libc-bottom-half/cloudlibc/src/common/parser_strtoint.h

   1 // Copyright (c) 2015 Nuxi, https://nuxi.nl/
   2 //
   3 // SPDX-License-Identifier: BSD-2-Clause
   4
   5 // Parser of integer literals as performed by strtol(), scanf(), etc.
   6
   7 // Result of parsing.
   8 bool have_number = false;
   9 bool have_overflow = false;
  10 int_t number = 0;
  11
  12 {
  13   // Negative or positive number?
  14   bool negative = false;
  15   if (allow_negative && PEEK(0) == '-') {
  16     negative = true;
  17     SKIP(1);
  18   } else if (PEEK(0) == '+') {
  19     SKIP(1);
  20   }
  21
  22   // Determine the base.
  23   if ((base == 0 || base == 16) && PEEK(0) == '0' &&
  24       (PEEK(1) == 'x' || PEEK(1) == 'X') &&
  25       ((PEEK(2) >= '0' && PEEK(2) <= '9') ||
  26        (PEEK(2) >= 'A' && PEEK(2) <= 'F') ||
  27        (PEEK(2) >= 'a' && PEEK(2) <= 'f'))) {
  28     SKIP(2);
  29     base = 16;
  30   } else if (base == 0) {
  31     base = PEEK(0) == '0' ? 8 : 10;
  32   }
  33
  34   // Only perform conversion if the base is valid.
  35   if (base >= 2 && base <= 36) {
  36     uint_fast8_t radix = base;
  37
  38     // Determine the highest value up to which we can parse so that the
  39     // next digit does not cause an overflow.
  40     uintmax_t ceil;
  41     uint_fast8_t last_digit;
  42     if (negative) {
  43       ceil = -(min / radix);
  44       last_digit = -(min % radix);
  45     } else {
  46       ceil = max / radix;
  47       last_digit = max % radix;
  48     }
  49
  50     uintmax_t value = 0;
  51     for (;;) {
  52       // Parse next digit.
  53       uint_fast8_t digit;
  54       if (PEEK(0) >= '0' && PEEK(0) <= '9')
  55         digit = PEEK(0) - '0';
  56       else if (PEEK(0) >= 'A' && PEEK(0) <= 'Z')
  57         digit = PEEK(0) - 'A' + 10;
  58       else if (PEEK(0) >= 'a' && PEEK(0) <= 'z')
  59         digit = PEEK(0) - 'a' + 10;
  60       else
  61         break;
  62       if (digit >= radix)
  63         break;
  64       SKIP(1);
  65
  66       // Add it to result.
  67       have_number = true;
  68       if (value > ceil || (value == ceil && digit > last_digit)) {
  69         // Addition of the new digit would cause an overflow.
  70         have_overflow = true;
  71       } else {
  72         value = value * radix + digit;
  73       }
  74     }
  75
  76     if (have_overflow) {
  77       // Set value to min or max depending whether the input is negative
  78       // and whether the output type is signed.
  79       number = (int_t)-1 >= 0 || !negative ? max : min;
  80     } else {
  81       // Return parsed value.
  82       number = negative ? -value : value;
  83     }
  84   }
  85 }