ref: a7f5ecaf636e38f407c951d0e86dcc4c4f424bd6
dir: /sys/src/cmd/python/Python/strtod.c/
#include "pyconfig.h"
/* comp.sources.misc strtod(), as posted in comp.lang.tcl,
with bugfix for "123000.0" and acceptance of space after 'e' sign nuked.
************************************************************
* YOU MUST EDIT THE MACHINE-DEPENDENT DEFINITIONS BELOW!!! *
************************************************************
*/
/* File : stdtod.c (Modified version of str2dbl.c)
Author : Richard A. O'Keefe @ Quintus Computer Systems, Inc.
Updated: Tuesday August 2nd, 1988
Defines: double strtod (char *str, char**ptr)
*/
/* This is an implementation of the strtod() function described in the
System V manuals, with a different name to avoid linker problems.
All that str2dbl() does itself is check that the argument is well-formed
and is in range. It leaves the work of conversion to atof(), which is
assumed to exist and deliver correct results (if they can be represented).
There are two reasons why this should be provided to the net:
(a) some UNIX systems do not yet have strtod(), or do not have it
available in the BSD "universe" (but they do have atof()).
(b) some of the UNIX systems that *do* have it get it wrong.
(some crash with large arguments, some assign the wrong *ptr value).
There is a reason why *we* are providing it: we need a correct version
of strtod(), and if we give this one away maybe someone will look for
mistakes in it and fix them for us (:-).
*/
/* The following constants are machine-specific. MD{MIN,MAX}EXPT are
integers and MD{MIN,MAX}FRAC are strings such that
0.${MDMAXFRAC}e${MDMAXEXPT} is the largest representable double,
0.${MDMINFRAC}e${MDMINEXPT} is the smallest representable +ve double
MD{MIN,MAX}FRAC must not have any trailing zeros.
The values here are for IEEE-754 64-bit floats.
It is not perfectly clear to me whether an IEEE infinity should be
returned for overflow, nor what a portable way of writing one is,
so HUGE is just 0.MAXFRAC*10**MAXEXPT (this seems still to be the
UNIX convention).
I do know about <values.h>, but the whole point of this file is that
we can't always trust that stuff to be there or to be correct.
*/
static int MDMINEXPT = {-323};
static char MDMINFRAC[] = "494065645841246544";
static double ZERO = 0.0;
static int MDMAXEXPT = { 309};
static char MDMAXFRAC[] = "17976931348623157";
static double HUGE = 1.7976931348623157e308;
extern double atof(const char *); /* Only called when result known to be ok */
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
extern int errno;
double strtod(char *str, char **ptr)
{
int sign, scale, dotseen;
int esign, expt;
char *save;
register char *sp, *dp;
register int c;
char *buforg, *buflim;
char buffer[64]; /* 45-digit significant + */
/* 13-digit exponent */
sp = str;
while (*sp == ' ') sp++;
sign = 1;
if (*sp == '-') sign -= 2, sp++;
dotseen = 0, scale = 0;
dp = buffer;
*dp++ = '0'; *dp++ = '.';
buforg = dp, buflim = buffer+48;
for (save = sp; c = *sp; sp++)
if (c == '.') {
if (dotseen) break;
dotseen++;
} else
if ((unsigned)(c-'0') > (unsigned)('9'-'0')) {
break;
} else
if (c == '0') {
if (dp != buforg) {
/* This is not the first digit, so we want to keep it */
if (dp < buflim) *dp++ = c;
if (!dotseen) scale++;
} else {
/* No non-zero digits seen yet */
/* If a . has been seen, scale must be adjusted */
if (dotseen) scale--;
}
} else {
/* This is a nonzero digit, so we want to keep it */
if (dp < buflim) *dp++ = c;
/* If it precedes a ., scale must be adjusted */
if (!dotseen) scale++;
}
if (sp == save) {
if (ptr) *ptr = str;
errno = EDOM; /* what should this be? */
return ZERO;
}
while (dp > buforg && dp[-1] == '0') --dp;
if (dp == buforg) *dp++ = '0';
*dp = '\0';
/* Now the contents of buffer are
+--+--------+-+--------+
|0.|fraction|\|leftover|
+--+--------+-+--------+
^dp points here
where fraction begins with 0 iff it is "0", and has at most
45 digits in it, and leftover is at least 16 characters.
*/
save = sp, expt = 0, esign = 1;
do {
c = *sp++;
if (c != 'e' && c != 'E') break;
c = *sp++;
if (c == '-') esign -= 2, c = *sp++; else
if (c == '+' /* || c == ' ' */ ) c = *sp++;
if ((unsigned)(c-'0') > (unsigned)('9'-'0')) break;
while (c == '0') c = *sp++;
for (; (unsigned)(c-'0') <= (unsigned)('9'-'0'); c = *sp++)
expt = expt*10 + c-'0';
if (esign < 0) expt = -expt;
save = sp-1;
} while (0);
if (ptr) *ptr = save;
expt += scale;
/* Now the number is sign*0.fraction*10**expt */
errno = ERANGE;
if (expt > MDMAXEXPT) {
return HUGE*sign;
} else
if (expt == MDMAXEXPT) {
if (strcmp(buforg, MDMAXFRAC) > 0) return HUGE*sign;
} else
if (expt < MDMINEXPT) {
return ZERO*sign;
} else
if (expt == MDMINEXPT) {
if (strcmp(buforg, MDMINFRAC) < 0) return ZERO*sign;
}
/* We have now established that the number can be */
/* represented without overflow or underflow */
(void) sprintf(dp, "E%d", expt);
errno = 0;
return atof(buffer)*sign;
}