must stop

  int progressive;
  int spec_start;
  int spec_end;
  int succ_high;
  int succ_low;
  int eob_run;
  int jfif;
  int app14_color_transform;  // Adobe APP14 tag
  int rgb;

  int scan_n, order[4];
  int restart_interval, todo;

  // kernels
  unsigned char *(*resample_row_hv_2_kernel)(unsigned char *out,
                                             unsigned char *in_near,
                                             unsigned char *in_far, int w,
                                             int hs);
} stbi__jpeg;

static int stbi__build_huffman(stbi__huffman *h, int *count) {
  int i, j, k = 0;
  unsigned int code;
  // build size list for each symbol (from JPEG spec)
  for (i = 0; i < 16; ++i)
    for (j = 0; j < count[i]; ++j) h->size[k++] = (unsigned char)(i + 1);
  h->size[k] = 0;

  // compute actual symbols (from jpeg spec)
  code = 0;
  k = 0;
  for (j = 1; j <= 16; ++j) {
    // compute delta to add to code to compute symbol id
    h->delta[j] = k - code;
    if (h->size[k] == j) {
      while (h->size[k] == j) h->code[k++] = (uint16_t)(code++);
      if (code - 1 >= (1u << j)) {
        return stbi__err("bad code lengths", "Corrupt JPEG");
      }
    }
    // compute largest code + 1 for this size, preshifted as needed later
    h->maxcode[j] = code << (16 - j);
    code <<= 1;
  }
  h->maxcode[j] = 0xffffffff;

  // build non-spec acceleration table; 255 is flag for not-accelerated
  memset(h->fast, 255, 1 << FAST_BITS);
  for (i = 0; i < k; ++i) {
    int s = h->size[i];
    if (s <= FAST_BITS) {
      int c = h->code[i] << (FAST_BITS - s);
      int m = 1 << (FAST_BITS - s);
      for (j = 0; j < m; ++j) {
        h->fast[c + j] = (unsigned char)i;
      }
    }
  }
  return 1;
}

// build a table that decodes both magnitude and value of small ACs in
// one go.
static void stbi__build_fast_ac(int16_t *fast_ac, stbi__huffman *h) {
  int i;
  for (i = 0; i < (1 << FAST_BITS); ++i) {
    unsigned char fast = h->fast[i];
    fast_ac[i] = 0;
    if (fast < 255) {
      int rs = h->values[fast];
      int run = (rs >> 4) & 15;
      int magbits = rs & 15;
      int len = h->size[fast];
      if (magbits && len + magbits <= FAST_BITS) {
        // magnitude code followed by receive_extend code
        int k = ((i << len) & ((1 << FAST_BITS) - 1)) >> (FAST_BITS - magbits);
        int m = 1 << (magbits - 1);
        if (k < m) k += (~0U << magbits) + 1;
        // if the result is small enough, we can fit it in fast_ac table
        if (k >= -128 && k <= 127)
          fast_ac[i] = (int16_t)((k * 256) + (run * 16) + (len + magbits));
      }
    }
  }
}

static void stbi__grow_buffer_unsafe(stbi__jpeg *j) {
  do {
    unsigned b = j->nomore ? 0 : stbi__get8(j->s);
    if (b == 0xff) {
      int c = stbi__get8(j->s);
      while (c == 0xff) c = stbi__get8(j->s);  // consume fill bytes
      if (c != 0) {
        j->marker = (unsigned char)c;
        j->nomore = 1;
        return;
      }
    }
    j->code_buffer |= b << (24 - j->code_bits);
    j->code_bits += 8;
  } while (j->code_bits <= 24);
}

// (1 << n) - 1
static const uint32_t stbi__bmask[17] = {0,    1,    3,     7,     15,   31,
                                         63,   127,  255,   511,   1023, 2047,
                                         4095, 8191, 16383, 32767, 65535};

// decode a jpeg huffman value from the bitstream
forceinline int stbi__jpeg_huff_decode(stbi__jpeg *j, stbi__huffman *h) {
  unsigned int temp;
  int c, k;

  if (j->code_bits < 16) stbi__grow_buffer_unsafe(j);

  // look at the top FAST_BITS and determine what symbol ID it is,
  // if the code is <= FAST_BITS
  c = (j->code_buffer >> (32 - FAST_BITS)) & ((1 << FAST_BITS) - 1);
  k = h->fast[c];
  if (k < 255) {
    int s = h->size[k];
    if (s > j->code_bits) return -1;
    j->code_buffer <<= s;
    j->code_bits -= s;
    return h->values[k];
  }

  // naive test is to shift the code_buffer down so k bits are
  // valid, then test against maxcode. To speed this up, we've
  // preshifted maxcode left so that it has (16-k) 0s at the
  // end; in other words, regardless of the number of bits, it
  // wants to be compared against something shifted to have 16;
  // that way we don't need to shift inside the loop.
  temp = j->code_buffer >> 16;
  for (k = FAST_BITS + 1;; ++k)
    if (temp < h->maxcode[k]) break;
  if (k == 17) {
    // error! code not found
    j->code_bits -= 16;
    return -1;
  }

  if (k > j->code_bits) return -1;

  // convert the huffman code to the symbol id
  c = ((j->code_buffer >> (32 - k)) & stbi__bmask[k]) + h->delta[k];
  assert((((j->code_buffer) >> (32 - h->size[c])) & stbi__bmask[h->size[c]]) ==
         h->code[c]);

  // convert the id to a symbol
  j->code_bits -= k;
  j->code_buffer <<= k;
  return h->values[c];
}

// bias[n] = (-1<<n) + 1
static const int stbi__jbias[16] = {0,     -1,    -3,     -7,    -15,   -31,
                                    -63,   -127,  -255,   -511,  -1023, -2047,
                                    -4095, -8191, -16383, -32767};

// combined JPEG 'receive' and JPEG 'extend', since baseline
// always extends everything it receives.
forceinline int stbi__extend_receive(stbi__jpeg *j, int n) {
  int sgn;
  unsigned int k;
  // TODO(jart): what is this
  if (j->code_bits < n) stbi__grow_buffer_unsafe(j);
  sgn = (int32_t)j->code_buffer >> 31;  // sign bit is always in MSB
  k = ROL(j->code_buffer, n);
  assert(n >= 0 && n < (int)(sizeof(stbi__bmask) / sizeof(*stbi__bmask)));
  j->code_buffer = k & ~stbi__bmask[n];
  k &= stbi__bmask[n];
  j->code_bits -= n;
  return k + (stbi__jbias[n] & ~sgn);
}

// get some unsigned bits
forceinline int stbi__jpeg_get_bits(stbi__jpeg *j, int n) {
  unsigned int k;
  if (j->code_bits < n) stbi__grow_buffer_unsafe(j);
  k = ROL(j->code_buffer, n);
  j->code_buffer = k & ~stbi__bmask[n];
  k &= stbi__bmask[n];
  j->code_bits -= n;
  return k;
}

forceinline int stbi__jpeg_get_bit(stbi__jpeg *j) {
  unsigned int k;
  if (j->code_bits < 1) stbi__grow_buffer_unsafe(j);
  k = j->code_buffer;
  j->code_buffer <<= 1;
  --j->code_bits;
  return k & 0x80000000;
}

// given a value that's at position X in the zigzag stream,
// where does it appear in the 8x8 matrix coded as row-major?
static const unsigned char stbi__jpeg_dezigzag[64 + 15] = {
    0, 1, 8, 16, 9, 2, 3, 10, 17, 24, 32, 25, 18, 11, 4, 5, 12, 19, 26, 33, 40,
    48, 41, 34, 27, 20, 13, 6, 7, 14, 21, 28, 35, 42, 49, 56, 57, 50, 43, 36,
    29, 22, 15, 23, 30, 37, 44, 51, 58, 59, 52, 45, 38, 31, 39, 46, 53, 60, 61,
    54, 47, 55, 62, 63,
    // let corrupt input sample past end
    63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63};

// decode one 64-entry block
static optimizespeed int stbi__jpeg_decode_block(stbi__jpeg *j, short data[64],
                                                 stbi__huffman *hdc,
                                                 stbi__huffman *hac,
                                                 int16_t *fac, int b,
                                                 uint16_t *dequant) {
  unsigned int zig;
  int diff, dc, k, t, c, r, s, rs;
  if (j->code_bits < 16) stbi__grow_buffer_unsafe(j);
  t = stbi__jpeg_huff_decode(j, hdc);
  if (t < 0) return stbi__err("bad huffman code", "Corrupt JPEG");
  // 0 all the ac values now so we can do it 32-bits at a time
  bzero(data, 64 * sizeof(data[0]));
  diff = t ? stbi__extend_receive(j, t) : 0;
  dc = j->img_comp[b].dc_pred + diff;
  j->img_comp[b].dc_pred = dc;
  data[0] = (short)(dc * dequant[0]);
  // decode AC components, see JPEG spec
  k = 1;
  do {
    if (j->code_bits < 16) stbi__grow_buffer_unsafe(j);
    c = (j->code_buffer >> (32 - FAST_BITS)) & ((1 << FAST_BITS) - 1);
    r = fac[c];
    if (r) {               // fast-AC path
      k += (r >> 4) & 15;  // run
      s = r & 15;          // combined length
      j->code_buffer <<= s;
      j->code_bits -= s;
      // decode into unzigzag'd location
      zig = stbi__jpeg_dezigzag[k++];
      data[zig] = (short)((r >> 8) * dequant[zig]);
    } else {
      rs = stbi__jpeg_huff_decode(j, hac);
      if (rs < 0) return stbi__err("bad huffman code", "Corrupt JPEG");
      s = rs & 15;
      r = rs >> 4;
      if (s == 0) {
        if (rs != 0xf0) break;  // end block
        k += 16;
      } else {
        k += r;
        // decode into unzigzag'd location
        zig = stbi__jpeg_dezigzag[k++];
        data[zig] = (short)(stbi__extend_receive(j, s) * dequant[zig]);
      }
    }
  } while (k < 64);
  return 1;
}

static int stbi__jpeg_decode_block_prog_dc(stbi__jpeg *j, short data[64],
                                           stbi__huffman *hdc, int b) {
  int t;
  short s;
  int diff, dc;
  if (j->spec_end != 0) {
    return stbi__err("can't merge dc and ac", "Corrupt JPEG");
  }
  if (j->code_bits < 16) stbi__grow_buffer_unsafe(j);
  if (j->succ_high == 0) {
    // first scan for DC coefficient, must be first
    bzero(data, 64 * sizeof(data[0]));  // 0 all the ac values now
    t = stbi__jpeg_huff_decode(j, hdc);
    diff = t ? stbi__extend_receive(j, t) : 0;
    dc = j->img_comp[b].dc_pred + diff;
    j->img_comp[b].dc_pred = dc;
    s = dc;
    s *= 1u << j->succ_low;
    data[0] = s; /* (short)(dc << j->succ_low); */
  } else {
    // refinement scan for DC coefficient
    if (stbi__jpeg_get_bit(j)) data[0] += (short)(1 << j->succ_low);
  }
  return 1;
}

// @OPTIMIZE: store non-zigzagged during the decode passes,
// and only de-zigzag when dequantizing
static int stbi__jpeg_decode_block_prog_ac(stbi__jpeg *j, short data[64],
                                           stbi__huffman *hac, int16_t *fac) {
  short bit;
  unsigned zig;
  int k, c, r, s, rs, shift;
  if (j->spec_start == 0) {
    return stbi__err("can't merge dc and ac", "Corrupt JPEG");
  }
  if (j->succ_high == 0) {
    shift = j->succ_low;
    if (j->eob_run) {
      --j->eob_run;
      return 1;
    }
    k = j->spec_start;
    do {
      if (j->code_bits < 16) stbi__grow_buffer_unsafe(j);
      c = (j->code_buffer >> (32 - FAST_BITS)) & ((1 << FAST_BITS) - 1);
      r = fac[c];
      if (r) {               // fast-AC path
        k += (r >> 4) & 15;  // run
        s = r & 15;          // combined length
        j->code_buffer <<= s;
        j->code_bits -= s;
        zig = stbi__jpeg_dezigzag[k++];
        data[zig] = (r / 256) * (1u << shift);
      } else {
        rs = stbi__jpeg_huff_decode(j, hac);
        if (rs < 0) return stbi__err("bad huffman code", "Corrupt JPEG");
        s = rs & 15;
        r = rs >> 4;
        if (s == 0) {
          if (r < 15) {
            j->eob_run = (1 << r);
            if (r) j->eob_run += stbi__jpeg_get_bits(j, r);
            --j->eob_run;
            break;
          }
          k += 16;
        } else {
          k += r;
          zig = stbi__jpeg_dezigzag[k++];
          data[zig] = stbi__extend_receive(j, s) * (1u << shift);
        }
      }
    } while (k <= j->spec_end);
  } else {
    // refinement scan for these AC coefficients

    bit = (short)(1 << j->succ_low);

    if (j->eob_run) {
      --j->eob_run;
      for (k = j->spec_start; k <= j->spec_end; ++k) {
        short *p = &data[stbi__jpeg_dezigzag[k]];
        if (*p != 0)
          if (stbi__jpeg_get_bit(j))
            if ((*p & bit) == 0) {
              if (*p > 0)
                *p += bit;
              else
                *p -= bit;
            }
      }
    } else {
      k = j->spec_start;
      do {
        rs = stbi__jpeg_huff_decode(j, hac);
        if (rs < 0) return stbi__err("bad huffman code", "Corrupt JPEG");
        s = rs & 15;
        r = rs >> 4;
        if (s == 0) {
          if (r < 15) {
            j->eob_run = (1 << r) - 1;
            if (r) j->eob_run += stbi__jpeg_get_bits(j, r);
            r = 64;  // force end of block
          } else {
            // r=15 s=0 should write 16 0s, so we just do
            // a run of 15 0s and then write s (which is 0),
            // so we don't have to do anything special here
          }
        } else {
          if (s != 1) return stbi__err("bad huffman code", "Corrupt JPEG");
          // sign bit
          if (stbi__jpeg_get_bit(j)) {
            s = bit;
          } else {
            s = -bit;
          }
        }
        // advance by r
        while (k <= j->spec_end) {
          short *p = &data[stbi__jpeg_dezigzag[k++]];
          if (*p != 0) {
            if (stbi__jpeg_get_bit(j))
              if ((*p & bit) == 0) {
                if (*p > 0)
                  *p += bit;
                else
                  *p -= bit;
              }
          } else {
            if (r == 0) {
              *p = (short)s;
              break;
            }
            --r;
          }
        }
      } while (k <= j->spec_end);
    }
  }
  return 1;
}

// take a -128..127 value and stbi__clamp it and convert to 0..255
forceinline unsigned char stbi__clamp(int x) {
  // trick to use a single test to catch both cases
  if ((unsigned int)x > 255) {
    if (x < 0) return 0;
    if (x > 255) return 255;
  }
  return (unsigned char)x;
}

#define STBI__MARKER_none 0xff
// if there's a pending marker from the entropy stream, return that
// otherwise, fetch from the stream and get a marker. if there's no
// marker, return 0xff, which is never a valid marker value
static unsigned char stbi__get_marker(stbi__jpeg *j) {
  unsigned char x;
  if (j->marker != STBI__MARKER_none) {
    x = j->marker;
    j->marker = STBI__MARKER_none;
    return x;
  }
  x = stbi__get8(j->s);
  if (x != 0xff) return STBI__MARKER_none;
  while (x == 0xff) x = stbi__get8(j->s);  // consume repeated 0xff fill bytes
  return x;
}

// in each scan, we'll have scan_n components, and the order
// of the components is specified by order[]
#define STBI__RESTART(x) ((x) >= 0xd0 && (x) <= 0xd7)

// after a restart interval, stbi__jpeg_reset the entropy decoder and
// the dc prediction
static void stbi__jpeg_reset(stbi__jpeg *j) {
  j->code_bits = 0;
  j->code_buffer = 0;
  j->nomore = 0;
  j->img_comp[0].dc_pred = j->img_comp[1].dc_pred = j->img_comp[2].dc_pred =
      j->img_comp[3].dc_pred = 0;
  j->marker = STBI__MARKER_none;
  j->todo = j->restart_interval ? j->restart_interval : 0x7fffffff;
  j->eob_run = 0;
  // no more than 1<<31 MCUs if no restart_interal? that's plenty safe,
  // since we don't even allow 1<<30 pixels
}

static int stbi__parse_entropy_coded_data(stbi__jpeg *z) {
  stbi__jpeg_reset(z);
  if (!z->progressive) {
    if (z->scan_n == 1) {
      int i, j;
      short data[64] forcealign(16);
      int n = z->order[0];
      // non-interleaved data, we just need to process one block at a time,
      // in trivial scanline order
      // number of blocks to do just depends on how many actual "pixels" this
      // component has, independent of interleaved MCU blocking and such
      int w = (z->img_comp[n].x + 7) >> 3;
      int h = (z->img_comp[n].y + 7) >> 3;
      for (j = 0; j < h; ++j) {
        for (i = 0; i < w; ++i) {
          int ha = z->img_comp[n].ha;
          if (!stbi__jpeg_decode_block(z, data, z->huff_dc + z->img_comp[n].hd,
                                       z->huff_ac + ha, z->fast_ac[ha], n,
                                       z->dequant[z->img_comp[n].tq]))
            return 0;
          stbi__idct_simd$sse(
              z->img_comp[n].data + z->img_comp[n].w2 * j * 8 + i * 8,
              z->img_comp[n].w2, data);
          // every data block is an MCU, so countdown the restart interval
          if (--z->todo <= 0) {
            if (z->code_bits < 24) stbi__grow_buffer_unsafe(z);
            // if it's NOT a restart, then just bail, so we get corrupt data
            // rather than no data
            if (!STBI__RESTART(z->marker)) return 1;
            stbi__jpeg_reset(z);
          }
        }
      }
      return 1;
    } else {  // interleaved
      int i, j, k, x, y;
      short data[64] forcealign(16);
      for (j = 0; j < z->img_mcu_y; ++j) {
        for (i = 0; i < z->img_mcu_x; ++i) {
          // scan an interleaved mcu... process scan_n components in order
          for (k = 0; k < z->scan_n; ++k) {
            int n = z->order[k];
            // scan out an mcu's worth of this component; that's just determined
            // by the basic H and V specified for the component
            for (y = 0; y < z->img_comp[n].v; ++y) {
              for (x = 0; x < z->img_comp[n].h; ++x) {
                int x2 = (i * z->img_comp[n].h + x) * 8;
                int y2 = (j * z->img_comp[n].v + y) * 8;
                int ha = z->img_comp[n].ha;
                if (!stbi__jpeg_decode_block(z, data,
                                             z->huff_dc + z->img_comp[n].hd,
                                             z->huff_ac + ha, z->fast_ac[ha], n,
                                             z->dequant[z->img_comp[n].tq]))
                  return 0;
                stbi__idct_simd$sse(
                    z->img_comp[n].data + z->img_comp[n].w2 * y2 + x2,
                    z->img_comp[n].w2, data);
              }
            }
          }
          // after all interleaved components, that's an interleaved MCU,
          // so now count down the restart interval
          if (--z->todo <= 0) {
            if (z->code_bits < 24) stbi__grow_buffer_unsafe(z);
            if (!STBI__RESTART(z->marker)) return 1;
            stbi__jpeg_reset(z);
          }
        }
      }
      return 1;
    }
  } else {
    if (z->scan_n == 1) {
      int i, j;
      int n = z->order[0];
      // non-interleaved data, we just need to process one block at a time,
      // in trivial scanline order
      // number of blocks to do just depends on how many actual "pixels" this
      // component has, independent of interleaved MCU blocking and such
      int w = (z->img_comp[n].x + 7) >> 3;
      int h = (z->img_comp[n].y + 7) >> 3;
      for (j = 0; j < h; ++j) {
        for (i = 0; i < w; ++i) {
          short *data =
              z->img_comp[n].coeff + 64 * (i + j * z->img_comp[n].coeff_w);
          if (z->spec_start == 0) {
            if (!stbi__jpeg_decode_block_prog_dc(
                    z, data, &z->huff_dc[z->img_comp[n].hd], n))
              return 0;
          } else {
            int ha = z->img_comp[n].ha;
            if (!stbi__jpeg_decode_block_prog_ac(z, data, &z->huff_ac[ha],
                                                 z->fast_ac[ha]))
              return 0;
          }
          // every data block is an MCU, so countdown the restart interval
          if (--z->todo <= 0) {
            if (z->code_bits < 24) stbi__grow_buffer_unsafe(z);
            if (!STBI__RESTART(z->marker)) return 1;
            stbi__jpeg_reset(z);
          }
        }
      }
      return 1;
    } else {  // interleaved
      int i, j, k, x, y;
      for (j = 0; j < z->img_mcu_y; ++j) {
        for (i = 0; i < z->img_mcu_x; ++i) {
          // scan an interleaved mcu... process scan_n components in order
          for (k = 0; k < z->scan_n; ++k) {
            int n = z->order[k];
            // scan out an mcu's worth of this component; that's just determined
            // by the basic H and V specified for the component
            for (y = 0; y < z->img_comp[n].v; ++y) {
              for (x = 0; x < z->img_comp[n].h; ++x) {
                int x2 = (i * z->img_comp[n].h + x);
                int y2 = (j * z->img_comp[n].v + y);
                short *data = z->img_comp[n].coeff +
                              64 * (x2 + y2 * z->img_comp[n].coeff_w);
                if (!stbi__jpeg_decode_block_prog_dc(
                        z, data, &z->huff_dc[z->img_comp[n].hd], n))
                  return 0;
              }
            }
          }
          // after all interleaved components, that's an interleaved MCU,
          // so now count down the restart interval
          if (--z->todo <= 0) {
            if (z->code_bits < 24) stbi__grow_buffer_unsafe(z);
            if (!STBI__RESTART(z->marker)) return 1;
            stbi__jpeg_reset(z);
          }
        }
      }
      return 1;
    }
  }
}

static void stbi__jpeg_dequantize(short *data, uint16_t *dequant) {
  int i;
  for (i = 0; i < 64; ++i) data[i] *= dequant[i];
}

static void stbi__jpeg_finish(stbi__jpeg *z) {
  if (z->progressive) {
    // dequantize and idct the data
    int i, j, n;
    for (n = 0; n < z->s->img_n; ++n) {
      int w = (z->img_comp[n].x + 7) >> 3;
      int h = (z->img_comp[n].y + 7) >> 3;
      for (j = 0; j < h; ++j) {
        for (i = 0; i < w; ++i) {
          short *data =
              z->img_comp[n].coeff + 64 * (i + j * z->img_comp[n].coeff_w);
          stbi__jpeg_dequantize(data, z->dequant[z->img_comp[n].tq]);
          stbi__idct_simd$sse(
              z->img_comp[n].data + z->img_comp[n].w2 * j * 8 + i * 8,
              z->img_comp[n].w2, data);
        }
      }
    }
  }
}

static int stbi__process_marker(stbi__jpeg *z, int m) {
  int L;
  switch (m) {
    case STBI__MARKER_none:  // no marker found
      return stbi__err("expected marker", "Corrupt JPEG");

    case 0xDD:  // DRI - specify restart interval
      if (stbi__get16be(z->s) != 4)
        return stbi__err("bad DRI len", "Corrupt JPEG");
      z->restart_interval = stbi__get16be(z->s);
      return 1;

    case 0xDB:  // DQT - define quantization table
      L = stbi__get16be(z->s) - 2;
      while (L > 0) {
        int q = stbi__get8(z->s);
        int p = q >> 4, sixteen = (p != 0);
        int t = q & 15, i;
        if (p != 0 && p != 1) return stbi__err("bad DQT type", "Corrupt JPEG");
        if (t > 3) return stbi__err("bad DQT table", "Corrupt JPEG");

        for (i = 0; i < 64; ++i)
          z->dequant[t][stbi__jpeg_dezigzag[i]] =
              (uint16_t)(sixteen ? stbi__get16be(z->s) : stbi__get8(z->s));
        L -= (sixteen ? 129 : 65);
      }
      return L == 0;

    case 0xC4:  // DHT - define huffman table
      L = stbi__get16be(z->s) - 2;
      while (L > 0) {
        unsigned char *v;
        int sizes[16], i, n = 0;
        int q = stbi__get8(z->s);
        int tc = q >> 4;
        int th = q & 15;
        if (tc > 1 || th > 3)
          return stbi__err("bad DHT header", "Corrupt JPEG");
        for (i = 0; i < 16; ++i) {
          sizes[i] = stbi__get8(z->s);
          n += sizes[i];
        }
        L -= 17;
        if (tc == 0) {
          if (!stbi__build_huffman(z->huff_dc + th, sizes)) return 0;
          v = z->huff_dc[th].values;
        } else {
          if (!stbi__build_huffman(z->huff_ac + th, sizes)) return 0;
          v = z->huff_ac[th].values;
        }
        for (i = 0; i < n; ++i) v[i] = stbi__get8(z->s);
        if (tc != 0) stbi__build_fast_ac(z->fast_ac[th], z->huff_ac + th);
        L -= n;
      }
      return L == 0;
  }

  // check for comment block or APP blocks
  if ((m >= 0xE0 && m <= 0xEF) || m == 0xFE) {
    L = stbi__get16be(z->s);
    if (L < 2) {
      if (m == 0xFE)
        return stbi__err("bad COM len", "Corrupt JPEG");
      else
        return stbi__err("bad APP len", "Corrupt JPEG");
    }
    L -= 2;

    if (m == 0xE0 && L >= 5) {  // JFIF APP0 segment
      static const unsigned char tag[5] = {'J', 'F', 'I', 'F', '\0'};
      int ok = 1;
      int i;
      for (i = 0; i < 5; ++i)
        if (stbi__get8(z->s) != tag[i]) ok = 0;
      L -= 5;
      if (ok) z->jfif = 1;
    } else if (m == 0xEE && L >= 12) {  // Adobe APP14 segment
      static const unsigned char tag[6] = {'A', 'd', 'o', 'b', 'e', '\0'};
      int ok = 1;
      int i;
      for (i = 0; i < 6; ++i)
        if (stbi__get8(z->s) != tag[i]) ok = 0;
      L -= 6;
      if (ok) {
        stbi__get8(z->s);                             // version
        stbi__get16be(z->s);                          // flags0
        stbi__get16be(z->s);                          // flags1
        z->app14_color_transform = stbi__get8(z->s);  // color transform
        L -= 6;
      }
    }

    stbi__skip(z->s, L);
    return 1;
  }

  return stbi__err("unknown marker", "Corrupt JPEG");
}

// after we see SOS
static int stbi__process_scan_header(stbi__jpeg *z) {
  int i;
  int Ls = stbi__get16be(z->s);
  z->scan_n = stbi__get8(z->s);
  if (z->scan_n < 1 || z->scan_n > 4 || z->scan_n > (int)z->s->img_n)
    return stbi__err("bad SOS component count", "Corrupt JPEG");
  if (Ls != 6 + 2 * z->scan_n) return stbi__err("bad SOS len", "Corrupt JPEG");
  for (i = 0; i < z->scan_n; ++i) {
    int id = stbi__get8(z->s), which;
    int q = stbi__get8(z->s);
    for (which = 0; which < z->s->img_n; ++which)
      if (z->img_comp[which].id == id) break;
    if (which == z->s->img_n) return 0;  // no match
    z->img_comp[which].hd = q >> 4;
    if (z->img_comp[which].hd > 3)
      return stbi__err("bad DC huff", "Corrupt JPEG");
    z->img_comp[which].ha = q & 15;
    if (z->img_comp[which].ha > 3)
      return stbi__err("bad AC huff", "Corrupt JPEG");
    z->order[i] = which;
  }

  {
    int aa;
    z->spec_start = stbi__get8(z->s);
    z->spec_end = stbi__get8(z->s);  // should be 63, but might be 0
    aa = stbi__get8(z->s);
    z->succ_high = (aa >> 4);
    z->succ_low = (aa & 15);
    if (z->progressive) {
      if (z->spec_start > 63 || z->spec_end > 63 ||
          z->spec_start > z->spec_end || z->succ_high > 13 || z->succ_low > 13)
        return stbi__err("bad SOS", "Corrupt JPEG");
    } else {
      if (z->spec_start != 0) return stbi__err("bad SOS", "Corrupt JPEG");
      if (z->succ_high != 0 || z->succ_low != 0)
        return stbi__err("bad SOS", "Corrupt JPEG");
      z->spec_end = 63;
    }
  }

  return 1;
}

static int stbi__free_jpeg_components(stbi__jpeg *z, int ncomp, int why) {
  int i;
  for (i = 0; i < ncomp; ++i) {
    if (z->img_comp[i].data) {
      free(z->img_comp[i].data);
      z->img_comp[i].data = NULL;
    }
    if (z->img_comp[i].coeff) {
      free(z->img_comp[i].coeff);
      z->img_comp[i].coeff = NULL;
    }
    if (z->img_comp[i].linebuf) {
      free(z->img_comp[i].linebuf);
      z->img_comp[i].linebuf = NULL;
    }
  }
  return why;
}

static int stbi__process_frame_header(stbi__jpeg *z, int scan) {
  stbi__context *s = z->s;
  int Lf, p, i, q, h_max = 1, v_max = 1, c;
  Lf = stbi__get16be(s);
  if (Lf < 11) return stbi__err("bad SOF len", "Corrupt JPEG");  // JPEG
  p = stbi__get8(s);
  if (p != 8)
    return stbi__err("only 8-bit",
                     "JPEG format not supported: 8-bit only");  // JPEG baseline
  s->img_y = stbi__get16be(s);
  if (s->img_y == 0)
    return stbi__err(
        "no header height",
        "JPEG format not supported: delayed height");  // Legal, but we don't
  // handle it--but neither
  // does IJG
  s->img_x = stbi__get16be(s);
  if (s->img_x == 0)
    return stbi__err("0 width", "Corrupt JPEG");  // JPEG requires
  c = stbi__get8(s);
  if (c != 3 && c != 1 && c != 4)
    return stbi__err("bad component count", "Corrupt JPEG");
  s->img_n = c;
  for (i = 0; i < c; ++i) {
    z->img_comp[i].data = NULL;
    z->img_comp[i].linebuf = NULL;
  }

  if (Lf != 8 + 3 * s->img_n) return stbi__err("bad SOF len", "Corrupt JPEG");

  z->rgb = 0;
  for (i = 0; i < s->img_n; ++i) {
    static const unsigned char rgb[3] = {'R', 'G', 'B'};
    z->img_comp[i].id = stbi__get8(s);
    if (s->img_n == 3 && z->img_comp[i].id == rgb[i]) ++z->rgb;
    q = stbi__get8(s);
    z->img_comp[i].h = (q >> 4);
    if (!z->img_comp[i].h || z->img_comp[i].h > 4)
      return stbi__err("bad H", "Corrupt JPEG");
    z->img_comp[i].v = q & 15;
    if (!z->img_comp[i].v || z->img_comp[i].v > 4)
      return stbi__err("bad V", "Corrupt JPEG");
    z->img_comp[i].tq = stbi__get8(s);
    if (z->img_comp[i].tq > 3) return stbi__err("bad TQ", "Corrupt JPEG");
  }

  if (scan != STBI__SCAN_load) return 1;

  if (!stbi__mad3sizes_valid(s->img_x, s->img_y, s->img_n, 0))
    return stbi__err("too large", "Image too large to decode");

  for (i = 0; i < s->img_n; ++i) {
    if (z->img_comp[i].h > h_max) h_max = z->img_comp[i].h;
    if (z->img_comp[i].v > v_max) v_max = z->img_comp[i].v;
  }

  // compute interleaved mcu info
  z->img_h_max = h_max;
  z->img_v_max = v_max;
  z->img_mcu_w = h_max * 8;
  z->img_mcu_h = v_max * 8;
  // these sizes can't be more than 17 bits
  z->img_mcu_x = (s->img_x + z->img_mcu_w - 1) / z->img_mcu_w;
  z->img_mcu_y = (s->img_y + z->img_mcu_h - 1) / z->img_mcu_h;

  for (i = 0; i < s->img_n; ++i) {
    // number of effective pixels (e.g. for non-interleaved MCU)
    z->img_comp[i].x = (s->img_x * z->img_comp[i].h + h_max - 1) / h_max;
    z->img_comp[i].y = (s->img_y * z->img_comp[i].v + v_max - 1) / v_max;
    // to simplify generation, we'll allocate enough memory to decode
    // the bogus oversized data from using interleaved MCUs and their
    // big blocks (e.g. a 16x16 iMCU on an image of width 33); we won't
    // discard the extra data until colorspace conversion
    //
    // img_mcu_x, img_mcu_y: <=17 bits; comp[i].h and .v are <=4 (checked
    // earlier) so these muls can't overflow with 32-bit ints (which we require)
    z->img_comp[i].w2 = z->img_mcu_x * z->img_comp[i].h * 8;
    z->img_comp[i].h2 = z->img_mcu_y * z->img_comp[i].v * 8;
    z->img_comp[i].coeff = NULL;
    z->img_comp[i].linebuf = NULL;
    z->img_comp[i].data =
        stbi__malloc_mad2(z->img_comp[i].w2, z->img_comp[i].h2, 15);
    if (z->progressive) {
      // w2, h2 are multiples of 8 (see above)
      z->img_comp[i].coeff_w = z->img_comp[i].w2 / 8;
      z->img_comp[i].coeff_h = z->img_comp[i].h2 / 8;
      z->img_comp[i].coeff = stbi__malloc_mad3(
          z->img_comp[i].w2, z->img_comp[i].h2, sizeof(short), 15);
    }
  }

  return 1;
}

// use comparisons since in some cases we handle more than one case (e.g. SOF)
#define stbi__DNL(x) ((x) == 0xdc)
#define stbi__SOI(x) ((x) == 0xd8)
#define stbi__EOI(x) ((x) == 0xd9)
#define stbi__SOF(x) ((x) == 0xc0 || (x) == 0xc1 || (x) == 0xc2)
#define stbi__SOS(x) ((x) == 0xda)

#define stbi__SOF_progressive(x) ((x) == 0xc2)

static int stbi__decode_jpeg_header(stbi__jpeg *z, int scan) {
  int m;
  z->jfif = 0;
  z->app14_color_transform = -1;  // valid values are 0,1,2
  z->marker = STBI__MARKER_none;  // initialize cached marker to empty
  m = stbi__get_marker(z);
  if (!stbi__SOI(m)) return 0;
  if (scan == STBI__SCAN_type) return 1;
  m = stbi__get_marker(z);
  while (!stbi__SOF(m)) {
    if (!stbi__process_marker(z, m)) return 0;
    m = stbi__get_marker(z);
    while (m == STBI__MARKER_none) {
      // some files have extra padding after their blocks, so ok, we'll scan
      if (stbi__at_eof(z->s)) return stbi__err("no SOF", "Corrupt JPEG");
      m = stbi__get_marker(z);
    }
  }
  z->progressive = stbi__SOF_progressive(m);
  if (!stbi__process_frame_header(z, scan)) return 0;
  return 1;
}

// decode image to YCbCr format
static int stbi__decode_jpeg_image(stbi__jpeg *j) {
  int m;
  for (m = 0; m < 4; m++) {
    j->img_comp[m].data = NULL;
    j->img_comp[m].coeff = NULL;
  }
  j->restart_interval = 0;
  if (!stbi__decode_jpeg_header(j, STBI__SCAN_load)) return 0;
  m = stbi__get_marker(j);
  while (!stbi__EOI(m)) {
    if (stbi__SOS(m)) {
      if (!stbi__process_scan_header(j)) return 0;
      if (!stbi__parse_entropy_coded_data(j)) return 0;
      if (j->marker == STBI__MARKER_none) {
        // handle 0s at the end of image data from IP Kamera 9060
        while (!stbi__at_eof(j->s)) {
          int x = stbi__get8(j->s);
          if (x == 255) {
            j->marker = stbi__get8(j->s);
            break;
          }
        }
        // if we reach eof without hitting a marker, stbi__get_marker() below
        // will fail and we'll eventually return 0
      }
    } else if (stbi__DNL(m)) {
      int Ld = stbi__get16be(j->s);
      uint32_t NL = stbi__get16be(j->s);
      if (Ld != 4) return stbi__err("bad DNL len", "Corrupt JPEG");
      if (NL != j->s->img_y) return stbi__err("bad DNL height", "Corrupt JPEG");
    } else {
      if (!stbi__process_marker(j, m)) return 0;
    }
    m = stbi__get_marker(j);
  }
  if (j->progressive) stbi__jpeg_finish(j);
  return 1;
}

// static jfif-centered resampling (across block boundaries)

typedef unsigned char *(*resample_row_func)(unsigned char *out,
                                            unsigned char *in0,
                                            unsigned char *in1, int w, int hs);

#define stbi__div4(x) ((unsigned char)((x) >> 2))

static unsigned char *resample_row_1(unsigned char *out, unsigned char *in_near,
                                     unsigned char *in_far, int w, int hs) {
  return in_near;
}

static unsigned char *stbi__resample_row_v_2(unsigned char *out,
                                             unsigned char *in_near,
                                             unsigned char *in_far, int w,
                                             int hs) {
  // need to generate two samples vertically for every one in input
  int i;
  for (i = 0; i < w; ++i) out[i] = stbi__div4(3 * in_near[i] + in_far[i] + 2);
  return out;
}

static unsigned char *stbi__resample_row_h_2(unsigned char *out,
                                             unsigned char *in_near,
                                             unsigned char *in_far, int w,
                                             int hs) {
  // need to generate two samples horizontally for every one in input
  int i;
  unsigned char *input = in_near;
  if (w == 1) {
    // if only one sample, can't do any interpolation
    out[0] = out[1] = input[0];
    return out;
  }
  out[0] = input[0];
  out[1] = stbi__div4(input[0] * 3 + input[1] + 2);
  for (i = 1; i < w - 1; ++i) {
    int n = 3 * input[i] + 2;
    out[i * 2 + 0] = stbi__div4(n + input[i - 1]);
    out[i * 2 + 1] = stbi__div4(n + input[i + 1]);
  }
  out[i * 2 + 0] = stbi__div4(input[w - 2] * 3 + input[w - 1] + 2);
  out[i * 2 + 1] = input[w - 1];
  return out;
}

#define stbi__div16(x) ((unsigned char)((x) >> 4))

static unsigned char *stbi__resample_row_hv_2(unsigned char *out,
                                              unsigned char *in_near,
                                              unsigned char *in_far, int w,
                                              int hs) {
  // need to generate 2x2 samples for every one in input
  int i, t0, t1;
  if (w == 1) {
    out[0] = out[1] = stbi__div4(3 * in_near[0] + in_far[0] + 2);
    return out;
  }
  t1 = 3 * in_near[0] + in_far[0];
  out[0] = stbi__div4(t1 + 2);
  for (i = 1; i < w; ++i) {
    t0 = t1;
    t1 = 3 * in_near[i] + in_far[i];
    out[i * 2 - 1] = stbi__div16(3 * t0 + t1 + 8);
    out[i * 2] = stbi__div16(3 * t1 + t0 + 8);
  }
  out[w * 2 - 1] = stbi__div4(t1 + 2);
  return out;
}

#if defined(STBI_SSE2)
static unsigned char *stbi__resample_row_hv_2_simd(unsigned char *out,
                                                   unsigned char *in_near,
                                                   unsigned char *in_far, int w,
                                                   int hs) {
  // need to generate 2x2 samples for every one in input
  int i = 0, t0, t1;
  if (w == 1) {
    out[0] = out[1] = stbi__div4(3 * in_near[0] + in_far[0] + 2);
    return out;
  }
  t1 = 3 * in_near[0] + in_far[0];
  // process groups of 8 pixels for as long as we can.
  // note we can't handle the last pixel in a row in this loop
  // because we need to handle the filter boundary conditions.
  for (; i < ((w - 1) & ~7); i += 8) {
    // load and perform the vertical filtering pass
    // this uses 3*x + y = 4*x + (y - x)
    __m128i zero = _mm_setzero_si128();
    __m128i farb = _mm_loadl_epi64((__m128i *)(in_far + i));
    __m128i nearb = _mm_loadl_epi64((__m128i *)(in_near + i));
    __m128i farw = _mm_unpacklo_epi8(farb, zero);
    __m128i nearw = _mm_unpacklo_epi8(nearb, zero);
    __m128i diff = _mm_sub_epi16(farw, nearw);
    __m128i nears = _mm_slli_epi16(nearw, 2);
    __m128i curr = _mm_add_epi16(nears, diff);  // current row
    // horizontal filter works the same based on shifted vers of current
    // row. "prev" is current row shifted right by 1 pixel; we need to
    // insert the previous pixel value (from t1).
    // "next" is current row shifted left by 1 pixel, with first pixel
    // of next block of 8 pixels added in.
    __m128i prv0 = _mm_slli_si128(curr, 2);
    __m128i nxt0 = _mm_srli_si128(curr, 2);
    __m128i prev = _mm_insert_epi16(prv0, t1, 0);
    __m128i next =
        _mm_insert_epi16(nxt0, 3 * in_near[i + 8] + in_far[i + 8], 7);
    // horizontal filter, polyphase implementation since it's convenient:
    // even pixels = 3*cur + prev = cur*4 + (prev - cur)
    // odd  pixels = 3*cur + next = cur*4 + (next - cur)
    // note the shared term.
    __m128i bias = _mm_set1_epi16(8);
    __m128i curs = _mm_slli_epi16(curr, 2);
    __m128i prvd = _mm_sub_epi16(prev, curr);
    __m128i nxtd = _mm_sub_epi16(next, curr);
    __m128i curb = _mm_add_epi16(curs, bias);
    __m128i even = _mm_add_epi16(prvd, curb);
    __m128i odd = _mm_add_epi16(nxtd, curb);
    // interleave even and odd pixels, then undo scaling.
    __m128i int0 = _mm_unpacklo_epi16(even, odd);
    __m128i int1 = _mm_unpackhi_epi16(even, odd);
    __m128i de0 = _mm_srli_epi16(int0, 4);
    __m128i de1 = _mm_srli_epi16(int1, 4);
    // pack and write output
    __m128i outv = _mm_packus_epi16(de0, de1);
    _mm_storeu_si128((__m128i *)(out + i * 2), outv);
    // "previous" value for next iter
    t1 = 3 * in_near[i + 7] + in_far[i + 7];
  }
  t0 = t1;
  t1 = 3 * in_near[i] + in_far[i];
  out[i * 2] = stbi__div16(3 * t1 + t0 + 8);
  for (++i; i < w; ++i) {
    t0 = t1;
    t1 = 3 * in_near[i] + in_far[i];
    out[i * 2 - 1] = stbi__div16(3 * t0 + t1 + 8);
    out[i * 2] = stbi__div16(3 * t1 + t0 + 8);
  }
  out[w * 2 - 1] = stbi__div4(t1 + 2);
  return out;
}
#endif

static unsigned char *stbi__resample_row_nearest(unsigned char *out,
                                                 unsigned char *in_near,
                                                 unsigned char *in_far, int w,
                                                 int hs) {
  int i, j;
  for (i = 0; i < w; ++i) {
    for (j = 0; j < hs; ++j) {
      out[i * hs + j] = in_near[i];
    }
  }
  return out;
}

// set up the kernels
static void stbi__setup_jpeg(stbi__jpeg *j) {
  j->resample_row_hv_2_kernel = stbi__resample_row_hv_2;
#if 0
  if (stbi__sse2_available()) {
    j->resample_row_hv_2_kernel = stbi__resample_row_hv_2_simd;
  }
#endif
}

// clean up the temporary component buffers
static void stbi__cleanup_jpeg(stbi__jpeg *j) {
  stbi__free_jpeg_components(j, j->s->img_n, 0);
}

typedef struct {
  resample_row_func resample;
  unsigned char *line0, *line1;
  int hs, vs;   // expansion factor in each axis
  int w_lores;  // horizontal pixels pre-expansion
  int ystep;    // how far through vertical expansion we are
  int ypos;     // which pre-expansion row we're on
} stbi__resample;

// fast 0..255 * 0..255 => 0..255 rounded multiplication
static unsigned char stbi__blinn_8x8(unsigned char x, unsigned char y) {
  unsigned t;
  t = x * y + 128;
  return (t + (t >> 8)) >> 8;
}

static unsigned char *load_jpeg_image(stbi__jpeg *z, int *out_x, int *out_y,
                                      int *comp, int req_comp) {
  int n, decode_n, is_rgb;
  z->s->img_n = 0;  // make stbi__cleanup_jpeg safe

  // validate req_comp
  if (req_comp < 0 || req_comp > 4) {
    return stbi__errpuc("bad req_comp", "Internal error");
  }

  // load a jpeg image from whichever source, but leave in YCbCr format
  if (!stbi__decode_jpeg_image(z)) {
    stbi__cleanup_jpeg(z);
    return NULL;
  }

  // determine actual number of components to generate
  n = req_comp ? req_comp : z->s->img_n >= 3 ? 3 : 1;
  is_rgb = z->s->img_n == 3 &&
           (z->rgb == 3 || (z->app14_color_transform == 0 && !z->jfif));
  if (z->s->img_n == 3 && n < 3 && !is_rgb) {
    decode_n = 1;
  } else {
    decode_n = z->s->img_n;
  }

  // resample and color-convert
  {
    int k;
    unsigned int i, j;
    unsigned char *output;
    unsigned char *coutput[4];
    stbi__resample res_comp[4];
    bzero(coutput, sizeof(coutput));

    for (k = 0; k < decode_n; ++k) {
      stbi__resample *r = &res_comp[k];

      // allocate line buffer big enough for upsampling off the edges
      // with upsample factor of 4
      z->img_comp[k].linebuf = xmalloc(z->s->img_x + 3);

      r->hs = z->img_h_max / z->img_comp[k].h;
      r->vs = z->img_v_max / z->img_comp[k].v;
      r->ystep = r->vs >> 1;
      r->w_lores = (z->s->img_x + r->hs - 1) / r->hs;
      r->ypos = 0;
      r->line0 = r->line1 = z->img_comp[k].data;

      if (r->hs == 1 && r->vs == 1) {
        r->resample = resample_row_1;
      } else if (r->hs == 1 && r->vs == 2) {
        r->resample = stbi__resample_row_v_2;
      } else if (r->hs == 2 && r->vs == 1) {
        r->resample = stbi__resample_row_h_2;
      } else if (r->hs == 2 && r->vs == 2) {
        r->resample = z->resample_row_hv_2_kernel;
      } else {
        r->resample = stbi__resample_row_nearest;
      }
    }

    // can't error after this so, this is safe
    output = stbi__malloc_mad3(n, z->s->img_x, z->s->img_y, 1);

    // now go ahead and resample
    for (j = 0; j < z->s->img_y; ++j) {
      unsigned char *out = output + n * z->s->img_x * j;
      for (k = 0; k < decode_n; ++k) {
        stbi__resample *r = &res_comp[k];
        int y_bot = r->ystep >= (r->vs >> 1);
        coutput[k] =
            r->resample(z->img_comp[k].linebuf, y_bot ? r->line1 : r->line0,
                        y_bot ? r->line0 : r->line1, r->w_lores, r->hs);
        if (++r->ystep >= r->vs) {
          r->ystep = 0;
          r->line0 = r->line1;
          if (++r->ypos < z->img_comp[k].y) r->line1 += z->img_comp[k].w2;
        }
      }
      if (n >= 3) {
        unsigned char *y = coutput[0];
        if (z->s->img_n == 3) {
          if (is_rgb) {
            for (i = 0; i < z->s->img_x; ++i) {
              out[0] = y[i];
              out[1] = coutput[1][i];
              out[2] = coutput[2][i];
              out[3] = 255;
              out += n;
            }
          } else {
            stbi__YCbCr_to_RGB_row(out, y, coutput[1], coutput[2], z->s->img_x,
                                   n);
          }
        } else if (z->s->img_n == 4) {
          if (z->app14_color_transform == 0) {  // CMYK
            for (i = 0; i < z->s->img_x; ++i) {
              unsigned char m = coutput[3][i];
              out[0] = stbi__blinn_8x8(coutput[0][i], m);
              out[1] = stbi__blinn_8x8(coutput[1][i], m);
              out[2] = stbi__blinn_8x8(coutput[2][i], m);
              out[3] = 255;
              out += n;
            }
          } else if (z->app14_color_transform == 2) {  // YCCK
            stbi__YCbCr_to_RGB_row(out, y, coutput[1], coutput[2], z->s->img_x,
                                   n);
            for (i = 0; i < z->s->img_x; ++i) {
              unsigned char m = coutput[3][i];
              out[0] = stbi__blinn_8x8(255 - out[0], m);
              out[1] = stbi__blinn_8x8(255 - out[1], m);
              out[2] = stbi__blinn_8x8(255 - out[2], m);
              out += n;
            }
          } else {  // YCbCr + alpha?  Ignore the fourth channel for now
            stbi__YCbCr_to_RGB_row(out, y, coutput[1], coutput[2], z->s->img_x,
                                   n);
          }
        } else
          for (i = 0; i < z->s->img_x; ++i) {
            out[0] = out[1] = out[2] = y[i];
            out[3] = 255;  // not used if n==3
            out += n;
          }
      } else {
        if (is_rgb) {
          if (n == 1)
            for (i = 0; i < z->s->img_x; ++i)
              *out++ =
                  stbi__compute_y(coutput[0][i], coutput[1][i], coutput[2][i]);
          else {
            for (i = 0; i < z->s->img_x; ++i, out += 2) {
              out[0] =
                  stbi__compute_y(coutput[0][i], coutput[1][i], coutput[2][i]);
              out[1] = 255;
            }
          }
        } else if (z->s->img_n == 4 && z->app14_color_transform == 0) {
          for (i = 0; i < z->s->img_x; ++i) {
            unsigned char m = coutput[3][i];
            unsigned char r = stbi__blinn_8x8(coutput[0][i], m);
            unsigned char g = stbi__blinn_8x8(coutput[1][i], m);
            unsigned char b = stbi__blinn_8x8(coutput[2][i], m);
            out[0] = stbi__compute_y(r, g, b);
            out[1] = 255;
            out += n;
          }
        } else if (z->s->img_n == 4 && z->app14_color_transform == 2) {
          for (i = 0; i < z->s->img_x; ++i) {
            out[0] = stbi__blinn_8x8(255 - coutput[0][i], coutput[3][i]);
            out[1] = 255;
            out += n;
          }
        } else {
          unsigned char *y = coutput[0];
          if (n == 1)
            for (i = 0; i < z->s->img_x; ++i) out[i] = y[i];
          else
            for (i = 0; i < z->s->img_x; ++i) {
              *out++ = y[i];
              *out++ = 255;
            }
        }
      }
    }
    stbi__cleanup_jpeg(z);
    *out_x = z->s->img_x;
    *out_y = z->s->img_y;
    if (comp)
      *comp =
          z->s->img_n >= 3 ? 3 : 1;  // report original components, not output
    return output;
  }
}

static noinline void *stbi__jpeg_load(stbi__context *s, int *x, int *y,
                                      int *comp, int req_comp,
                                      stbi__result_info *ri) {
  unsigned char *result;
  stbi__jpeg *j = (stbi__jpeg *)malloc(sizeof(stbi__jpeg));
  j->s = s;
  stbi__setup_jpeg(j);
  result = load_jpeg_image(j, x, y, comp, req_comp);
  free(j);
  return result;
}

static int stbi__jpeg_test(stbi__context *s) {
  int r;
  stbi__jpeg *j;
  j = malloc(sizeof(stbi__jpeg));
  j->s = s;
  stbi__setup_jpeg(j);
  r = stbi__decode_jpeg_header(j, STBI__SCAN_type);
  stbi__rewind(s);
  free(j);
  return r;
}

static int stbi__jpeg_info_raw(stbi__jpeg *j, int *x, int *y, int *comp) {
  if (!stbi__decode_jpeg_header(j, STBI__SCAN_header)) {
    stbi__rewind(j->s);
    return 0;
  }
  if (x) *x = j->s->img_x;
  if (y) *y = j->s->img_y;
  if (comp) *comp = j->s->img_n >= 3 ? 3 : 1;
  return 1;
}

static int stbi__jpeg_info(stbi__context *s, int *x, int *y, int *comp) {
  int result;
  stbi__jpeg *j = (stbi__jpeg *)(malloc(sizeof(stbi__jpeg)));
  j->s = s;
  result = stbi__jpeg_info_raw(j, x, y, comp);
  free(j);
  return result;
}

// public domain zlib decode    v0.2  Sean Barrett 2006-11-18
//    simple implementation
//      - all input must be provided in an upfront buffer
//      - all output is written to a single output buffer (can malloc/realloc)
//    performance
//      - fast huffman

// fast-way is faster to check than jpeg huffman, but slow way is slower
#define STBI__ZFAST_BITS 9  // accelerate all cases in default tables
#define STBI__ZFAST_MASK ((1 << STBI__ZFAST_BITS) - 1)

// zlib-style huffman encoding
// (jpegs packs from left, zlib from right, so can't share code)
typedef struct {
  uint16_t fast[1 << STBI__ZFAST_BITS];
  uint16_t firstcode[16];
  int maxcode[17];
  uint16_t firstsymbol[16];
  unsigned char size[288];
  uint16_t value[288];
} stbi__zhuffman;

forceinline int stbi__bitreverse16(int n) {
  n = ((n & 0xAAAA) >> 1) | ((n & 0x5555) << 1);
  n = ((n & 0xCCCC) >> 2) | ((n & 0x3333) << 2);
  n = ((n & 0xF0F0) >> 4) | ((n & 0x0F0F) << 4);
  n = ((n & 0xFF00) >> 8) | ((n & 0x00FF) << 8);
  return n;
}

forceinline int stbi__bit_reverse(int v, int bits) {
  assert(bits <= 16);
  // to bit reverse n bits, reverse 16 and shift
  // e.g. 11 bits, bit reverse and shift away 5
  return stbi__bitreverse16(v) >> (16 - bits);
}

static int stbi__zbuild_huffman(stbi__zhuffman *z,
                                const unsigned char *sizelist, int num) {
  int i, k = 0;
  int code, next_code[16], sizes[17];
  // DEFLATE spec for generating codes
  bzero(sizes, sizeof(sizes));
  bzero(z->fast, sizeof(z->fast));
  for (i = 0; i < num; ++i) ++sizes[sizelist[i]];
  sizes[0] = 0;
  for (i = 1; i < 16; ++i)
    if (sizes[i] > (1 << i)) return stbi__err("bad sizes", "Corrupt PNG");
  code = 0;
  for (i = 1; i < 16; ++i) {
    next_code[i] = code;
    z->firstcode[i] = (uint16_t)code;
    z->firstsymbol[i] = (uint16_t)k;
    code = (code + sizes[i]);
    if (sizes[i])
      if (code - 1 >= (1 << i))
        return stbi__err("bad codelengths", "Corrupt PNG");
    z->maxcode[i] = code << (16 - i);  // preshift for inner loop
    code <<= 1;
    k += sizes[i];
  }
  z->maxcode[16] = 0x10000;  // sentinel
  for (i = 0; i < num; ++i) {
    int s = sizelist[i];
    if (s) {
      int c = next_code[s] - z->firstcode[s] + z->firstsymbol[s];
      uint16_t fastv = (uint16_t)((s << 9) | i);
      z->size[c] = (unsigned char)s;
      z->value[c] = (uint16_t)i;
      if (s <= STBI__ZFAST_BITS) {
        int j = stbi__bit_reverse(next_code[s], s);
        while (j < (1 << STBI__ZFAST_BITS)) {
          z->fast[j] = fastv;
          j += (1 << s);
        }
      }
      ++next_code[s];
    }
  }
  return 1;
}

// zlib-from-memory implementation for PNG reading
//    because PNG allows splitting the zlib stream arbitrarily,
//    and it's annoying structurally to have PNG call ZLIB call PNG,
//    we require PNG read all the IDATs and combine them into a single
//    memory buffer
typedef struct {
  unsigned char *zbuffer, *zbuffer_end;
  int num_bits;
  uint32_t code_buffer;
  char *zout;
  char *zout_start;
  char *zout_end;
  int z_expandable;
  stbi__zhuffman z_length, z_distance;
} stbi__zbuf;

forceinline unsigned char stbi__zget8(stbi__zbuf *z) {
  if (z->zbuffer >= z->zbuffer_end) return 0;
  return *z->zbuffer++;
}

static void stbi__fill_bits(stbi__zbuf *z) {
  do {
    assert(z->code_buffer < (1u << z->num_bits));
    z->code_buffer |= (unsigned int)stbi__zget8(z) << z->num_bits;
    z->num_bits += 8;
  } while (z->num_bits <= 24);
}

forceinline unsigned int stbi__zreceive(stbi__zbuf *z, int n) {
  unsigned int k;
  if (z->num_bits < n) stbi__fill_bits(z);
  k = z->code_buffer & ((1 << n) - 1);
  z->code_buffer >>= n;
  z->num_bits -= n;
  return k;
}

static int stbi__zhuffman_decode_slowpath(stbi__zbuf *a, stbi__zhuffman *z) {
  int b, s, k;
  // not resolved by fast table, so compute it the slow way
  // use jpeg approach, which requires MSbits at top
  k = stbi__bit_reverse(a->code_buffer, 16);
  for (s = STBI__ZFAST_BITS + 1;; ++s)
    if (k < z->maxcode[s]) break;
  if (s == 16) return -1;  // invalid code!
  // code size is s, so:
  b = (k >> (16 - s)) - z->firstcode[s] + z->firstsymbol[s];
  assert(z->size[b] == s);
  a->code_buffer >>= s;
  a->num_bits -= s;
  return z->value[b];
}

forceinline int stbi__zhuffman_decode(stbi__zbuf *a, stbi__zhuffman *z) {
  int b, s;
  if (a->num_bits < 16) stbi__fill_bits(a);
  b = z->fast[a->code_buffer & STBI__ZFAST_MASK];
  if (b) {
    s = b >> 9;
    a->code_buffer >>= s;
    a->num_bits -= s;
    return b & 511;
  }
  return stbi__zhuffman_decode_slowpath(a, z);
}

static int stbi__zexpand(stbi__zbuf *z, char *zout, int n) {
  char *q;
  int cur, limit, old_limit;
  z->zout = zout;
  if (!z->z_expandable) return stbi__err("output buffer limit", "Corrupt PNG");
  cur = (int)(z->zout - z->zout_start);
  limit = old_limit = (int)(z->zout_end - z->zout_start);
  while (cur + n > limit) limit *= 2;
  q = (char *)STBI_REALLOC_SIZED(z->zout_start, old_limit, limit);
  if (q == NULL) return stbi__err("outofmem", "Out of memory");
  z->zout_start = q;
  z->zout = q + cur;
  z->zout_end = q + limit;
  return 1;
}

static const int stbi__zlength_base[31] = {
    3,  4,  5,  6,  7,  8,  9,  10,  11,  13,  15,  17,  19,  23, 27, 31,
    35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0,  0,
};

static const int stbi__zlength_extra[31] = {
    0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
    3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0, 0, 0,
};

static const int stbi__zdist_base[32] = {
    1,    2,    3,    4,    5,    7,     9,     13,    17,  25,   33,
    49,   65,   97,   129,  193,  257,   385,   513,   769, 1025, 1537,
    2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577, 0,   0,
};

static const int stbi__zdist_extra[32] = {
    0, 0, 0, 0, 1, 1, 2, 2,  3,  3,  4,  4,  5,  5,  6,
    6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13,
};

static int stbi__parse_huffman_block(stbi__zbuf *a) {
  char *zout = a->zout;
  for (;;) {
    int z = stbi__zhuffman_decode(a, &a->z_length);
    if (z < 256) {
      if (z < 0) return stbi__err("bad huffman code", "Corrupt PNG");
      if (zout >= a->zout_end) {
        if (!stbi__zexpand(a, zout, 1)) return 0;
        zout = a->zout;
      }
      *zout++ = (char)z;
    } else {
      unsigned char *p;
      int len, dist;
      if (z == 256) {
        a->zout = zout;
        return 1;
      }
      z -= 257;
      len = stbi__zlength_base[z];
      if (stbi__zlength_extra[z])
        len += stbi__zreceive(a, stbi__zlength_extra[z]);
      z = stbi__zhuffman_decode(a, &a->z_distance);
      if (z < 0) return stbi__err("bad huffman code", "Corrupt PNG");
      dist = stbi__zdist_base[z];
      if (stbi__zdist_extra[z]) dist += stbi__zreceive(a, stbi__zdist_extra[z]);
      if (zout - a->zout_start < dist)
        return stbi__err("bad dist", "Corrupt PNG");
      if (zout + len > a->zout_end) {
        if (!stbi__zexpand(a, zout, len)) return 0;
        zout = a->zout;
      }
      p = (unsigned char *)(zout - dist);
      if (dist == 1) {  // run of one byte; common in images.
        unsigned char v = *p;
        if (len) {
          do *zout++ = v;
          while (--len);
        }
      } else {
        if (len) {
          do *zout++ = *p++;
          while (--len);
        }
      }
    }
  }
}

static int stbi__compute_huffman_codes(stbi__zbuf *a) {
  static const unsigned char length_dezigzag[19] = {
      16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
  stbi__zhuffman z_codelength;
  unsigned char lencodes[286 + 32 + 137];  // padding for maximum single op
  unsigned char codelength_sizes[19];
  int i, n;
  int hlit = stbi__zreceive(a, 5) + 257;
  int hdist = stbi__zreceive(a, 5) + 1;
  int hclen = stbi__zreceive(a, 4) + 4;
  int ntot = hlit + hdist;
  bzero(codelength_sizes, sizeof(codelength_sizes));
  for (i = 0; i < hclen; ++i) {
    int s = stbi__zreceive(a, 3);
    codelength_sizes[length_dezigzag[i]] = (unsigned char)s;
  }
  if (!stbi__zbuild_huffman(&z_codelength, codelength_sizes, 19)) return 0;
  n = 0;
  while (n < ntot) {
    int c = stbi__zhuffman_decode(a, &z_codelength);
    if (c < 0 || c >= 19) return stbi__err("bad codelengths", "Corrupt PNG");
    if (c < 16)
      lencodes[n++] = (unsigned char)c;
    else {
      unsigned char fill = 0;
      if (c == 16) {
        c = stbi__zreceive(a, 2) + 3;
        if (n == 0) return stbi__err("bad codelengths", "Corrupt PNG");
        fill = lencodes[n - 1];
      } else if (c == 17)
        c = stbi__zreceive(a, 3) + 3;
      else {
        assert(c == 18);
        c = stbi__zreceive(a, 7) + 11;
      }
      if (ntot - n < c) return stbi__err("bad codelengths", "Corrupt PNG");
      memset(lencodes + n, fill, c);
      n += c;
    }
  }
  if (n != ntot) return stbi__err("bad codelengths", "Corrupt PNG");
  if (!stbi__zbuild_huffman(&a->z_length, lencodes, hlit)) return 0;
  if (!stbi__zbuild_huffman(&a->z_distance, lencodes + hlit, hdist)) return 0;
  return 1;
}

static int stbi__parse_uncompressed_block(stbi__zbuf *a) {
  unsigned char header[4];
  int len, nlen, k;
  if (a->num_bits & 7) stbi__zreceive(a, a->num_bits & 7);  // discard
  // drain the bit-packed data into header
  k = 0;
  while (a->num_bits > 0) {
    header[k++] =
        (unsigned char)(a->code_buffer & 255);  // suppress MSVC run-time check
    a->code_buffer >>= 8;
    a->num_bits -= 8;
  }
  assert(a->num_bits == 0);
  // now fill header the normal way
  while (k < 4) header[k++] = stbi__zget8(a);
  len = header[1] * 256 + header[0];
  nlen = header[3] * 256 + header[2];
  if (nlen != (len ^ 0xffff)) return stbi__err("zlib corrupt", "Corrupt PNG");
  if (a->zbuffer + len > a->zbuffer_end)
    return stbi__err("read past buffer", "Corrupt PNG");
  if (a->zout + len > a->zout_end)
    if (!stbi__zexpand(a, a->zout, len)) return 0;
  memcpy(a->zout, a->zbuffer, len);
  a->zbuffer += len;
  a->zout += len;
  return 1;
}

static int stbi__parse_zlib_header(stbi__zbuf *a) {
  int cmf = stbi__zget8(a);
  int cm = cmf & 15;
  /* int cinfo = cmf >> 4; */
  int flg = stbi__zget8(a);
  if ((cmf * 256 + flg) % 31 != 0)
    return stbi__err("bad zlib header", "Corrupt PNG");  // zlib spec
  if (flg & 32)
    return stbi__err("no preset dict",
                     "Corrupt PNG");  // preset dictionary not allowed in png
  if (cm != 8)
    return stbi__err("bad compression",
                     "Corrupt PNG");  // DEFLATE required for png
  // window = 1 << (8 + cinfo)... but who cares, we fully buffer output
  return 1;
}

static const unsigned char stbi__zdefault_length[288] = {
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
    9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
    9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
    9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
    9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
    9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8};

static const unsigned char stbi__zdefault_distance[32] = {
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
};

/*
  Init algorithm:{
  int i;   // use <= to match clearly with spec
  for (i=0; i <= 143; ++i)     stbi__zdefault_length[i]   = 8;
  for (   ; i <= 255; ++i)     stbi__zdefault_length[i]   = 9;
  for (   ; i <= 279; ++i)     stbi__zdefault_length[i]   = 7;
  for (   ; i <= 287; ++i)     stbi__zdefault_length[i]   = 8;
  for (i=0; i <=  31; ++i)     stbi__zdefault_distance[i] = 5;
  }
*/

static int stbi__parse_zlib(stbi__zbuf *a, int parse_header) {
  int final, type;
  if (parse_header)
    if (!stbi__parse_zlib_header(a)) return 0;
  a->num_bits = 0;
  a->code_buffer = 0;
  do {
    final = stbi__zreceive(a, 1);
    type = stbi__zreceive(a, 2);
    if (type == 0) {
      if (!stbi__parse_uncompressed_block(a)) return 0;
    } else if (type == 3) {
      return 0;
    } else {
      if (type == 1) {
        // use fixed code lengths
        if (!stbi__zbuild_huffman(&a->z_length, stbi__zdefault_length, 288))
          return 0;
        if (!stbi__zbuild_huffman(&a->z_distance, stbi__zdefault_distance, 32))
          return 0;
      } else {
        if (!stbi__compute_huffman_codes(a)) return 0;
      }
      if (!stbi__parse_huffman_block(a)) return 0;
    }
  } while (!final);
  return 1;
}

static int stbi__do_zlib(stbi__zbuf *a, char *obuf, int olen, int exp,
                         int parse_header) {
  a->zout_start = obuf;
  a->zout = obuf;
  a->zout_end = obuf + olen;
  a->z_expandable = exp;

  return stbi__parse_zlib(a, parse_header);
}

char *stbi_zlib_decode_malloc_guesssize(const char *buffer, int len,
                                        int initial_size, int *outlen) {
  char *res, *p;
  stbi__zbuf *a;
  a = NULL;
  res = NULL;
  if ((p = (char *)malloc(initial_size)) &&
      (a = (stbi__zbuf *)malloc(sizeof(stbi__zbuf)))) {
    a->zbuffer = (unsigned char *)buffer;
    a->zbuffer_end = (unsigned char *)buffer + len;
    if (stbi__do_zlib(a, p, initial_size, 1, 1)) {
      if (outlen) *outlen = (int)(a->zout - a->zout_start);
      res = a->zout_start;
      a->zout_start = NULL;
    }
  }
  free(a->zout_start);
  free(a);
  return res;
}

char *stbi_zlib_decode_malloc(char const *buffer, int len, int *outlen) {
  return stbi_zlib_decode_malloc_guesssize(buffer, len, 16384, outlen);
}

char *stbi_zlib_decode_malloc_guesssize_headerflag(const char *buffer, int len,
                                                   int initial_size,
                                                   int *outlen,
                                                   int parse_header) {
  char *res;
  stbi__zbuf *a = malloc(sizeof(stbi__zbuf));
  char *p = (char *)malloc(initial_size);
  if (!p) return NULL;
  a->zbuffer = (unsigned char *)buffer;
  a->zbuffer_end = (unsigned char *)buffer + len;
  if (stbi__do_zlib(a, p, initial_size, 1, parse_header)) {
    if (outlen) *outlen = (int)(a->zout - a->zout_start);
    res = a->zout_start;
  } else {
    free(a->zout_start);
    res = NULL;
  }
  free(a);
  return res;
}

int stbi_zlib_decode_buffer(char *obuffer, int olen, char const *ibuffer,
                            int ilen) {
  stbi__zbuf a;
  a.zbuffer = (unsigned char *)ibuffer;
  a.zbuffer_end = (unsigned char *)ibuffer + ilen;
  if (stbi__do_zlib(&a, obuffer, olen, 0, 1))
    return (int)(a.zout - a.zout_start);
  else
    return -1;
}

char *stbi_zlib_decode_noheader_malloc(char const *buffer, int len,
                                       int *outlen) {
  stbi__zbuf a;
  char *p = (char *)malloc(16384);
  if (p == NULL) return NULL;
  a.zbuffer = (unsigned char *)buffer;
  a.zbuffer_end = (unsigned char *)buffer + len;
  if (stbi__do_zlib(&a, p, 16384, 1, 0)) {
    if (outlen) *outlen = (int)(a.zout - a.zout_start);
    return a.zout_start;
  } else {
    free(a.zout_start);
    return NULL;
  }
}

int stbi_zlib_decode_noheader_buffer(char *obuffer, int olen,
                                     const char *ibuffer, int ilen) {
  stbi__zbuf a;
  a.zbuffer = (unsigned char *)ibuffer;
  a.zbuffer_end = (unsigned char *)ibuffer + ilen;
  if (stbi__do_zlib(&a, obuffer, olen, 0, 0))
    return (int)(a.zout - a.zout_start);
  else
    return -1;
}

// public domain "baseline" PNG decoder   v0.10  Sean Barrett 2006-11-18
//    simple implementation
//      - only 8-bit samples
//      - no CRC checking
//      - allocates lots of intermediate memory
//        - avoids problem of streaming data between subsystems
//        - avoids explicit window management
//    performance
//      - uses stb_zlib, a PD zlib implementation with fast huffman decoding

typedef struct {
  uint32_t length;
  uint32_t type;
} stbi__pngchunk;

static stbi__pngchunk stbi__get_chunk_header(stbi__context *s) {
  stbi__pngchunk c;
  c.length = stbi__get32be(s);
  c.type = stbi__get32be(s);
  return c;
}

static int stbi__check_png_header(stbi__context *s) {
  int i;
  for (i = 0; i < 8; ++i) {
    if (stbi__get8(s) != kPngSig[i]) {
      return stbi__err("bad png sig", "Not a PNG");
    }
  }
  return 1;
}

typedef struct {
  stbi__context *s;
  unsigned char *idata, *expanded, *out;
  int depth;
} stbi__png;

enum {
  STBI__F_none = 0,
  STBI__F_sub = 1,
  STBI__F_up = 2,
  STBI__F_avg = 3,
  STBI__F_paeth = 4,
  // synthetic filters used for first scanline to avoid needing a dummy row of
  // 0s
  STBI__F_avg_first,
  STBI__F_paeth_first
};

static int stbi__de_iphone_flag = 0;
static int stbi__unpremultiply_on_load = 0;
static unsigned char first_row_filter[5] = {STBI__F_none, STBI__F_sub,
                                            STBI__F_none, STBI__F_avg_first,
                                            STBI__F_paeth_first};

static int stbi__paeth(int a, int b, int c) {
  int p = a + b - c;
  int pa = abs(p - a);
  int pb = abs(p - b);
  int pc = abs(p - c);
  if (pa <= pb && pa <= pc) return a;
  if (pb <= pc) return b;
  return c;
}

static const unsigned char stbi__depth_scale_table[9] = {
    0, 0xff, 0x55, 0, 0x11, 0, 0, 0, 0x01};

// create the png data from post-deflated data
static int stbi__create_png_image_raw(stbi__png *a, unsigned char *raw,
                                      uint32_t raw_len, int out_n, uint32_t x,
                                      uint32_t y, int depth, int color) {
  int bytes = (depth == 16 ? 2 : 1);
  stbi__context *s = a->s;
  uint32_t i, j, stride = x * out_n * bytes;
  uint32_t img_len, img_width_bytes;
  int k;
  int img_n = s->img_n;  // copy it into a local for later

  int output_bytes = out_n * bytes;
  int filter_bytes = img_n * bytes;
  int width = x;

  assert(out_n == s->img_n || out_n == s->img_n + 1);
  a->out = stbi__malloc_mad3(x, y, output_bytes,
                             0);  // extra bytes to write off the end into

  if (!stbi__mad3sizes_valid(img_n, x, depth, 7))
    return stbi__err("too large", "Corrupt PNG");
  img_width_bytes = (((img_n * x * depth) + 7) >> 3);
  img_len = (img_width_bytes + 1) * y;

  // we used to check for exact match between raw_len and img_len on
  // non-interlaced PNGs, but issue #276 reported a PNG in the wild that had
  // extra data at the end (all zeros), so just check for raw_len < img_len
  // always.
  if (raw_len < img_len) return stbi__err("not enough pixels", "Corrupt PNG");

  for (j = 0; j < y; ++j) {
    unsigned char *cur = a->out + stride * j;
    unsigned char *prior;
    int filter = *raw++;

    if (filter > 4) return stbi__err("invalid filter", "Corrupt PNG");

    if (depth < 8) {
      assert(img_width_bytes <= x);
      cur +=
          x * out_n - img_width_bytes;  // store output to the rightmost img_len
      // bytes, so we can decode in place
      filter_bytes = 1;
      width = img_width_bytes;
    }
    prior = cur - stride;  // bugfix: need to compute this after 'cur +='
    // computation above

    // if first row, use special filter that doesn't sample previous row
    if (j == 0) filter = first_row_filter[filter];

    // handle first byte explicitly
    for (k = 0; k < filter_bytes; ++k) {
      switch (filter) {
        case STBI__F_none:
          cur[k] = raw[k];
          break;
        case STBI__F_sub:
          cur[k] = raw[k];
          break;
        case STBI__F_up:
          cur[k] = STBI__BYTECAST(raw[k] + prior[k]);
          break;
        case STBI__F_avg:
          cur[k] = STBI__BYTECAST(raw[k] + (prior[k] >> 1));
          break;
        case STBI__F_paeth:
          cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(0, prior[k], 0));
          break;
        case STBI__F_avg_first:
          cur[k] = raw[k];
          break;
        case STBI__F_paeth_first:
          cur[k] = raw[k];
          break;
      }
    }

    if (depth == 8) {
      if (img_n != out_n) cur[img_n] = 255;  // first pixel
      raw += img_n;
      cur += out_n;
      prior += out_n;
    } else if (depth == 16) {
      if (img_n != out_n) {
        cur[filter_bytes] = 255;      // first pixel top byte
        cur[filter_bytes + 1] = 255;  // first pixel bottom byte
      }
      raw += filter_bytes;
      cur += output_bytes;
      prior += output_bytes;
    } else {
      raw += 1;
      cur += 1;
      prior += 1;
    }

    // this is a little gross, so that we don't switch per-pixel or
    // per-component
    if (depth < 8 || img_n == out_n) {
      int nk = (width - 1) * filter_bytes;
#define STBI__CASE(f) \
  case f:             \
    for (k = 0; k < nk; ++k)
      switch (filter) {
        // "none" filter turns into a memcpy here; make that explicit.
        case STBI__F_none:
          memcpy(cur, raw, nk);
          break;
          STBI__CASE(STBI__F_sub) {
            cur[k] = STBI__BYTECAST(raw[k] + cur[k - filter_bytes]);
          }
          break;
          STBI__CASE(STBI__F_up) {
            cur[k] = STBI__BYTECAST(raw[k] + prior[k]);
          }
          break;
          STBI__CASE(STBI__F_avg) {
            cur[k] = STBI__BYTECAST(raw[k] +
                                    ((prior[k] + cur[k - filter_bytes]) >> 1));
          }
          break;
          STBI__CASE(STBI__F_paeth) {
            cur[k] = STBI__BYTECAST(raw[k] +
                                    stbi__paeth(cur[k - filter_bytes], prior[k],
                                                prior[k - filter_bytes]));
          }
          break;
          STBI__CASE(STBI__F_avg_first) {
            cur[k] = STBI__BYTECAST(raw[k] + (cur[k - filter_bytes] >> 1));
          }
          break;
          STBI__CASE(STBI__F_paeth_first) {
            cur[k] = STBI__BYTECAST(raw[k] +
                                    stbi__paeth(cur[k - filter_bytes], 0, 0));
          }
          break;
      }
#undef STBI__CASE
      raw += nk;
    } else {
      assert(img_n + 1 == out_n);
#define STBI__CASE(f)                                                          \
  case f:                                                                      \
    for (i = x - 1; i >= 1; --i, cur[filter_bytes] = 255, raw += filter_bytes, \
        cur += output_bytes, prior += output_bytes)                            \
      for (k = 0; k < filter_bytes; ++k)
      switch (filter) {
        STBI__CASE(STBI__F_none) {
          cur[k] = raw[k];
        }
        break;
        STBI__CASE(STBI__F_sub) {
          cur[k] = STBI__BYTECAST(raw[k] + cur[k - output_bytes]);
        }
        break;
        STBI__CASE(STBI__F_up) {
          cur[k] = STBI__BYTECAST(raw[k] + prior[k]);
        }
        break;
        STBI__CASE(STBI__F_avg) {
          cur[k] = STBI__BYTECAST(raw[k] +
                                  ((prior[k] + cur[k - output_bytes]) >> 1));
        }
        break;
        STBI__CASE(STBI__F_paeth) {
          cur[k] = STBI__BYTECAST(raw[k] +
                                  stbi__paeth(cur[k - output_bytes], prior[k],
                                              prior[k - output_bytes]));
        }
        break;
        STBI__CASE(STBI__F_avg_first) {
          cur[k] = STBI__BYTECAST(raw[k] + (cur[k - output_bytes] >> 1));
        }
        break;
        STBI__CASE(STBI__F_paeth_first) {
          cur[k] =
              STBI__BYTECAST(raw[k] + stbi__paeth(cur[k - output_bytes], 0, 0));
        }
        break;
      }
#undef STBI__CASE

      // the loop above sets the high byte of the pixels' alpha, but for
      // 16 bit png files we also need the low byte set. we'll do that here.
      if (depth == 16) {
        cur = a->out + stride * j;  // start at the beginning of the row again
        for (i = 0; i < x; ++i, cur += output_bytes) {
          cur[filter_bytes + 1] = 255;
        }
      }
    }
  }

  // we make a separate pass to expand bits to pixels; for performance,
  // this could run two scanlines behind the above code, so it won't
  // intefere with filtering but will still be in the cache.
  if (depth < 8) {
    for (j = 0; j < y; ++j) {
      unsigned char *cur = a->out + stride * j;
      unsigned char *in = a->out + stride * j + x * out_n - img_width_bytes;
      // unpack 1/2/4-bit into a 8-bit buffer. allows us to keep the common
      // 8-bit path optimal at minimal cost for 1/2/4-bit png guarante byte
      // alignment, if width is not multiple of 8/4/2 we'll decode dummy
      // trailing data that will be skipped in the later loop
      unsigned char scale = (color == 0)
                                ? stbi__depth_scale_table[depth]
                                : 1;  // scale grayscale values to 0..255 range

      // note that the final byte might overshoot and write more data than
      // desired. we can allocate enough data that this never writes out of
      // memory, but it could also overwrite the next scanline. can it
      // overwrite non-empty data on the next scanline? yes, consider
      // 1-pixel-wide scanlines with 1-bit-per-pixel. so we need to explicitly
      // clamp the final ones

      if (depth == 4) {
        for (k = x * img_n; k >= 2; k -= 2, ++in) {
          *cur++ = scale * ((*in >> 4));
          *cur++ = scale * ((*in) & 0x0f);
        }
        if (k > 0) *cur++ = scale * ((*in >> 4));
      } else if (depth == 2) {
        for (k = x * img_n; k >= 4; k -= 4, ++in) {
          *cur++ = scale * ((*in >> 6));
          *cur++ = scale * ((*in >> 4) & 0x03);
          *cur++ = scale * ((*in >> 2) & 0x03);
          *cur++ = scale * ((*in) & 0x03);
        }
        if (k > 0) *cur++ = scale * ((*in >> 6));
        if (k > 1) *cur++ = scale * ((*in >> 4) & 0x03);
        if (k > 2) *cur++ = scale * ((*in >> 2) & 0x03);
      } else if (depth == 1) {
        for (k = x * img_n; k >= 8; k -= 8, ++in) {
          *cur++ = scale * ((*in >> 7));
          *cur++ = scale * ((*in >> 6) & 0x01);
          *cur++ = scale * ((*in >> 5) & 0x01);
          *cur++ = scale * ((*in >> 4) & 0x01);
          *cur++ = scale * ((*in >> 3) & 0x01);
          *cur++ = scale * ((*in >> 2) & 0x01);
          *cur++ = scale * ((*in >> 1) & 0x01);
          *cur++ = scale * ((*in) & 0x01);
        }
        if (k > 0) *cur++ = scale * ((*in >> 7));
        if (k > 1) *cur++ = scale * ((*in >> 6) & 0x01);
        if (k > 2) *cur++ = scale * ((*in >> 5) & 0x01);
        if (k > 3) *cur++ = scale * ((*in >> 4) & 0x01);
        if (k > 4) *cur++ = scale * ((*in >> 3) & 0x01);
        if (k > 5) *cur++ = scale * ((*in >> 2) & 0x01);
        if (k > 6) *cur++ = scale * ((*in >> 1) & 0x01);
      }
      if (img_n != out_n) {
        int q;
        // insert alpha = 255
        cur = a->out + stride * j;
        if (img_n == 1) {
          for (q = x - 1; q >= 0; --q) {
            cur[q * 2 + 1] = 255;
            cur[q * 2 + 0] = cur[q];
          }
        } else {
          assert(img_n == 3);
          for (q = x - 1; q >= 0; --q) {
            cur[q * 4 + 3] = 255;
            cur[q * 4 + 2] = cur[q * 3 + 2];
            cur[q * 4 + 1] = cur[q * 3 + 1];
            cur[q * 4 + 0] = cur[q * 3 + 0];
          }
        }
      }
    }
  } else if (depth == 16) {
    // force the image data from big-endian to platform-native.
    // this is done in a separate pass due to the decoding relying
    // on the data being untouched, but could probably be done
    // per-line during decode if care is taken.
    unsigned char *cur = a->out;
    uint16_t *cur16 = (uint16_t *)cur;

    for (i = 0; i < x * y * out_n; ++i, cur16++, cur += 2) {
      *cur16 = (cur[0] << 8) | cur[1];
    }
  }

  return 1;
}

static int stbi__create_png_image(stbi__png *a, unsigned char *image_data,
                                  uint32_t image_data_len, int out_n, int depth,
                                  int color, int interlaced) {
  int bytes = (depth == 16 ? 2 : 1);
  int out_bytes = out_n * bytes;
  unsigned char *final;
  int p;
  if (!interlaced)
    return stbi__create_png_image_raw(a, image_data, image_data_len, out_n,
                                      a->s->img_x, a->s->img_y, depth, color);
  // de-interlacing
  final = stbi__malloc_mad3(a->s->img_x, a->s->img_y, out_bytes, 0);
  for (p = 0; p < 7; ++p) {
    int xorig[] = {0, 4, 0, 2, 0, 1, 0};
    int yorig[] = {0, 0, 4, 0, 2, 0, 1};
    int xspc[] = {8, 8, 4, 4, 2, 2, 1};
    int yspc[] = {8, 8, 8, 4, 4, 2, 2};
    int i, j, x, y;
    // pass1_x[4] = 0, pass1_x[5] = 1, pass1_x[12] = 1
    x = (a->s->img_x - xorig[p] + xspc[p] - 1) / xspc[p];
    y = (a->s->img_y - yorig[p] + yspc[p] - 1) / yspc[p];
    if (x && y) {
      uint32_t img_len = ((((a->s->img_n * x * depth) + 7) >> 3) + 1) * y;
      if (!stbi__create_png_image_raw(a, image_data, image_data_len, out_n, x,
                                      y, depth, color)) {
        free(final);
        return 0;
      }
      for (j = 0; j < y; ++j) {
        for (i = 0; i < x; ++i) {
          int out_y = j * yspc[p] + yorig[p];
          int out_x = i * xspc[p] + xorig[p];
          memcpy(final + out_y * a->s->img_x * out_bytes + out_x * out_bytes,
                 a->out + (j * x + i) * out_bytes, out_bytes);
        }
      }
      free(a->out);
      image_data += img_len;
      image_data_len -= img_len;
    }
  }
  a->out = final;
  return 1;
}

static int stbi__compute_transparency(stbi__png *z, unsigned char tc[3],
                                      int out_n) {
  stbi__context *s = z->s;
  uint32_t i, pixel_count = s->img_x * s->img_y;
  unsigned char *p = z->out;
  // compute color-based transparency, assuming we've
  // already got 255 as the alpha value in the output
  assert(out_n == 2 || out_n == 4);
  if (out_n == 2) {
    for (i = 0; i < pixel_count; ++i) {
      p[1] = (p[0] == tc[0] ? 0 : 255);
      p += 2;
    }
  } else {
    for (i = 0; i < pixel_count; ++i) {
      if (p[0] == tc[0] && p[1] == tc[1] && p[2] == tc[2]) p[3] = 0;
      p += 4;
    }
  }
  return 1;
}

static int stbi__compute_transparency16(stbi__png *z, uint16_t tc[3],
                                        int out_n) {
  stbi__context *s = z->s;
  uint32_t i, pixel_count = s->img_x * s->img_y;
  uint16_t *p = (uint16_t *)z->out;
  // compute color-based transparency, assuming we've
  // already got 65535 as the alpha value in the output
  assert(out_n == 2 || out_n == 4);
  if (out_n == 2) {
    for (i = 0; i < pixel_count; ++i) {
      p[1] = (p[0] == tc[0] ? 0 : 65535);
      p += 2;
    }
  } else {
    for (i = 0; i < pixel_count; ++i) {
      if (p[0] == tc[0] && p[1] == tc[1] && p[2] == tc[2]) p[3] = 0;
      p += 4;
    }
  }
  return 1;
}

static int stbi__expand_png_palette(stbi__png *a, unsigned char *palette,
                                    int len, int pal_img_n) {
  uint32_t i, pixel_count = a->s->img_x * a->s->img_y;
  unsigned char *p, *temp_out, *orig = a->out;
  p = stbi__malloc_mad2(pixel_count, pal_img_n, 0);
  // between here and free(out) below, exitting would leak
  temp_out = p;
  if (pal_img_n == 3) {
    for (i = 0; i < pixel_count; ++i) {
      int n = orig[i] * 4;
      p[0] = palette[n];
      p[1] = palette[n + 1];
      p[2] = palette[n + 2];
      p += 3;
    }
  } else {
    for (i = 0; i < pixel_count; ++i) {
      int n = orig[i] * 4;
      p[0] = palette[n];
      p[1] = palette[n + 1];
      p[2] = palette[n + 2];
      p[3] = palette[n + 3];
      p += 4;
    }
  }
  free(a->out);
  a->out = temp_out;
  return 1;
}

void stbi_set_unpremultiply_on_load(int flag_true_if_should_unpremultiply) {
  stbi__unpremultiply_on_load = flag_true_if_should_unpremultiply;
}

void stbi_convert_iphone_png_to_rgb(int flag_true_if_should_convert) {
  stbi__de_iphone_flag = flag_true_if_should_convert;
}

static void stbi__de_iphone(stbi__png *z) {
  stbi__context *s = z->s;
  uint32_t i, pixel_count = s->img_x * s->img_y;
  unsigned char *p = z->out;
  if (s->img_out_n == 3) {  // convert bgr to rgb
    for (i = 0; i < pixel_count; ++i) {
      unsigned char t = p[0];
      p[0] = p[2];
      p[2] = t;
      p += 3;
    }
  } else {
    assert(s->img_out_n == 4);
    if (stbi__unpremultiply_on_load) {
      // convert bgr to rgb and unpremultiply
      for (i = 0; i < pixel_count; ++i) {
        unsigned char a = p[3];
        unsigned char t = p[0];
        if (a) {
          unsigned char half = a / 2;
          p[0] = (p[2] * 255 + half) / a;
          p[1] = (p[1] * 255 + half) / a;
          p[2] = (t * 255 + half) / a;
        } else {
          p[0] = p[2];
          p[2] = t;
        }
        p += 4;
      }
    } else {
      // convert bgr to rgb
      for (i = 0; i < pixel_count; ++i) {
        unsigned char t = p[0];
        p[0] = p[2];
        p[2] = t;
        p += 4;
      }
    }
  }
}

#define STBI__PNG_TYPE(a, b, c, d)                                        \
  (((unsigned)(a) << 24) + ((unsigned)(b) << 16) + ((unsigned)(c) << 8) + \
   (unsigned)(d))

static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp) {
  unsigned char palette[1024], pal_img_n = 0;
  unsigned char has_trans = 0, tc[3] = {0};
  uint16_t tc16[3];
  uint32_t ioff = 0, idata_limit = 0, i, pal_len = 0;
  int first = 1, k, interlace = 0, color = 0, is_iphone = 0;
  stbi__context *s = z->s;
  z->expanded = NULL;
  z->idata = NULL;
  z->out = NULL;
  if (!stbi__check_png_header(s)) return 0;
  if (scan == STBI__SCAN_type) return 1;
  for (;;) {
    stbi__pngchunk c = stbi__get_chunk_header(s);
    switch (c.type) {

      case STBI__PNG_TYPE('C', 'g', 'B', 'I'):
        is_iphone = 1;
        stbi__skip(s, c.length);
        break;

      case STBI__PNG_TYPE('I', 'H', 'D', 'R'): {
        int comp, filter;
        if (!first) return stbi__err("multiple IHDR", "Corrupt PNG");
        first = 0;
        if (c.length != 13) return stbi__err("bad IHDR len", "Corrupt PNG");
        s->img_x = stbi__get32be(s);
        if (s->img_x > (1 << 24))
          return stbi__err("too large", "Very large image (corrupt?)");
        s->img_y = stbi__get32be(s);
        if (s->img_y > (1 << 24))
          return stbi__err("too large", "Very large image (corrupt?)");
        z->depth = stbi__get8(s);
        if (z->depth != 1 && z->depth != 2 && z->depth != 4 && z->depth != 8 &&
            z->depth != 16)
          return stbi__err("1/2/4/8/16-bit only",
                           "PNG not supported: 1/2/4/8/16-bit only");
        color = stbi__get8(s);
        if (color > 6) return stbi__err("bad ctype", "Corrupt PNG");
        if (color == 3 && z->depth == 16)
          return stbi__err("bad ctype", "Corrupt PNG");
        if (color == 3)
          pal_img_n = 3;
        else if (color & 1)
          return stbi__err("bad ctype", "Corrupt PNG");
        comp = stbi__get8(s);
        if (comp) return stbi__err("bad comp method", "Corrupt PNG");
        filter = stbi__get8(s);
        if (filter) return stbi__err("bad filter method", "Corrupt PNG");
        interlace = stbi__get8(s);
        if (interlace > 1)
          return stbi__err("bad interlace method", "Corrupt PNG");
        if (!s->img_x || !s->img_y)
          return stbi__err("0-pixel image", "Corrupt PNG");
        if (!pal_img_n) {
          s->img_n = (color & 2 ? 3 : 1) + (color & 4 ? 1 : 0);
          if ((1 << 30) / s->img_x / s->img_n < s->img_y)
            return stbi__err("too large", "Image too large to decode");
          if (scan == STBI__SCAN_header) return 1;
        } else {
          // if paletted, then pal_n is our final components, and
          // img_n is # components to decompress/filter.
          s->img_n = 1;
          if ((1 << 30) / s->img_x / 4 < s->img_y)
            return stbi__err("too large", "Corrupt PNG");
          // if SCAN_header, have to scan to see if we have a tRNS
        }
        break;
      }

      case STBI__PNG_TYPE('P', 'L', 'T', 'E'): {
        if (first) return stbi__err("first not IHDR", "Corrupt PNG");
        if (c.length > 256 * 3) return stbi__err("invalid PLTE", "Corrupt PNG");
        pal_len = c.length / 3;
        if (pal_len * 3 != c.length)
          return stbi__err("invalid PLTE", "Corrupt PNG");
        for (i = 0; i < pal_len; ++i) {
          palette[i * 4 + 0] = stbi__get8(s);
          palette[i * 4 + 1] = stbi__get8(s);
          palette[i * 4 + 2] = stbi__get8(s);
          palette[i * 4 + 3] = 255;
        }
        break;
      }

      case STBI__PNG_TYPE('t', 'R', 'N', 'S'): {
        if (first) return stbi__err("first not IHDR", "Corrupt PNG");
        if (z->idata) return stbi__err("tRNS after IDAT", "Corrupt PNG");
        if (pal_img_n) {
          if (scan == STBI__SCAN_header) {
            s->img_n = 4;
            return 1;
          }
          if (pal_len == 0) return stbi__err("tRNS before PLTE", "Corrupt PNG");
          if (c.length > pal_len)
            return stbi__err("bad tRNS len", "Corrupt PNG");
          pal_img_n = 4;
          for (i = 0; i < c.length; ++i) palette[i * 4 + 3] = stbi__get8(s);
        } else {
          if (!(s->img_n & 1))
            return stbi__err("tRNS with alpha", "Corrupt PNG");
          if (c.length != (uint32_t)s->img_n * 2)
            return stbi__err("bad tRNS len", "Corrupt PNG");
          has_trans = 1;
          if (z->depth == 16) {
            for (k = 0; k < s->img_n; ++k)
              tc16[k] = (uint16_t)stbi__get16be(s);  // copy the values as-is
          } else {
            for (k = 0; k < s->img_n; ++k)
              tc[k] = (unsigned char)(stbi__get16be(s) & 255) *
                      stbi__depth_scale_table[z->depth];  // non 8-bit images
                                                          // will be larger
          }
        }
        break;
      }

      case STBI__PNG_TYPE('I', 'D', 'A', 'T'): {
        if (first) return stbi__err("first not IHDR", "Corrupt PNG");
        if (pal_img_n && !pal_len) return stbi__err("no PLTE", "Corrupt PNG");
        if (scan == STBI__SCAN_header) {
          s->img_n = pal_img_n;
          return 1;
        }
        if ((int)(ioff + c.length) < (int)ioff) return 0;
        if (ioff + c.length > idata_limit) {
          uint32_t idata_limit_old = idata_limit;
          unsigned char *p;
          if (idata_limit == 0) idata_limit = c.length > 4096 ? c.length : 4096;
          while (ioff + c.length > idata_limit) idata_limit *= 2;
          (void)idata_limit_old;
          p = STBI_REALLOC_SIZED(z->idata, idata_limit_old, idata_limit);
          if (p == NULL) return stbi__err("outofmem", "Out of memory");
          z->idata = p;
        }
        if (!stbi__getn(s, z->idata + ioff, c.length))
          return stbi__err("outofdata", "Corrupt PNG");
        ioff += c.length;
        break;
      }

      case STBI__PNG_TYPE('I', 'E', 'N', 'D'): {
        uint32_t raw_len, bpl;
        if (first) return stbi__err("first not IHDR", "Corrupt PNG");
        if (scan != STBI__SCAN_load) return 1;
        if (z->idata == NULL) return stbi__err("no IDAT", "Corrupt PNG");
        // initial guess for decoded data size to avoid unnecessary reallocs
        bpl = (s->img_x * z->depth + 7) / 8;  // bytes per line, per component
        raw_len = bpl * s->img_y * s->img_n /* pixels */ +
                  s->img_y /* filter mode per row */;
        z->expanded =
            (unsigned char *)stbi_zlib_decode_malloc_guesssize_headerflag(
                (char *)z->idata, ioff, raw_len, (int *)&raw_len, !is_iphone);
        if (z->expanded == NULL) return 0;  // zlib should set error
        free(z->idata);
        z->idata = NULL;
        if ((req_comp == s->img_n + 1 && req_comp != 3 && !pal_img_n) ||
            has_trans) {
          s->img_out_n = s->img_n + 1;
        } else {
          s->img_out_n = s->img_n;
        }
        if (!stbi__create_png_image(z, z->expanded, raw_len, s->img_out_n,
                                    z->depth, color, interlace))
          return 0;
        if (has_trans) {
          if (z->depth == 16) {
            if (!stbi__compute_transparency16(z, tc16, s->img_out_n)) return 0;
          } else {
            if (!stbi__compute_transparency(z, tc, s->img_out_n)) return 0;
          }
        }
        if (is_iphone && stbi__de_iphone_flag && s->img_out_n > 2)
          stbi__de_iphone(z);
        if (pal_img_n) {
          // pal_img_n == 3 or 4
          s->img_n = pal_img_n;  // record the actual colors we had
          s->img_out_n = pal_img_n;
          if (req_comp >= 3) s->img_out_n = req_comp;
          if (!stbi__expand_png_palette(z, palette, pal_len, s->img_out_n))
            return 0;
        } else if (has_trans) {
          // non-paletted image with tRNS -> source image has (constant) alpha
          ++s->img_n;
        }
        free(z->expanded);
        z->expanded = NULL;
        stbi__get32be(s); /* nothings/stb#835 */
        return 1;
      }

      default:
        // if critical, fail
        if (first) return stbi__err("first not IHDR", "Corrupt PNG");
        if ((c.type & (1 << 29)) == 0) {
#ifndef STBI_NO_FAILURE_STRINGS
          // not threadsafe
          static char invalid_chunk[] = "XXXX PNG chunk not known";
          invalid_chunk[0] = STBI__BYTECAST(c.type >> 24);
          invalid_chunk[1] = STBI__BYTECAST(c.type >> 16);
          invalid_chunk[2] = STBI__BYTECAST(c.type >> 8);
          invalid_chunk[3] = STBI__BYTECAST(c.type >> 0);
#endif
          return stbi__err(invalid_chunk,
                           "PNG not supported: unknown PNG chunk type");
        }
        stbi__skip(s, c.length);
        break;
    }
    // end of PNG chunk, read and skip CRC
    stbi__get32be(s);
  }
}

static void *stbi__do_png(stbi__png *p, int *x, int *y, int *n, int req_comp,
                          stbi__result_info *ri) {
  void *result = NULL;
  if (req_comp < 0 || req_comp > 4)
    return stbi__errpuc("bad req_comp", "Internal error");
  if (stbi__parse_png_file(p, STBI__SCAN_load, req_comp)) {
    if (p->depth < 8)
      ri->bits_per_channel = 8;
    else
      ri->bits_per_channel = p->depth;
    result = p->out;
    p->out = NULL;
    if (req_comp && req_comp != p->s->img_out_n) {
      if (ri->bits_per_channel == 8)
        result = stbi__convert_format((unsigned char *)result, p->s->img_out_n,
                                      req_comp, p->s->img_x, p->s->img_y);
      else
        result = stbi__convert_format16((uint16_t *)result, p->s->img_out_n,
                                        req_comp, p->s->img_x, p->s->img_y);
      p->s->img_out_n = req_comp;
      if (result == NULL) return result;
    }
    *x = p->s->img_x;
    *y = p->s->img_y;
    if (n) *n = p->s->img_n;
  }
  free(p->out);
  p->out = NULL;
  free(p->expanded);
  p->expanded = NULL;
  free(p->idata);
  p->idata = NULL;

  return result;
}

static noinline void *stbi__png_load(stbi__context *s, int *x, int *y,
                                     int *comp, int req_comp,
                                     stbi__result_info *ri) {
  stbi__png p;
  p.s = s;
  return stbi__do_png(&p, x, y, comp, req_comp, ri);
}

static int stbi__png_test(stbi__context *s) {
  int r;
  r = stbi__check_png_header(s);
  stbi__rewind(s);
  return r;
}

static int stbi__png_info_raw(stbi__png *p, int *x, int *y, int *comp) {
  if (!stbi__parse_png_file(p, STBI__SCAN_header, 0)) {
    stbi__rewind(p->s);
    return 0;
  }
  if (x) *x = p->s->img_x;
  if (y) *y = p->s->img_y;
  if (comp) *comp = p->s->img_n;
  return 1;
}

static int stbi__png_info(stbi__context *s, int *x, int *y, int *comp) {
  stbi__png p;
  p.s = s;
  return stbi__png_info_raw(&p, x, y, comp);
}

static int stbi__png_is16(stbi__context *s) {
  stbi__png p;
  p.s = s;
  if (!stbi__png_info_raw(&p, NULL, NULL, NULL)) return 0;
  if (p.depth != 16) {
    stbi__rewind(p.s);
    return 0;
  }
  return 1;
}

// *****************************************************************************
// GIF loader -- public domain by Jean-Marc Lienher -- simplified/shrunk by
// stb

typedef struct {
  int16_t prefix;
  unsigned char first;
  unsigned char suffix;
} stbi__gif_lzw;

typedef struct {
  int w, h;
  unsigned char *out;  // output buffer (always 4 components)
  unsigned char
      *background;  // The current "background" as far as a gif is concerned
  unsigned char *history;
  int flags, bgindex, ratio, transparent, eflags;
  unsigned char pal[256][4];
  unsigned char lpal[256][4];
  stbi__gif_lzw codes[8192];
  unsigned char *color_table;
  int parse, step;
  int lflags;
  int start_x, start_y;
  int max_x, max_y;
  int cur_x, cur_y;
  int line_size;
  int delay;
} stbi__gif;

static int stbi__gif_test_raw(stbi__context *s) {
  int sz;
  if (stbi__get8(s) != 'G' || stbi__get8(s) != 'I' || stbi__get8(s) != 'F' ||
      stbi__get8(s) != '8')
    return 0;
  sz = stbi__get8(s);
  if (sz != '9' && sz != '7') return 0;
  if (stbi__get8(s) != 'a') return 0;
  return 1;
}

static int stbi__gif_test(stbi__context *s) {
  int r = stbi__gif_test_raw(s);
  stbi__rewind(s);
  return r;
}

static void stbi__gif_parse_colortable(stbi__context *s,
                                       unsigned char pal[256][4],
                                       int num_entries, int transp) {
  int i;
  for (i = 0; i < num_entries; ++i) {
    pal[i][2] = stbi__get8(s);
    pal[i][1] = stbi__get8(s);
    pal[i][0] = stbi__get8(s);
    pal[i][3] = transp == i ? 0 : 255;
  }
}

static int stbi__gif_header(stbi__context *s, stbi__gif *g, int *comp,
                            int is_info) {
  unsigned char version;
  if (stbi__get8(s) != 'G' || stbi__get8(s) != 'I' || stbi__get8(s) != 'F' ||
      stbi__get8(s) != '8')
    return stbi__err("not GIF", "Corrupt GIF");
  version = stbi__get8(s);
  if (version != '7' && version != '9') {
    return stbi__err("not GIF", "Corrupt GIF");
  }
  if (stbi__get8(s) != 'a') return stbi__err("not GIF", "Corrupt GIF");
  stbi__g_failure_reason = "";
  g->w = stbi__get16le(s);
  g->h = stbi__get16le(s);
  g->flags = stbi__get8(s);
  g->bgindex = stbi__get8(s);
  g->ratio = stbi__get8(s);
  g->transparent = -1;
  if (comp != 0) {
    *comp = 4;  // can't actually tell whether it's 3 or 4 until we parse the
                // comments
  }
  if (is_info) return 1;
  if (g->flags & 0x80) {
    stbi__gif_parse_colortable(s, g->pal, 2 << (g->flags & 7), -1);
  }
  return 1;
}

static int stbi__gif_info_raw(stbi__context *s, int *x, int *y, int *comp) {
  stbi__gif *g = (stbi__gif *)malloc(sizeof(stbi__gif));
  if (!stbi__gif_header(s, g, comp, 1)) {
    free(g);
    stbi__rewind(s);
    return 0;
  }
  if (x) *x = g->w;
  if (y) *y = g->h;
  free(g);
  return 1;
}

static void stbi__out_gif_code(stbi__gif *g, uint16_t code) {
  unsigned char *p, *c;
  int idx;
  // recurse to decode the prefixes, since the linked-list is backwards,
  // and working backwards through an interleaved image would be nasty
  if (g->codes[code].prefix >= 0) stbi__out_gif_code(g, g->codes[code].prefix);
  if (g->cur_y >= g->max_y) return;
  idx = g->cur_x + g->cur_y;
  p = &g->out[idx];
  g->history[idx / 4] = 1;
  c = &g->color_table[g->codes[code].suffix * 4];
  if (c[3] > 128) {  // don't render transparent pixels;
    p[0] = c[2];
    p[1] = c[1];
    p[2] = c[0];
    p[3] = c[3];
  }
  g->cur_x += 4;
  if (g->cur_x >= g->max_x) {
    g->cur_x = g->start_x;
    g->cur_y += g->step;
    while (g->cur_y >= g->max_y && g->parse > 0) {
      g->step = (1 << g->parse) * g->line_size;
      g->cur_y = g->start_y + (g->step >> 1);
      --g->parse;
    }
  }
}

static unsigned char *stbi__process_gif_raster(stbi__context *s, stbi__gif *g) {
  unsigned char lzw_cs;
  int32_t len, init_code;
  uint32_t first;
  int32_t codesize, codemask, avail, oldcode, bits, valid_bits, clear;
  stbi__gif_lzw *p;

  lzw_cs = stbi__get8(s);
  if (lzw_cs > 12) return NULL;
  clear = 1 << lzw_cs;
  first = 1;
  codesize = lzw_cs + 1;
  codemask = (1 << codesize) - 1;
  bits = 0;
  valid_bits = 0;
  for (init_code = 0; init_code < clear; init_code++) {
    g->codes[init_code].prefix = -1;
    g->codes[init_code].first = (unsigned char)init_code;
    g->codes[init_code].suffix = (unsigned char)init_code;
  }

  // support no starting clear code
  avail = clear + 2;
  oldcode = -1;

  len = 0;
  for (;;) {
    if (valid_bits < codesize) {
      if (len == 0) {
        len = stbi__get8(s);  // start new block
        if (len == 0) return g->out;
      }
      --len;
      bits |= (int32_t)stbi__get8(s) << valid_bits;
      valid_bits += 8;
    } else {
      int32_t code = bits & codemask;
      bits >>= codesize;
      valid_bits -= codesize;
      // @OPTIMIZE: is there some way we can accelerate the non-clear path?
      if (code == clear) {  // clear code
        codesize = lzw_cs + 1;
        codemask = (1 << codesize) - 1;
        avail = clear + 2;
        oldcode = -1;
        first = 0;
      } else if (code == clear + 1) {  // end of stream code
        stbi__skip(s, len);
        while ((len = stbi__get8(s)) > 0) stbi__skip(s, len);
        return g->out;
      } else if (code <= avail) {
        if (first) {
          return stbi__errpuc("no clear code", "Corrupt GIF");
        }

        if (oldcode >= 0) {
          p = &g->codes[avail++];
          if (avail > 8192) {
            return stbi__errpuc("too many codes", "Corrupt GIF");
          }

          p->prefix = (int16_t)oldcode;
          p->first = g->codes[oldcode].first;
          p->suffix = (code == avail) ? p->first : g->codes[code].first;
        } else if (code == avail)
          return stbi__errpuc("illegal code in raster", "Corrupt GIF");

        stbi__out_gif_code(g, (uint16_t)code);

        if ((avail & codemask) == 0 && avail <= 0x0FFF) {
          codesize++;
          codemask = (1 << codesize) - 1;
        }

        oldcode = code;
      } else {
        return stbi__errpuc("illegal code in raster", "Corrupt GIF");
      }
    }
  }
}

// this function is designed to support animated gifs, although stb_image
// doesn't support it two back is the image from two frames ago, used for a
// very specific disposal format
static unsigned char *stbi__gif_load_next(stbi__context *s, stbi__gif *g,
                                          int *comp, int req_comp,
                                          unsigned char *two_back) {
  int dispose;
  int first_frame;
  int pi;
  int pcount;

  // on first frame, any non-written pixels get the background colour
  // (non-transparent)
  first_frame = 0;
  if (g->out == 0) {
    if (!stbi__gif_header(s, g, comp, 0))
      return 0;  // stbi__g_failure_reason set by stbi__gif_header
    if (!stbi__mad3sizes_valid(4, g->w, g->h, 0))
      return stbi__errpuc("too large", "GIF image is too large");
    pcount = g->w * g->h;
    g->out = malloc(4 * pcount);
    g->background = malloc(4 * pcount);
    g->history = malloc(pcount);
    if (!g->out || !g->background || !g->history)
      return stbi__errpuc("outofmem", "Out of memory");

    // image is treated as "transparent" at the start - ie, nothing overwrites
    // the current background; background colour is only used for pixels that
    // are not rendered first frame, after that "background" color refers to
    // the color that was there the previous frame.
    bzero(g->out, 4 * pcount);
    bzero(g->background,
          4 * pcount);  // state of the background (starts transparent)
    bzero(g->history,
          pcount);  // pixels that were affected previous frame
    first_frame = 1;
  } else {
    // second frame - how do we dispoase of the previous one?
    dispose = (g->eflags & 0x1C) >> 2;
    pcount = g->w * g->h;

    if ((dispose == 3) && (two_back == 0)) {
      dispose = 2;  // if I don't have an image to revert back to, default to
                    // the old background
    }

    if (dispose == 3) {  // use previous graphic
      for (pi = 0; pi < pcount; ++pi) {
        if (g->history[pi]) {
          memcpy(&g->out[pi * 4], &two_back[pi * 4], 4);
        }
      }
    } else if (dispose == 2) {
      // restore what was changed last frame to background before that frame;
      for (pi = 0; pi < pcount; ++pi) {
        if (g->history[pi]) {
          memcpy(&g->out[pi * 4], &g->background[pi * 4], 4);
        }
      }
    } else {
      // This is a non-disposal case eithe way, so just
      // leave the pixels as is, and they will become the new background
      // 1: do not dispose
      // 0:  not specified.
    }

    // background is what out is after the undoing of the previou frame;
    memcpy(g->background, g->out, 4 * g->w * g->h);
  }

  // clear my history;
  bzero(g->history,
        g->w * g->h);  // pixels that were affected previous frame

  for (;;) {
    int tag = stbi__get8(s);
    switch (tag) {
      case 0x2C: /* Image Descriptor */
      {
        int32_t x, y, w, h;
        unsigned char *o;

        x = stbi__get16le(s);
        y = stbi__get16le(s);
        w = stbi__get16le(s);
        h = stbi__get16le(s);
        if (((x + w) > (g->w)) || ((y + h) > (g->h)))
          return stbi__errpuc("bad Image Descriptor", "Corrupt GIF");

        g->line_size = g->w * 4;
        g->start_x = x * 4;
        g->start_y = y * g->line_size;
        g->max_x = g->start_x + w * 4;
        g->max_y = g->start_y + h * g->line_size;
        g->cur_x = g->start_x;
        g->cur_y = g->start_y;

        // if the width of the specified rectangle is 0, that means
        // we may not see *any* pixels or the image is malformed;
        // to make sure this is caught, move the current y down to
        // max_y (which is what out_gif_code checks).
        if (w == 0) g->cur_y = g->max_y;

        g->lflags = stbi__get8(s);

        if (g->lflags & 0x40) {
          g->step = 8 * g->line_size;  // first interlaced spacing
          g->parse = 3;
        } else {
          g->step = g->line_size;
          g->parse = 0;
        }

        if (g->lflags & 0x80) {
          stbi__gif_parse_colortable(s, g->lpal, 2 << (g->lflags & 7),
                                     g->eflags & 0x01 ? g->transparent : -1);
          g->color_table = (unsigned char *)g->lpal;
        } else if (g->flags & 0x80) {
          g->color_table = (unsigned char *)g->pal;
        } else
          return stbi__errpuc("missing color table", "Corrupt GIF");

        o = stbi__process_gif_raster(s, g);
        if (!o) return NULL;

        // if this was the first frame,
        pcount = g->w * g->h;
        if (first_frame && (g->bgindex > 0)) {
          // if first frame, any pixel not drawn to gets the background color
          for (pi = 0; pi < pcount; ++pi) {
            if (g->history[pi] == 0) {
              g->pal[g->bgindex][3] =
                  255;  // just in case it was made transparent, undo that; It
                        // will be reset next frame if need be;
              memcpy(&g->out[pi * 4], &g->pal[g->bgindex], 4);
            }
          }
        }

        return o;
      }

      case 0x21:  // Comment Extension.
      {
        int len;
        int ext = stbi__get8(s);
        if (ext == 0xF9) {  // Graphic Control Extension.
          len = stbi__get8(s);
          if (len == 4) {
            g->eflags = stbi__get8(s);
            g->delay =
                10 *
                stbi__get16le(
                    s);  // delay - 1/100th of a second, saving as 1/1000ths.

            // unset old transparent
            if (g->transparent >= 0) {
              g->pal[g->transparent][3] = 255;
            }
            if (g->eflags & 0x01) {
              g->transparent = stbi__get8(s);
              if (g->transparent >= 0) {
                g->pal[g->transparent][3] = 0;
              }
            } else {
              // don't need transparent
              stbi__skip(s, 1);
              g->transparent = -1;
            }
          } else {
            stbi__skip(s, len);
            break;
          }
        }
        while ((len = stbi__get8(s)) != 0) {
          stbi__skip(s, len);
        }
        break;
      }

      case 0x3B:  // gif stream termination code
        return (
            unsigned char *)s;  // using '1' causes warning on some compilers

      default:
        return stbi__errpuc("unknown code", "Corrupt GIF");
    }
  }
}

static void *stbi__load_gif_main(stbi__context *s, int **delays, int *x, int *y,
                                 int *z, int *comp, int req_comp) {
  if (stbi__gif_test(s)) {
    int layers = 0;
    unsigned char *u = 0;
    unsigned char *out = 0;
    unsigned char *two_back = 0;
    stbi__gif *g;
    int stride;
    g = calloc(1, sizeof(stbi__gif));
    if (delays) {
      *delays = 0;
    }
    do {
      u = stbi__gif_load_next(s, g, comp, req_comp, two_back);
      if (u == (unsigned char *)s) u = 0;  // end of animated gif marker
      if (u) {
        *x = g->w;
        *y = g->h;
        ++layers;
        stride = g->w * g->h * 4;
        if (out) {
          out = (unsigned char *)realloc(out, layers * stride);
          if (!out) abort();
          if (delays) {
            *delays = (int *)realloc(*delays, sizeof(int) * layers);
            if (!*delays) abort();
          }
        } else {
          out = malloc(layers * stride);
          if (delays) {
            *delays = malloc(layers * sizeof(int));
          }
        }
        memcpy(out + ((layers - 1) * stride), u, stride);
        if (layers >= 2) {
          two_back = out - 2 * stride;
        }
        if (delays) {
          (*delays)[layers - 1U] = g->delay;
        }
      }
    } while (u != 0);
    free(g->out);
    free(g->history);
    free(g->background);
    // do the final conversion after loading everything;
    if (req_comp && req_comp != 4)
      out = stbi__convert_format(out, 4, req_comp, layers * g->w, g->h);

    free(g);
    *z = layers;
    return out;
  } else {
    return stbi__errpuc("not GIF", "Image was not as a gif type.");
  }
}

static noinline void *stbi__gif_load(stbi__context *s, int *x, int *y,
                                     int *comp, int req_comp,
                                     stbi__result_info *ri) {
  unsigned char *u = 0;
  stbi__gif *g;
  g = calloc(1, sizeof(stbi__gif));
  u = stbi__gif_load_next(s, g, comp, req_comp, 0);
  if (u == (unsigned char *)s) u = 0;  // end of animated gif marker
  if (u) {
    *x = g->w;
    *y = g->h;
    // moved conversion to after successful load so that the same
    // can be done for multiple frames.
    if (req_comp && req_comp != 4)
      u = stbi__convert_format(u, 4, req_comp, g->w, g->h);
  } else if (g->out) {
    // if there was an error and we allocated an image buffer, free it!
    free(g->out);
  }
  // free buffers needed for multiple frame loading;
  free(g->history);
  free(g->background);
  free(g);
  return u;
}

static int stbi__gif_info(stbi__context *s, int *x, int *y, int *comp) {
  return stbi__gif_info_raw(s, x, y, comp);
}

// ********************************************************************
// Portable Gray Map and Portable Pixel Map loader
// by Ken Miller
//
// PGM: http://netpbm.sourceforge.net/doc/pgm.html
// PPM: http://netpbm.sourceforge.net/doc/ppm.html
//
// Known limitations:
//    Does not support comments in the header section
//    Does not support ASCII image data (formats P2 and P3)
//    Does not support 16-bit-per-channel

static int stbi__pnm_test(stbi__context *s) {
  char p, t;
  p = (char)stbi__get8(s);
  t = (char)stbi__get8(s);
  if (p != 'P' || (t != '5' && t != '6')) {
    stbi__rewind(s);
    return 0;
  }
  return 1;
}

static noinline void *stbi__pnm_load(stbi__context *s, int *x, int *y,
                                     int *comp, int req_comp,
                                     stbi__result_info *ri) {
  unsigned char *out;
  if (!stbi__pnm_info(s, (int *)&s->img_x, (int *)&s->img_y,
                      (int *)&s->img_n)) {
    return 0;
  }
  *x = s->img_x;
  *y = s->img_y;
  if (comp) *comp = s->img_n;
  if (!stbi__mad3sizes_valid(s->img_n, s->img_x, s->img_y, 0)) {
    return stbi__errpuc("too large", "PNM too large");
  }
  out = stbi__malloc_mad3(s->img_n, s->img_x, s->img_y, 0);
  stbi__getn(s, out, s->img_n * s->img_x * s->img_y);
  if (req_comp && req_comp != s->img_n) {
    out = stbi__convert_format(out, s->img_n, req_comp, s->img_x, s->img_y);
    if (out == NULL) return out;  // stbi__convert_format frees input on failure
  }
  return out;
}

static int stbi__pnm_isspace(char c) {
  return c == ' ' || c == '\t' || c == '\n' || c == '\v' || c == '\f' ||
         c == '\r';
}

static void stbi__pnm_skip_whitespace(stbi__context *s, char *c) {
  for (;;) {
    while (!stbi__at_eof(s) && stbi__pnm_isspace(*c)) *c = (char)stbi__get8(s);
    if (stbi__at_eof(s) || *c != '#') break;
    while (!stbi__at_eof(s) && *c != '\n' && *c != '\r')
      *c = (char)stbi__get8(s);
  }
}

static int stbi__pnm_isdigit(char c) {
  return c >= '0' && c <= '9';
}

static int stbi__pnm_getinteger(stbi__context *s, char *c) {
  int value = 0;
  while (!stbi__at_eof(s) && stbi__pnm_isdigit(*c)) {
    value = value * 10 + (*c - '0');
    *c = (char)stbi__get8(s);
  }
  return value;
}

static int stbi__pnm_info(stbi__context *s, int *x, int *y, int *comp) {
  int maxv, dummy;
  char c, p, t;
  if (!x) x = &dummy;
  if (!y) y = &dummy;
  if (!comp) comp = &dummy;
  stbi__rewind(s);
  // Get identifier
  p = (char)stbi__get8(s);
  t = (char)stbi__get8(s);
  if (p != 'P' || (t != '5' && t != '6')) {
    stbi__rewind(s);
    return 0;
  }
  *comp =
      (t == '6') ? 3 : 1;  // '5' is 1-component .pgm; '6' is 3-component .ppm
  c = (char)stbi__get8(s);
  stbi__pnm_skip_whitespace(s, &c);
  *x = stbi__pnm_getinteger(s, &c);  // read width
  stbi__pnm_skip_whitespace(s, &c);
  *y = stbi__pnm_getinteger(s, &c);  // read height
  stbi__pnm_skip_whitespace(s, &c);
  maxv = stbi__pnm_getinteger(s, &c);  // read max value
  if (maxv > 255)
    return stbi__err("max value > 255", "PPM image not 8-bit");
  else {
    return 1;
  }
}

static int stbi__info_main(stbi__context *s, int *x, int *y, int *comp) {
#ifndef STBI_NO_JPEG
  if (stbi__jpeg_info(s, x, y, comp)) return 1;
#endif
#ifndef STBI_NO_PNG
  if (stbi__png_info(s, x, y, comp)) return 1;
#endif
#ifndef STBI_NO_GIF
  if (stbi__gif_info(s, x, y, comp)) return 1;
#endif
#ifndef STBI_NO_PNM
  if (stbi__pnm_info(s, x, y, comp)) return 1;
#endif
  return stbi__err("unknown image type",
                   "Image not of any known type, or corrupt");
}

static int stbi__is_16_main(stbi__context *s) {
  if (stbi__png_is16(s)) return 1;
  return 0;
}

int stbi_info(char const *filename, int *x, int *y, int *comp) {
  FILE *f = stbi__fopen(filename, "rb");
  int result;
  if (!f) return stbi__err("can't fopen", "Unable to open file");
  result = stbi_info_from_file(f, x, y, comp);
  fclose(f);
  return result;
}

int stbi_info_from_file(FILE *f, int *x, int *y, int *comp) {
  int r;
  stbi__context s;
  long pos = ftell(f);
  stbi__start_file(&s, f);
  r = stbi__info_main(&s, x, y, comp);
  fseek(f, pos, SEEK_SET);
  return r;
}

int stbi_is_16_bit(char const *filename) {
  FILE *f = stbi__fopen(filename, "rb");
  int result;
  if (!f) return stbi__err("can't fopen", "Unable to open file");
  result = stbi_is_16_bit_from_file(f);
  fclose(f);
  return result;
}

int stbi_is_16_bit_from_file(FILE *f) {
  int r;
  stbi__context s;
  long pos = ftell(f);
  stbi__start_file(&s, f);
  r = stbi__is_16_main(&s);
  fseek(f, pos, SEEK_SET);
  return r;
}

int stbi_info_from_memory(unsigned char const *buffer, int len, int *x, int *y,
                          int *comp) {
  stbi__context s;
  stbi__start_mem(&s, buffer, len);
  return stbi__info_main(&s, x, y, comp);
}

int stbi_info_from_callbacks(stbi_io_callbacks const *c, void *user, int *x,
                             int *y, int *comp) {
  stbi__context s;
  stbi__start_callbacks(&s, (stbi_io_callbacks *)c, user);
  return stbi__info_main(&s, x, y, comp);
}

int stbi_is_16_bit_from_memory(unsigned char const *buffer, int len) {
  stbi__context s;
  stbi__start_mem(&s, buffer, len);
  return stbi__is_16_main(&s);
}

int stbi_is_16_bit_from_callbacks(stbi_io_callbacks const *c, void *user) {
  stbi__context s;
  stbi__start_callbacks(&s, (stbi_io_callbacks *)c, user);
  return stbi__is_16_main(&s);
}