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  1. /* Copyright (C) 1994 DJ Delorie, see COPYING.DJ for details */
  2. #include <limits.h>
  3. #include <ctype.h>
  4. #include <errno.h>
  5. #include <stdlib.h>
  6. #include <libc/unconst.h>
  7.  
  8. long
  9. strtol(const char *nptr, char **endptr, int base)
  10. {
  11.   const char *s = nptr;
  12.   unsigned long acc;
  13.   int c;
  14.   unsigned long cutoff;
  15.   int neg = 0, any, cutlim;
  16.  
  17.   /*
  18.    * Skip white space and pick up leading +/- sign if any.
  19.    * If base is 0, allow 0x for hex and 0 for octal, else
  20.    * assume decimal; if base is already 16, allow 0x.
  21.    */
  22.   do {
  23.     c = *s++;
  24.   } while (isspace(c));
  25.   if (c == '-')
  26.   {
  27.     neg = 1;
  28.     c = *s++;
  29.   }
  30.   else if (c == '+')
  31.     c = *s++;
  32.   if ((base == 0 || base == 16) &&
  33.       c == '0' && (*s == 'x' || *s == 'X'))
  34.   {
  35.     c = s[1];
  36.     s += 2;
  37.     base = 16;
  38.   }
  39.   if (base == 0)
  40.     base = c == '0' ? 8 : 10;
  41.  
  42.   /*
  43.    * Compute the cutoff value between legal numbers and illegal
  44.    * numbers.  That is the largest legal value, divided by the
  45.    * base.  An input number that is greater than this value, if
  46.    * followed by a legal input character, is too big.  One that
  47.    * is equal to this value may be valid or not; the limit
  48.    * between valid and invalid numbers is then based on the last
  49.    * digit.  For instance, if the range for longs is
  50.    * [-2147483648..2147483647] and the input base is 10,
  51.    * cutoff will be set to 214748364 and cutlim to either
  52.    * 7 (neg==0) or 8 (neg==1), meaning that if we have accumulated
  53.    * a value > 214748364, or equal but the next digit is > 7 (or 8),
  54.    * the number is too big, and we will return a range error.
  55.    *
  56.    * Set any if any `digits' consumed; make it negative to indicate
  57.    * overflow.
  58.    */
  59.   cutoff = neg ? -(unsigned long)LONG_MIN : LONG_MAX;
  60.   cutlim = cutoff % (unsigned long)base;
  61.   cutoff /= (unsigned long)base;
  62.   for (acc = 0, any = 0;; c = *s++)
  63.   {
  64.     if (isdigit(c))
  65.       c -= '0';
  66.     else if (isalpha(c))
  67.       c -= isupper(c) ? 'A' - 10 : 'a' - 10;
  68.     else
  69.       break;
  70.     if (c >= base)
  71.       break;
  72.     if (any < 0 || acc > cutoff || (acc == cutoff && c > cutlim))
  73.       any = -1;
  74.     else
  75.     {
  76.       any = 1;
  77.       acc *= base;
  78.       acc += c;
  79.     }
  80.   }
  81.   if (any < 0)
  82.   {
  83.     acc = neg ? LONG_MIN : LONG_MAX;
  84.     errno = ERANGE;
  85.   }
  86.   else if (neg)
  87.     acc = -acc;
  88.   if (endptr != 0)
  89.     *endptr = any ? unconst(s, char *) - 1 : unconst(nptr, char *);
  90.   return acc;
  91. }
  92.