cosmopolitan/libc/intrin/formathex64.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et 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/fmt/itoa.h"
#include "libc/intrin/bsr.h"
#include "libc/macros.h"

static inline int PickGoodWidth(unsigned x, char z) {
  if (z) {
    if (x < 16) {
      if (x < 8)
        return 8;
      return 16;
    } else {
      if (x < 32)
        return 32;
      return 64;
    }
  } else {
    return ROUNDUP(x + 1, 4);
  }
}

/**
 * Converts unsigned 64-bit integer to hex string.
 *
 * @param p needs at least 19 bytes
 * @param z is 0 for DIGITS, 1 for 0xDIGITS, 2 for 0xDIGITS if ≠0
 * @return pointer to nul byte
 */
char *FormatHex64(char p[hasatleast 19], uint64_t x, char z) {
  int i;
  if (x) {
    if (z) {
      *p++ = '0';
      *p++ = 'x';
    }
    i = PickGoodWidth(bsrl(x), z);
    do {
      *p++ = "0123456789abcdef"[(x >> (i -= 4)) & 15];
    } while (i);
  } else {
    if (z == 1) {
      *p++ = '0';
      *p++ = 'x';
    }
    *p++ = '0';
  }
  *p = 0;
  return p;
}