com32/lib/math/strtod.c

   1 /*
   2  * strtod.c
   3  *
   4  * Convert string to double
   5  *
   6  * Copyright (C) 2002 Michael Ringgaard. All rights reserved.
   7  * Copyright 2006-2008 H. Peter Anvin - All Rights Reserved
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  *
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the project nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  23  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  24  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  25  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  26  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  27  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  28  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  29  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  31  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  32  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  33  * OF THE POSSIBILITY OF SUCH DAMAGE.
  34  */
  35
  36 #include <errno.h>
  37 #include <ctype.h>
  38 #include <stdlib.h>
  39 #include <math.h>
  40
  41 static inline int is_real(double x)
  42 {
  43   const double Inf = 1.0/0.0;
  44   return (x < Inf) && (x >= -Inf);
  45 }
  46
  47 double strtod(const char *str, char **endptr)
  48 {
  49   double number;
  50   int exponent;
  51   int negative;
  52   char *p = (char *) str;
  53   double p10;
  54   int n;
  55   int num_digits;
  56   int num_decimals;
  57   const double Inf = 1.0/0.0;
  58
  59   // Skip leading whitespace
  60   while (isspace(*p)) p++;
  61
  62   // Handle optional sign
  63   negative = 0;
  64   switch (*p)
  65   {
  66     case '-': negative = 1; // Fall through to increment position
  67     case '+': p++;
  68   }
  69
  70   number = 0.;
  71   exponent = 0;
  72   num_digits = 0;
  73   num_decimals = 0;
  74
  75   // Process string of digits
  76   while (isdigit(*p))
  77   {
  78     number = number * 10. + (*p - '0');
  79     p++;
  80     num_digits++;
  81   }
  82
  83   // Process decimal part
  84   if (*p == '.')
  85   {
  86     p++;
  87
  88     while (isdigit(*p))
  89     {
  90       number = number * 10. + (*p - '0');
  91       p++;
  92       num_digits++;
  93       num_decimals++;
  94     }
  95
  96     exponent -= num_decimals;
  97   }
  98
  99   if (num_digits == 0)
 100   {
 101     errno = ERANGE;
 102     return 0.0;
 103   }
 104
 105   // Correct for sign
 106   if (negative) number = -number;
 107
 108   // Process an exponent string
 109   if (*p == 'e' || *p == 'E')
 110   {
 111     // Handle optional sign
 112     negative = 0;
 113     switch(*++p)
 114     {
 115       case '-': negative = 1;   // Fall through to increment pos
 116       case '+': p++;
 117     }
 118
 119     // Process string of digits
 120     n = 0;
 121     while (isdigit(*p))
 122     {
 123       n = n * 10 + (*p - '0');
 124       p++;
 125     }
 126
 127     if (negative)
 128       exponent -= n;
 129     else
 130       exponent += n;
 131   }
 132
 133   if (exponent < __DBL_MIN_EXP__  ||
 134       exponent > __DBL_MAX_EXP__)
 135   {
 136     errno = ERANGE;
 137     return Inf;
 138   }
 139
 140   // Scale the result
 141   p10 = 10.;
 142   n = exponent;
 143   if (n < 0) n = -n;
 144   while (n)
 145   {
 146     if (n & 1)
 147     {
 148       if (exponent < 0)
 149         number /= p10;
 150       else
 151         number *= p10;
 152     }
 153     n >>= 1;
 154     p10 *= p10;
 155   }
 156
 157   if (!is_real(number)) errno = ERANGE;
 158   if (endptr) *endptr = p;
 159
 160   return number;
 161 }