/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-â
âvi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :viâ
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â Copyright 2022 Justine Alexandra Roberts Tunney                              â
â                                                                              â
â Permission to use, copy, modify, and/or distribute this software for         â
â any purpose with or without fee is hereby granted, provided that the         â
â above copyright notice and this permission notice appear in all copies.      â
â                                                                              â
â THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                â
â WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                â
â WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             â
â AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         â
â DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        â
â PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               â
â TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             â
â PERFORMANCE OF THIS SOFTWARE.                                                â
ââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ*/
#include "libc/assert.h"
#include "libc/dce.h"
#include "libc/intrin/asan.internal.h"
#include "libc/str/str.h"

static noasan size_t strnlen_s_x64(const char *s, size_t n, size_t i) {
  uint64_t w;
  for (; i + 8 < n; i += 8) {
    w = *(uint64_t *)(s + i);
    if ((w = ~w & (w - 0x0101010101010101) & 0x8080808080808080)) {
      i += (unsigned)__builtin_ctzll(w) >> 3;
      break;
    }
  }
  return i;
}

/**
 * Returns length of NUL-terminated string... securely.
 *
 * This is like strnlen() except it'll return 0 if `s` is null. We also
 * make the assumption for the purposes of ASAN that `n` is the size of
 * the buffer if `s` is non-null.
 *
 * @param s is string
 * @param n is max length
 * @return byte length
 * @asyncsignalsafe
 */
noasan size_t strnlen_s(const char *s, size_t n) {
  size_t i;
  if (!s) return 0;
  if (IsAsan()) __asan_verify(s, n);
  for (i = 0; (uintptr_t)(s + i) & 7; ++i) {
    if (i == n || !s[i]) return i;
  }
  i = strnlen_s_x64(s, n, i);
  for (;; ++i) {
    if (i == n || !s[i]) break;
  }
  _unassert(i == n || (i < n && !s[i]));
  return i;
}
