Python/strtod.c

   1 #include <stdio.h>
   2 #include <string.h>
   3
   4 #include "pyconfig.h"
   5
   6 /* comp.sources.misc strtod(), as posted in comp.lang.tcl,
   7    with bugfix for "123000.0" and acceptance of space after 'e' sign nuked.
   8
   9    ************************************************************
  10    * YOU MUST EDIT THE MACHINE-DEPENDENT DEFINITIONS BELOW!!! *
  11    ************************************************************
  12 */
  13
  14 /*  File   : stdtod.c (Modified version of str2dbl.c)
  15     Author : Richard A. O'Keefe @ Quintus Computer Systems, Inc.
  16     Updated: Tuesday August 2nd, 1988
  17     Defines: double strtod (char *str, char**ptr)
  18 */
  19
  20 /*  This is an implementation of the strtod() function described in the
  21     System V manuals, with a different name to avoid linker problems.
  22     All that str2dbl() does itself is check that the argument is well-formed
  23     and is in range.  It leaves the work of conversion to atof(), which is
  24     assumed to exist and deliver correct results (if they can be represented).
  25
  26     There are two reasons why this should be provided to the net:
  27     (a) some UNIX systems do not yet have strtod(), or do not have it
  28     available in the BSD "universe" (but they do have atof()).
  29     (b) some of the UNIX systems that *do* have it get it wrong.
  30     (some crash with large arguments, some assign the wrong *ptr value).
  31     There is a reason why *we* are providing it: we need a correct version
  32     of strtod(), and if we give this one away maybe someone will look for
  33     mistakes in it and fix them for us (:-).
  34 */
  35
  36 /*  The following constants are machine-specific.  MD{MIN,MAX}EXPT are
  37     integers and MD{MIN,MAX}FRAC are strings such that
  38     0.${MDMAXFRAC}e${MDMAXEXPT} is the largest representable double,
  39     0.${MDMINFRAC}e${MDMINEXPT} is the smallest representable +ve double
  40     MD{MIN,MAX}FRAC must not have any trailing zeros.
  41     The values here are for IEEE-754 64-bit floats.
  42     It is not perfectly clear to me whether an IEEE infinity should be
  43     returned for overflow, nor what a portable way of writing one is,
  44     so HUGE is just 0.MAXFRAC*10**MAXEXPT (this seems still to be the
  45     UNIX convention).
  46
  47     I do know about <values.h>, but the whole point of this file is that
  48     we can't always trust that stuff to be there or to be correct.
  49 */
  50 static  int     MDMINEXPT       = -323;
  51 static  char    MDMINFRAC[]     = "494065645841246544";
  52 static  double  ZERO            = 0.0;
  53
  54 static  int     MDMAXEXPT       = 309;
  55 static  char    MDMAXFRAC[]     = "17976931348623157";
  56 static  double  HUGE            = 1.7976931348623157e308;
  57
  58 extern  double  atof(const char *);             /* Only called when result known to be ok */
  59
  60 #ifdef HAVE_ERRNO_H
  61 #include <errno.h>
  62 #endif
  63 extern  int     errno;
  64
  65 double strtod(char *str, char **ptr)
  66 {
  67     int sign, scale, dotseen;
  68     int esign, expt;
  69     char *save;
  70     register char *sp, *dp;
  71     register int c;
  72     char *buforg, *buflim;
  73     char buffer[64];                    /* 45-digit significant + */
  74                     /* 13-digit exponent */
  75     sp = str;
  76     while (*sp == ' ') sp++;
  77     sign = 1;
  78     if (*sp == '-') sign -= 2, sp++;
  79     dotseen = 0, scale = 0;
  80     dp = buffer;
  81     *dp++ = '0'; *dp++ = '.';
  82     buforg = dp, buflim = buffer+48;
  83     for (save = sp; (c = *sp); sp++)
  84         if (c == '.') {
  85         if (dotseen) break;
  86         dotseen++;
  87         } else
  88         if ((unsigned)(c-'0') > (unsigned)('9'-'0')) {
  89         break;
  90         } else
  91         if (c == '0') {
  92         if (dp != buforg) {
  93             /* This is not the first digit, so we want to keep it */
  94             if (dp < buflim) *dp++ = c;
  95             if (!dotseen) scale++;
  96         } else {
  97             /* No non-zero digits seen yet */
  98             /* If a . has been seen, scale must be adjusted */
  99             if (dotseen) scale--;
 100         }
 101         } else {
 102         /* This is a nonzero digit, so we want to keep it */
 103         if (dp < buflim) *dp++ = c;
 104         /* If it precedes a ., scale must be adjusted */
 105         if (!dotseen) scale++;
 106         }
 107     if (sp == save) {
 108         if (ptr) *ptr = str;
 109         errno = EDOM;                   /* what should this be? */
 110         return ZERO;
 111     }
 112
 113     while (dp > buforg && dp[-1] == '0') --dp;
 114     if (dp == buforg) *dp++ = '0';
 115     *dp = '\0';
 116     /*  Now the contents of buffer are
 117         +--+--------+-+--------+
 118         |0.|fraction|\|leftover|
 119         +--+--------+-+--------+
 120                      ^dp points here
 121         where fraction begins with 0 iff it is "0", and has at most
 122         45 digits in it, and leftover is at least 16 characters.
 123     */
 124     save = sp, expt = 0, esign = 1;
 125     do {
 126         c = *sp++;
 127         if (c != 'e' && c != 'E') break;
 128         c = *sp++;
 129         if (c == '-') esign -= 2, c = *sp++; else
 130         if (c == '+' /* || c == ' ' */ ) c = *sp++;
 131         if ((unsigned)(c-'0') > (unsigned)('9'-'0')) break;
 132         while (c == '0') c = *sp++;
 133         for (; (unsigned)(c-'0') <= (unsigned)('9'-'0'); c = *sp++)
 134         expt = expt*10 + c-'0';
 135         if (esign < 0) expt = -expt;
 136         save = sp-1;
 137     } while (0);
 138     if (ptr) *ptr = save;
 139     expt += scale;
 140     /*  Now the number is sign*0.fraction*10**expt  */
 141     errno = ERANGE;
 142     if (expt > MDMAXEXPT) {
 143         return HUGE*sign;
 144     } else
 145     if (expt == MDMAXEXPT) {
 146         if (strcmp(buforg, MDMAXFRAC) > 0) return HUGE*sign;
 147     } else
 148     if (expt < MDMINEXPT) {
 149         return ZERO*sign;
 150     } else
 151     if (expt == MDMINEXPT) {
 152         if (strcmp(buforg, MDMINFRAC) < 0) return ZERO*sign;
 153     }
 154     /*  We have now established that the number can be  */
 155     /*  represented without overflow or underflow  */
 156     (void) sprintf(dp, "E%d", expt);
 157     errno = 0;
 158     return atof(buffer)*sign;
 159 }