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Guido van Rossum23d5cde1992-01-14 18:42:23 +00001/* comp.sources.misc strtod(), as posted in comp.lang.tcl,
2 with bugfix for "123000.0" and acceptance of space after 'e' sign nuked.
Guido van Rossum753e2bf1991-04-16 08:45:40 +00003
Guido van Rossum23d5cde1992-01-14 18:42:23 +00004 ************************************************************
5 * YOU MUST EDIT THE MACHINE-DEPENDENT DEFINITIONS BELOW!!! *
6 ************************************************************
7*/
Guido van Rossum5afc7471991-12-31 13:15:19 +00008
Guido van Rossum23d5cde1992-01-14 18:42:23 +00009/* File : stdtod.c (Modified version of str2dbl.c)
10 Author : Richard A. O'Keefe @ Quintus Computer Systems, Inc.
11 Updated: Tuesday August 2nd, 1988
12 Defines: double strtod (char *str, char**ptr)
13*/
Guido van Rossum753e2bf1991-04-16 08:45:40 +000014
Guido van Rossum23d5cde1992-01-14 18:42:23 +000015/* This is an implementation of the strtod() function described in the
16 System V manuals, with a different name to avoid linker problems.
17 All that str2dbl() does itself is check that the argument is well-formed
18 and is in range. It leaves the work of conversion to atof(), which is
19 assumed to exist and deliver correct results (if they can be represented).
Guido van Rossum5afc7471991-12-31 13:15:19 +000020
Guido van Rossum23d5cde1992-01-14 18:42:23 +000021 There are two reasons why this should be provided to the net:
22 (a) some UNIX systems do not yet have strtod(), or do not have it
23 available in the BSD "universe" (but they do have atof()).
24 (b) some of the UNIX systems that *do* have it get it wrong.
25 (some crash with large arguments, some assign the wrong *ptr value).
26 There is a reason why *we* are providing it: we need a correct version
27 of strtod(), and if we give this one away maybe someone will look for
28 mistakes in it and fix them for us (:-).
29*/
30
31/* The following constants are machine-specific. MD{MIN,MAX}EXPT are
32 integers and MD{MIN,MAX}FRAC are strings such that
33 0.${MDMAXFRAC}e${MDMAXEXPT} is the largest representable double,
34 0.${MDMINFRAC}e${MDMINEXPT} is the smallest representable +ve double
35 MD{MIN,MAX}FRAC must not have any trailing zeros.
36 The values here are for IEEE-754 64-bit floats.
37 It is not perfectly clear to me whether an IEEE infinity should be
38 returned for overflow, nor what a portable way of writing one is,
39 so HUGE is just 0.MAXFRAC*10**MAXEXPT (this seems still to be the
40 UNIX convention).
41
42 I do know about <values.h>, but the whole point of this file is that
43 we can't always trust that stuff to be there or to be correct.
44*/
45static int MDMINEXPT = {-323};
46static char MDMINFRAC[] = "494065645841246544";
47static double ZERO = 0.0;
48
49static int MDMAXEXPT = { 309};
Guido van Rossumdcc6ef21992-03-27 17:30:32 +000050static char MDMAXFRAC[] = "17976931348623157";
51static double HUGE = 1.7976931348623157e308;
Guido van Rossum23d5cde1992-01-14 18:42:23 +000052
53extern double atof(); /* Only called when result known to be ok */
54
55#include <errno.h>
56extern int errno;
57
58double strtod(str, ptr)
59 char *str;
60 char **ptr;
61 {
62 int sign, scale, dotseen;
63 int esign, expt;
64 char *save;
65 register char *sp, *dp;
66 register int c;
67 char *buforg, *buflim;
68 char buffer[64]; /* 45-digit significand + */
69 /* 13-digit exponent */
70 sp = str;
71 while (*sp == ' ') sp++;
72 sign = 1;
73 if (*sp == '-') sign -= 2, sp++;
74 dotseen = 0, scale = 0;
75 dp = buffer;
76 *dp++ = '0'; *dp++ = '.';
77 buforg = dp, buflim = buffer+48;
78 for (save = sp; c = *sp; sp++)
79 if (c == '.') {
80 if (dotseen) break;
81 dotseen++;
82 } else
83 if ((unsigned)(c-'0') > (unsigned)('9'-'0')) {
84 break;
85 } else
86 if (c == '0') {
87 if (dp != buforg) {
88 /* This is not the first digit, so we want to keep it */
89 if (dp < buflim) *dp++ = c;
90 if (!dotseen) scale++;
91 } else {
92 /* No non-zero digits seen yet */
93 /* If a . has been seen, scale must be adjusted */
94 if (dotseen) scale--;
95 }
96 } else {
97 /* This is a nonzero digit, so we want to keep it */
98 if (dp < buflim) *dp++ = c;
99 /* If it precedes a ., scale must be adjusted */
100 if (!dotseen) scale++;
101 }
102 if (sp == save) {
103 if (ptr) *ptr = str;
104 errno = EDOM; /* what should this be? */
105 return ZERO;
106 }
Guido van Rossum5afc7471991-12-31 13:15:19 +0000107
Guido van Rossum23d5cde1992-01-14 18:42:23 +0000108 while (dp > buforg && dp[-1] == '0') --dp;
109 if (dp == buforg) *dp++ = '0';
110 *dp = '\0';
111 /* Now the contents of buffer are
112 +--+--------+-+--------+
113 |0.|fraction|\|leftover|
114 +--+--------+-+--------+
115 ^dp points here
116 where fraction begins with 0 iff it is "0", and has at most
117 45 digits in it, and leftover is at least 16 characters.
118 */
119 save = sp, expt = 0, esign = 1;
120 do {
121 c = *sp++;
122 if (c != 'e' && c != 'E') break;
123 c = *sp++;
124 if (c == '-') esign -= 2, c = *sp++; else
125 if (c == '+' /* || c == ' ' */ ) c = *sp++;
126 if ((unsigned)(c-'0') > (unsigned)('9'-'0')) break;
127 while (c == '0') c = *sp++;
128 for (; (unsigned)(c-'0') <= (unsigned)('9'-'0'); c = *sp++)
129 expt = expt*10 + c-'0';
130 if (esign < 0) expt = -expt;
131 save = sp-1;
132 } while (0);
133 if (ptr) *ptr = save;
134 expt += scale;
135 /* Now the number is sign*0.fraction*10**expt */
136 errno = ERANGE;
137 if (expt > MDMAXEXPT) {
138 return HUGE*sign;
139 } else
140 if (expt == MDMAXEXPT) {
141 if (strcmp(buforg, MDMAXFRAC) > 0) return HUGE*sign;
142 } else
143 if (expt < MDMINEXPT) {
144 return ZERO*sign;
145 } else
146 if (expt == MDMINEXPT) {
147 if (strcmp(buforg, MDMINFRAC) < 0) return ZERO*sign;
148 }
149 /* We have now established that the number can be */
150 /* represented without overflow or underflow */
151 (void) sprintf(dp, "E%d", expt);
152 errno = 0;
153 return atof(buffer)*sign;
154 }