lib/strtod.c

   1 /* Copyright (C) 1991, 1992, 1997, 1999 Free Software Foundation, Inc.
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; either version 2, or (at your option)
   6    any later version.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program; if not, write to the Free Software Foundation,
  15    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  16
  17 #if HAVE_CONFIG_H
  18 # include <config.h>
  19 #endif
  20
  21 #include <errno.h>
  22 #ifndef errno
  23 extern int errno;
  24 #endif
  25
  26 #include <ctype.h>
  27
  28 #if defined (STDC_HEADERS) || (!defined (isascii) && !defined (HAVE_ISASCII))
  29 # define IN_CTYPE_DOMAIN(c) 1
  30 #else
  31 # define IN_CTYPE_DOMAIN(c) isascii(c)
  32 #endif
  33
  34 #define ISSPACE(c) (IN_CTYPE_DOMAIN (c) && isspace (c))
  35 #define ISDIGIT(c) (IN_CTYPE_DOMAIN (c) && isdigit (c))
  36 #define TOLOWER(c) (IN_CTYPE_DOMAIN (c) ? tolower(c) : (c))
  37
  38 #include <math.h>
  39
  40 #if HAVE_FLOAT_H
  41 # include <float.h>
  42 #else
  43 # define DBL_MAX 1.7976931348623159e+308
  44 # define DBL_MIN 2.2250738585072010e-308
  45 #endif
  46
  47 #if STDC_HEADERS
  48 # include <stdlib.h>
  49 # include <string.h>
  50 #else
  51 # define NULL 0
  52 # ifndef HUGE_VAL
  53 #  define HUGE_VAL HUGE
  54 # endif
  55 #endif
  56
  57 /* Convert NPTR to a double.  If ENDPTR is not NULL, a pointer to the
  58    character after the last one used in the number is put in *ENDPTR.  */
  59 double
  60 strtod (const char *nptr, char **endptr)
  61 {
  62   register const char *s;
  63   short int sign;
  64
  65   /* The number so far.  */
  66   double num;
  67
  68   int got_dot;                  /* Found a decimal point.  */
  69   int got_digit;                /* Seen any digits.  */
  70
  71   /* The exponent of the number.  */
  72   long int exponent;
  73
  74   if (nptr == NULL)
  75     {
  76       errno = EINVAL;
  77       goto noconv;
  78     }
  79
  80   s = nptr;
  81
  82   /* Eat whitespace.  */
  83   while (ISSPACE (*s))
  84     ++s;
  85
  86   /* Get the sign.  */
  87   sign = *s == '-' ? -1 : 1;
  88   if (*s == '-' || *s == '+')
  89     ++s;
  90
  91   num = 0.0;
  92   got_dot = 0;
  93   got_digit = 0;
  94   exponent = 0;
  95   for (;; ++s)
  96     {
  97       if (ISDIGIT (*s))
  98         {
  99           got_digit = 1;
 100
 101           /* Make sure that multiplication by 10 will not overflow.  */
 102           if (num > DBL_MAX * 0.1)
 103             /* The value of the digit doesn't matter, since we have already
 104                gotten as many digits as can be represented in a `double'.
 105                This doesn't necessarily mean the result will overflow.
 106                The exponent may reduce it to within range.
 107
 108                We just need to record that there was another
 109                digit so that we can multiply by 10 later.  */
 110             ++exponent;
 111           else
 112             num = (num * 10.0) + (*s - '0');
 113
 114           /* Keep track of the number of digits after the decimal point.
 115              If we just divided by 10 here, we would lose precision.  */
 116           if (got_dot)
 117             --exponent;
 118         }
 119       else if (!got_dot && *s == '.')
 120         /* Record that we have found the decimal point.  */
 121         got_dot = 1;
 122       else
 123         /* Any other character terminates the number.  */
 124         break;
 125     }
 126
 127   if (!got_digit)
 128     goto noconv;
 129
 130   if (TOLOWER (*s) == 'e')
 131     {
 132       /* Get the exponent specified after the `e' or `E'.  */
 133       int save = errno;
 134       char *end;
 135       long int exp;
 136
 137       errno = 0;
 138       ++s;
 139       exp = strtol (s, &end, 10);
 140       if (errno == ERANGE)
 141         {
 142           /* The exponent overflowed a `long int'.  It is probably a safe
 143              assumption that an exponent that cannot be represented by
 144              a `long int' exceeds the limits of a `double'.  */
 145           if (endptr != NULL)
 146             *endptr = end;
 147           if (exp < 0)
 148             goto underflow;
 149           else
 150             goto overflow;
 151         }
 152       else if (end == s)
 153         /* There was no exponent.  Reset END to point to
 154            the 'e' or 'E', so *ENDPTR will be set there.  */
 155         end = (char *) s - 1;
 156       errno = save;
 157       s = end;
 158       exponent += exp;
 159     }
 160
 161   if (endptr != NULL)
 162     *endptr = (char *) s;
 163
 164   if (num == 0.0)
 165     return 0.0;
 166
 167   /* Multiply NUM by 10 to the EXPONENT power,
 168      checking for overflow and underflow.  */
 169
 170   if (exponent < 0)
 171     {
 172       if (num < DBL_MIN * pow (10.0, (double) -exponent))
 173         goto underflow;
 174     }
 175   else if (exponent > 0)
 176     {
 177       if (num > DBL_MAX * pow (10.0, (double) -exponent))
 178         goto overflow;
 179     }
 180
 181   num *= pow (10.0, (double) exponent);
 182
 183   return num * sign;
 184
 185 overflow:
 186   /* Return an overflow error.  */
 187   errno = ERANGE;
 188   return HUGE_VAL * sign;
 189
 190 underflow:
 191   /* Return an underflow error.  */
 192   if (endptr != NULL)
 193     *endptr = (char *) nptr;
 194   errno = ERANGE;
 195   return 0.0;
 196
 197 noconv:
 198   /* There was no number.  */
 199   if (endptr != NULL)
 200     *endptr = (char *) nptr;
 201   return 0.0;
 202 }