/*-*- 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 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/ctype.h"
#include "libc/fmt/conv.h"
#include "libc/str/str.h"

/**
 * Turns string into int.
 *
 * Decimal is the only radix supported. Leading whitespace (as specified
 * by the isspace() function) is skipped over. Unlike strtol(), the atoi
 * function has undefined behavior on error and it never changes `errno`
 *
 * @param nptr is a non-null nul-terminated string
 * @return the decoded signed saturated integer
 */
int atoi(const char *nptr) {
  int x, c, d;
  do
    c = *nptr++;
  while (isspace(c));
  d = c == '-' ? -1 : 1;
  if (c == '-' || c == '+')
    c = *nptr++;
  for (x = 0; isdigit(c); c = *nptr++) {
    x *= 10;
    x += (c - '0') * d;
  }
  return x;
}
