summaryrefslogtreecommitdiffstats
path: root/compat/strtod.c
blob: 063e175f4dd0a5bc02cf494075de25afa0077e88 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
/* 
 * strtod.c --
 *
 *	Source code for the "strtod" library procedure.
 *
 * Copyright (c) 1988-1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: strtod.c,v 1.6 2002/02/25 14:26:12 dgp Exp $
 */

#include "tclInt.h"
#include "tclPort.h"
#include <ctype.h>

#ifndef TRUE
#define TRUE 1
#define FALSE 0
#endif
#ifndef NULL
#define NULL 0
#endif

static int maxExponent = 511;	/* Largest possible base 10 exponent.  Any
				 * exponent larger than this will already
				 * produce underflow or overflow, so there's
				 * no need to worry about additional digits.
				 */
static double powersOf10[] = {	/* Table giving binary powers of 10.  Entry */
    10.,			/* is 10^2^i.  Used to convert decimal */
    100.,			/* exponents into floating-point numbers. */
    1.0e4,
    1.0e8,
    1.0e16,
    1.0e32,
    1.0e64,
    1.0e128,
    1.0e256
};

/*
 *----------------------------------------------------------------------
 *
 * strtod --
 *
 *	This procedure converts a floating-point number from an ASCII
 *	decimal representation to internal double-precision format.
 *
 * Results:
 *	The return value is the double-precision floating-point
 *	representation of the characters in string.  If endPtr isn't
 *	NULL, then *endPtr is filled in with the address of the
 *	next character after the last one that was part of the
 *	floating-point number.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

double
strtod(string, endPtr)
    CONST char *string;		/* A decimal ASCII floating-point number,
				 * optionally preceded by white space.
				 * Must have form "-I.FE-X", where I is the
				 * integer part of the mantissa, F is the
				 * fractional part of the mantissa, and X
				 * is the exponent.  Either of the signs
				 * may be "+", "-", or omitted.  Either I
				 * or F may be omitted, or both.  The decimal
				 * point isn't necessary unless F is present.
				 * The "E" may actually be an "e".  E and X
				 * may both be omitted (but not just one).
				 */
    char **endPtr;		/* If non-NULL, store terminating character's
				 * address here. */
{
    int sign, expSign = FALSE;
    double fraction, dblExp, *d;
    register CONST char *p;
    register int c;
    int exp = 0;		/* Exponent read from "EX" field. */
    int fracExp = 0;		/* Exponent that derives from the fractional
				 * part.  Under normal circumstatnces, it is
				 * the negative of the number of digits in F.
				 * However, if I is very long, the last digits
				 * of I get dropped (otherwise a long I with a
				 * large negative exponent could cause an
				 * unnecessary overflow on I alone).  In this
				 * case, fracExp is incremented one for each
				 * dropped digit. */
    int mantSize;		/* Number of digits in mantissa. */
    int decPt;			/* Number of mantissa digits BEFORE decimal
				 * point. */
    CONST char *pExp;		/* Temporarily holds location of exponent
				 * in string. */

    /*
     * Strip off leading blanks and check for a sign.
     */

    p = string;
    while (isspace(UCHAR(*p))) {
	p += 1;
    }
    if (*p == '-') {
	sign = TRUE;
	p += 1;
    } else {
	if (*p == '+') {
	    p += 1;
	}
	sign = FALSE;
    }

    /*
     * Count the number of digits in the mantissa (including the decimal
     * point), and also locate the decimal point.
     */

    decPt = -1;
    for (mantSize = 0; ; mantSize += 1)
    {
	c = *p;
	if (!isdigit(c)) {
	    if ((c != '.') || (decPt >= 0)) {
		break;
	    }
	    decPt = mantSize;
	}
	p += 1;
    }

    /*
     * Now suck up the digits in the mantissa.  Use two integers to
     * collect 9 digits each (this is faster than using floating-point).
     * If the mantissa has more than 18 digits, ignore the extras, since
     * they can't affect the value anyway.
     */
    
    pExp  = p;
    p -= mantSize;
    if (decPt < 0) {
	decPt = mantSize;
    } else {
	mantSize -= 1;			/* One of the digits was the point. */
    }
    if (mantSize > 18) {
	fracExp = decPt - 18;
	mantSize = 18;
    } else {
	fracExp = decPt - mantSize;
    }
    if (mantSize == 0) {
	fraction = 0.0;
	p = string;
	goto done;
    } else {
	int frac1, frac2;
	frac1 = 0;
	for ( ; mantSize > 9; mantSize -= 1)
	{
	    c = *p;
	    p += 1;
	    if (c == '.') {
		c = *p;
		p += 1;
	    }
	    frac1 = 10*frac1 + (c - '0');
	}
	frac2 = 0;
	for (; mantSize > 0; mantSize -= 1)
	{
	    c = *p;
	    p += 1;
	    if (c == '.') {
		c = *p;
		p += 1;
	    }
	    frac2 = 10*frac2 + (c - '0');
	}
	fraction = (1.0e9 * frac1) + frac2;
    }

    /*
     * Skim off the exponent.
     */

    p = pExp;
    if ((*p == 'E') || (*p == 'e')) {
	p += 1;
	if (*p == '-') {
	    expSign = TRUE;
	    p += 1;
	} else {
	    if (*p == '+') {
		p += 1;
	    }
	    expSign = FALSE;
	}
	if (!isdigit(UCHAR(*p))) {
	    p = pExp;
	    goto done;
	}
	while (isdigit(UCHAR(*p))) {
	    exp = exp * 10 + (*p - '0');
	    p += 1;
	}
    }
    if (expSign) {
	exp = fracExp - exp;
    } else {
	exp = fracExp + exp;
    }

    /*
     * Generate a floating-point number that represents the exponent.
     * Do this by processing the exponent one bit at a time to combine
     * many powers of 2 of 10. Then combine the exponent with the
     * fraction.
     */
    
    if (exp < 0) {
	expSign = TRUE;
	exp = -exp;
    } else {
	expSign = FALSE;
    }
    if (exp > maxExponent) {
	exp = maxExponent;
	errno = ERANGE;
    }
    dblExp = 1.0;
    for (d = powersOf10; exp != 0; exp >>= 1, d += 1) {
	if (exp & 01) {
	    dblExp *= *d;
	}
    }
    if (expSign) {
	fraction /= dblExp;
    } else {
	fraction *= dblExp;
    }

done:
    if (endPtr != NULL) {
	*endPtr = (char *) p;
    }

    if (sign) {
	return -fraction;
    }
    return fraction;
}