strtol.c

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#include <precomp.h>

/*
 * @implemented
 */
long
strtol(const char *nptr, char **endptr, int base)
{
  const char *s = nptr;
  unsigned long acc;
  int c;
  unsigned long cutoff;
  int neg = 0, any, cutlim;

  /*
   * Skip white space and pick up leading +/- sign if any.
   * If base is 0, allow 0x for hex and 0 for octal, else
   * assume decimal; if base is already 16, allow 0x.
   */
  do {
    c = *s++;
  } while (isspace(c));
  if (c == '-')
  {
    neg = 1;
    c = *s++;
  }
  else if (c == '+')
    c = *s++;
  if ((base == 0 || base == 16) &&
      c == '0' && (*s == 'x' || *s == 'X'))
  {
    c = s[1];
    s += 2;
    base = 16;
  }
  if (base == 0)
    base = c == '0' ? 8 : 10;

  /*
   * Compute the cutoff value between legal numbers and illegal
   * numbers.  That is the largest legal value, divided by the
   * base.  An input number that is greater than this value, if
   * followed by a legal input character, is too big.  One that
   * is equal to this value may be valid or not; the limit
   * between valid and invalid numbers is then based on the last
   * digit.  For instance, if the range for longs is
   * [-2147483648..2147483647] and the input base is 10,
   * cutoff will be set to 214748364 and cutlim to either
   * 7 (neg==0) or 8 (neg==1), meaning that if we have accumulated
   * a value > 214748364, or equal but the next digit is > 7 (or 8),
   * the number is too big, and we will return a range error.
   *
   * Set any if any `digits' consumed; make it negative to indicate
   * overflow.
   */
  cutoff = neg ? ((unsigned long)LONG_MAX+1) : LONG_MAX;
  cutlim = cutoff % (unsigned long)base;
  cutoff /= (unsigned long)base;
  for (acc = 0, any = 0;; c = *s++)
  {
    if (isdigit(c))
      c -= '0';
    else if (isalpha(c))
      c -= isupper(c) ? 'A' - 10 : 'a' - 10;
    else
      break;
    if (c >= base)
      break;
    if (any < 0 || acc > cutoff || (acc == cutoff && c > cutlim))
      any = -1;
    else
    {
      any = 1;
      acc *= base;
      acc += c;
    }
  }
  if (any < 0)
  {
    acc = neg ? LONG_MIN : LONG_MAX;
#ifndef _LIBCNT_
    _set_errno(ERANGE);
#endif
  }
  else if (neg)
    acc = 0-acc;
  if (endptr != 0)
    *endptr = any ? (char *)((size_t)(s - 1)) : (char *)((size_t)nptr);
  return acc;
}