/*-*- 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 2021 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/str/str.h"

static noasan inline const char *strchr_x64(const char *p, uint64_t c) {
  unsigned a, b;
  uint64_t w, x, y;
  for (c *= 0x0101010101010101;; p += 8) {
    w = (uint64_t)(255 & p[7]) << 070 | (uint64_t)(255 & p[6]) << 060 |
        (uint64_t)(255 & p[5]) << 050 | (uint64_t)(255 & p[4]) << 040 |
        (uint64_t)(255 & p[3]) << 030 | (uint64_t)(255 & p[2]) << 020 |
        (uint64_t)(255 & p[1]) << 010 | (uint64_t)(255 & p[0]) << 000;
    if ((x = ~(w ^ c) & ((w ^ c) - 0x0101010101010101) & 0x8080808080808080) |
        (y = ~w & (w - 0x0101010101010101) & 0x8080808080808080)) {
      if (x) {
        a = __builtin_ctzll(x);
        if (y) {
          b = __builtin_ctzll(y);
          if (a <= b) {
            return p + (a >> 3);
          } else {
            return NULL;
          }
        } else {
          return p + (a >> 3);
        }
      } else {
        return NULL;
      }
    }
  }
}

/**
 * Returns pointer to first instance of character.
 *
 * @param s is a NUL-terminated string
 * @param c is masked with 255 as byte to search for
 * @return pointer to first instance of c or NULL if not found
 *     noting that if c is NUL we return pointer to terminator
 * @asyncsignalsafe
 */
char *strchr(const char *s, int c) {
  char *r;
  for (c &= 255; (uintptr_t)s & 7; ++s) {
    if ((*s & 255) == c) return s;
    if (!*s) return NULL;
  }
  r = strchr_x64(s, c);
  assert(!r || *r || !c);
  return r;
}