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Guido van Rossum 1992-01-14 18:42:23 +00:00
parent 77b4604eaf
commit 23d5cdebac
1 changed files with 149 additions and 17 deletions
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166
Python/strtod.c
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@ -1,22 +1,154 @@
/* This is not a proper strtod() implementation, but sufficient for Python.
Python won't detect floating point constant overflow, though. */
/* comp.sources.misc strtod(), as posted in comp.lang.tcl,
with bugfix for "123000.0" and acceptance of space after 'e' sign nuked.
extern int errno;
************************************************************
* YOU MUST EDIT THE MACHINE-DEPENDENT DEFINITIONS BELOW!!! *
************************************************************
*/
extern int strlen();
extern double atof();
/* 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)
*/
double
strtod(p, pp)
char *p;
char **pp;
{
double res;
/* 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).
if (pp)
*pp = p + strlen(p);
res = atof(p);
errno = 0;
return res;
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[] = "17976931348623147";
static double HUGE = 1.7976931348623147e308;
extern double atof(); /* Only called when result known to be ok */
#include <errno.h>
extern int errno;
double strtod(str, ptr)
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 significand + */
/* 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;
}