lib/strtod.c

   1 /* Copyright (C) 1991, 1992 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
  15    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  16
  17 #ifdef 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 #include <math.h>
  28
  29 #ifdef HAVE_FLOAT_H
  30 #include <float.h>
  31 #else
  32 #define DBL_MAX 1.7976931348623159e+308
  33 #define DBL_MIN 2.2250738585072010e-308
  34 #endif
  35
  36 #if STDC_HEADERS
  37 #include <stdlib.h>
  38 #include <string.h>
  39 #else
  40 #define NULL 0
  41 #ifndef HUGE_VAL
  42 #define HUGE_VAL HUGE
  43 #endif
  44 #endif
  45
  46 /* Convert NPTR to a double.  If ENDPTR is not NULL, a pointer to the
  47    character after the last one used in the number is put in *ENDPTR.  */
  48 double
  49 strtod (nptr, endptr)
  50      const char *nptr;
  51      char **endptr;
  52 {
  53   register const char *s;
  54   short int sign;
  55
  56   /* The number so far.  */
  57   double num;
  58
  59   int got_dot;                  /* Found a decimal point.  */
  60   int got_digit;                /* Seen any digits.  */
  61
  62   /* The exponent of the number.  */
  63   long int exponent;
  64
  65   if (nptr == NULL)
  66     {
  67       errno = EINVAL;
  68       goto noconv;
  69     }
  70
  71   s = nptr;
  72
  73   /* Eat whitespace.  */
  74   while (isspace (*s))
  75     ++s;
  76
  77   /* Get the sign.  */
  78   sign = *s == '-' ? -1 : 1;
  79   if (*s == '-' || *s == '+')
  80     ++s;
  81
  82   num = 0.0;
  83   got_dot = 0;
  84   got_digit = 0;
  85   exponent = 0;
  86   for (;; ++s)
  87     {
  88       if (isdigit (*s))
  89         {
  90           got_digit = 1;
  91
  92           /* Make sure that multiplication by 10 will not overflow.  */
  93           if (num > DBL_MAX * 0.1)
  94             /* The value of the digit doesn't matter, since we have already
  95                gotten as many digits as can be represented in a `double'.
  96                This doesn't necessarily mean the result will overflow.
  97                The exponent may reduce it to within range.
  98
  99                We just need to record that there was another
 100                digit so that we can multiply by 10 later.  */
 101             ++exponent;
 102           else
 103             num = (num * 10.0) + (*s - '0');
 104
 105           /* Keep track of the number of digits after the decimal point.
 106              If we just divided by 10 here, we would lose precision.  */
 107           if (got_dot)
 108             --exponent;
 109         }
 110       else if (!got_dot && *s == '.')
 111         /* Record that we have found the decimal point.  */
 112         got_dot = 1;
 113       else
 114         /* Any other character terminates the number.  */
 115         break;
 116     }
 117
 118   if (!got_digit)
 119     goto noconv;
 120
 121   if (tolower (*s) == 'e')
 122     {
 123       /* Get the exponent specified after the `e' or `E'.  */
 124       int save = errno;
 125       char *end;
 126       long int exp;
 127
 128       errno = 0;
 129       ++s;
 130       exp = strtol (s, &end, 10);
 131       if (errno == ERANGE)
 132         {
 133           /* The exponent overflowed a `long int'.  It is probably a safe
 134              assumption that an exponent that cannot be represented by
 135              a `long int' exceeds the limits of a `double'.  */
 136           if (endptr != NULL)
 137             *endptr = end;
 138           if (exp < 0)
 139             goto underflow;
 140           else
 141             goto overflow;
 142         }
 143       else if (end == s)
 144         /* There was no exponent.  Reset END to point to
 145            the 'e' or 'E', so *ENDPTR will be set there.  */
 146         end = (char *) s - 1;
 147       errno = save;
 148       s = end;
 149       exponent += exp;
 150     }
 151
 152   if (endptr != NULL)
 153     *endptr = (char *) s;
 154
 155   if (num == 0.0)
 156     return 0.0;
 157
 158   /* Multiply NUM by 10 to the EXPONENT power,
 159      checking for overflow and underflow.  */
 160
 161   if (exponent < 0)
 162     {
 163       if (num < DBL_MIN * pow (10.0, (double) -exponent))
 164         goto underflow;
 165     }
 166   else if (exponent > 0)
 167     {
 168       if (num > DBL_MAX * pow (10.0, (double) -exponent))
 169         goto overflow;
 170     }
 171
 172   num *= pow (10.0, (double) exponent);
 173
 174   return num * sign;
 175
 176 overflow:
 177   /* Return an overflow error.  */
 178   errno = ERANGE;
 179   return HUGE_VAL * sign;
 180
 181 underflow:
 182   /* Return an underflow error.  */
 183   if (endptr != NULL)
 184     *endptr = (char *) nptr;
 185   errno = ERANGE;
 186   return 0.0;
 187
 188 noconv:
 189   /* There was no number.  */
 190   if (endptr != NULL)
 191     *endptr = (char *) nptr;
 192   return 0.0;
 193 }