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 (C) 2006 H. Peter Anvin.
   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 "AS IS" AND
  23 // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25 // ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
  26 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28 // OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29 // HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30 // LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31 // OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32 // SUCH DAMAGE.
  33 //
  34
  35 #include <errno.h>
  36 #include <ctype.h>
  37 #include <stdlib.h>
  38
  39 static inline int is_real(double x)
  40 {
  41   const double Inf = 1.0/0.0;
  42   return (x < Inf) && (x >= -Inf);
  43 }
  44
  45 double strtod(const char *str, char **endptr)
  46 {
  47   double number;
  48   int exponent;
  49   int negative;
  50   char *p = (char *) str;
  51   double p10;
  52   int n;
  53   int num_digits;
  54   int num_decimals;
  55   const double Inf = 1.0/0.0;
  56
  57   // Skip leading whitespace
  58   while (isspace(*p)) p++;
  59
  60   // Handle optional sign
  61   negative = 0;
  62   switch (*p)
  63   {
  64     case '-': negative = 1; // Fall through to increment position
  65     case '+': p++;
  66   }
  67
  68   number = 0.;
  69   exponent = 0;
  70   num_digits = 0;
  71   num_decimals = 0;
  72
  73   // Process string of digits
  74   while (isdigit(*p))
  75   {
  76     number = number * 10. + (*p - '0');
  77     p++;
  78     num_digits++;
  79   }
  80
  81   // Process decimal part
  82   if (*p == '.')
  83   {
  84     p++;
  85
  86     while (isdigit(*p))
  87     {
  88       number = number * 10. + (*p - '0');
  89       p++;
  90       num_digits++;
  91       num_decimals++;
  92     }
  93
  94     exponent -= num_decimals;
  95   }
  96
  97   if (num_digits == 0)
  98   {
  99     errno = ERANGE;
 100     return 0.0;
 101   }
 102
 103   // Correct for sign
 104   if (negative) number = -number;
 105
 106   // Process an exponent string
 107   if (*p == 'e' || *p == 'E')
 108   {
 109     // Handle optional sign
 110     negative = 0;
 111     switch(*++p)
 112     {
 113       case '-': negative = 1;   // Fall through to increment pos
 114       case '+': p++;
 115     }
 116
 117     // Process string of digits
 118     n = 0;
 119     while (isdigit(*p))
 120     {
 121       n = n * 10 + (*p - '0');
 122       p++;
 123     }
 124
 125     if (negative)
 126       exponent -= n;
 127     else
 128       exponent += n;
 129   }
 130
 131   if (exponent < __DBL_MIN_EXP__  ||
 132       exponent > __DBL_MAX_EXP__)
 133   {
 134     errno = ERANGE;
 135     return Inf;
 136   }
 137
 138   // Scale the result
 139   p10 = 10.;
 140   n = exponent;
 141   if (n < 0) n = -n;
 142   while (n)
 143   {
 144     if (n & 1)
 145     {
 146       if (exponent < 0)
 147         number /= p10;
 148       else
 149         number *= p10;
 150     }
 151     n >>= 1;
 152     p10 *= p10;
 153   }
 154
 155   if (!is_real(number)) errno = ERANGE;
 156   if (endptr) *endptr = p;
 157
 158   return number;
 159 }
 160