lib/strtod.c

   1 /* Copyright (C) 1991, 1992 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <errno.h>
  20 #include <ctype.h>
  21 #include <math.h>
  22
  23 #if STDC_HEADERS
  24 #include <float.h>
  25 #include <stdlib.h>
  26 #include <string.h>
  27 #else
  28 #define NULL 0
  29 #define DBL_MAX 1.7976931348623159e+308
  30 #define DBL_MIN 2.2250738585072010e-308
  31 extern int errno;
  32 #endif
  33 #ifndef HUGE_VAL
  34 #define HUGE_VAL HUGE
  35 #endif
  36
  37 #if !__STDC__
  38 #define const
  39 #endif
  40
  41 /* Convert NPTR to a double.  If ENDPTR is not NULL, a pointer to the
  42    character after the last one used in the number is put in *ENDPTR.  */
  43 double
  44 strtod (nptr, endptr)
  45      const char *nptr;
  46      char **endptr;
  47 {
  48   register const char *s;
  49   short int sign;
  50
  51   /* The number so far.  */
  52   double num;
  53
  54   int got_dot;                  /* Found a decimal point.  */
  55   int got_digit;                /* Seen any digits.  */
  56
  57   /* The exponent of the number.  */
  58   long int exponent;
  59
  60   if (nptr == NULL)
  61     {
  62       errno = EINVAL;
  63       goto noconv;
  64     }
  65
  66   s = nptr;
  67
  68   /* Eat whitespace.  */
  69   while (isspace (*s))
  70     ++s;
  71
  72   /* Get the sign.  */
  73   sign = *s == '-' ? -1 : 1;
  74   if (*s == '-' || *s == '+')
  75     ++s;
  76
  77   num = 0.0;
  78   got_dot = 0;
  79   got_digit = 0;
  80   exponent = 0;
  81   for (;; ++s)
  82     {
  83       if (isdigit (*s))
  84         {
  85           got_digit = 1;
  86
  87           /* Make sure that multiplication by 10 will not overflow.  */
  88           if (num > DBL_MAX * 0.1)
  89             /* The value of the digit doesn't matter, since we have already
  90                gotten as many digits as can be represented in a `double'.
  91                This doesn't necessarily mean the result will overflow.
  92                The exponent may reduce it to within range.
  93
  94                We just need to record that there was another
  95                digit so that we can multiply by 10 later.  */
  96             ++exponent;
  97           else
  98             num = (num * 10.0) + (*s - '0');
  99
 100           /* Keep track of the number of digits after the decimal point.
 101              If we just divided by 10 here, we would lose precision.  */
 102           if (got_dot)
 103             --exponent;
 104         }
 105       else if (!got_dot && *s == '.')
 106         /* Record that we have found the decimal point.  */
 107         got_dot = 1;
 108       else
 109         /* Any other character terminates the number.  */
 110         break;
 111     }
 112
 113   if (!got_digit)
 114     goto noconv;
 115
 116   if (tolower (*s) == 'e')
 117     {
 118       /* Get the exponent specified after the `e' or `E'.  */
 119       int save = errno;
 120       char *end;
 121       long int exp;
 122
 123       errno = 0;
 124       ++s;
 125       exp = strtol (s, &end, 10);
 126       if (errno == ERANGE)
 127         {
 128           /* The exponent overflowed a `long int'.  It is probably a safe
 129              assumption that an exponent that cannot be represented by
 130              a `long int' exceeds the limits of a `double'.  */
 131           if (endptr != NULL)
 132             *endptr = end;
 133           if (exp < 0)
 134             goto underflow;
 135           else
 136             goto overflow;
 137         }
 138       else if (end == s)
 139         /* There was no exponent.  Reset END to point to
 140            the 'e' or 'E', so *ENDPTR will be set there.  */
 141         end = (char *) s - 1;
 142       errno = save;
 143       s = end;
 144       exponent += exp;
 145     }
 146
 147   if (endptr != NULL)
 148     *endptr = (char *) s;
 149
 150   if (num == 0.0)
 151     return 0.0;
 152
 153   /* Multiply NUM by 10 to the EXPONENT power,
 154      checking for overflow and underflow.  */
 155
 156   if (exponent < 0)
 157     {
 158       if (num < DBL_MIN * pow (10.0, (double) -exponent))
 159         goto underflow;
 160     }
 161   else if (exponent > 0)
 162     {
 163       if (num > DBL_MAX * pow (10.0, (double) -exponent))
 164         goto overflow;
 165     }
 166
 167   num *= pow (10.0, (double) exponent);
 168
 169   return num * sign;
 170
 171 overflow:
 172   /* Return an overflow error.  */
 173   errno = ERANGE;
 174   return HUGE_VAL * sign;
 175
 176 underflow:
 177   /* Return an underflow error.  */
 178   if (endptr != NULL)
 179     *endptr = (char *) nptr;
 180   errno = ERANGE;
 181   return 0.0;
 182
 183 noconv:
 184   /* There was no number.  */
 185   if (endptr != NULL)
 186     *endptr = (char *) nptr;
 187   return 0.0;
 188 }