1 /*
2 * Copyright (c) 1988-1993 The Regents of the University of California.
3 * Copyright (c) 1994 Sun Microsystems, Inc.
4 *
5 * Permission to use, copy, modify, and distribute this
6 * software and its documentation for any purpose and without
7 * fee is hereby granted, provided that the above copyright
8 * notice appear in all copies. The University of California
9 * makes no representations about the suitability of this
10 * software for any purpose. It is provided "as is" without
11 * express or implied warranty.
12 *
13 */
14
15 #include <stdlib.h>
16 #include <ctype.h>
17 #include <errno.h>
18
19 static
20 const int maxExponent = 511; /* Largest possible base 10 exponent. Any
21 * exponent larger than this will already
22 * produce underflow or overflow, so there's
23 * no need to worry about additional digits.
24 */
25
26 static
27 const double powersOf10[] = { /* Table giving binary powers of 10. Entry */
28 10., /* is 10^2^i. Used to convert decimal */
29 100., /* exponents into floating-point numbers. */
30 1.0e4,
31 1.0e8,
32 1.0e16,
33 1.0e32,
34 1.0e64,
35 1.0e128,
36 1.0e256
37 };
38
39 /*
40 *----------------------------------------------------------------------
41 *
42 * strtod --
43 *
44 * This procedure converts a floating-point number from an ASCII
45 * decimal representation to internal double-precision format.
46 *
47 * Results:
48 * The return value is the double-precision floating-point
49 * representation of the characters in string. If endPtr isn't
50 * NULL, then *endPtr is filled in with the address of the
51 * next character after the last one that was part of the
52 * floating-point number.
53 *
54 * Side effects:
55 * None.
56 *
57 *----------------------------------------------------------------------
58 */
59
60 double
ass_strtod(const char * string,char ** endPtr)61 ass_strtod(
62 const char *string, /* A decimal ASCII floating-point number,
63 * optionally preceded by white space.
64 * Must have form "-I.FE-X", where I is the
65 * integer part of the mantissa, F is the
66 * fractional part of the mantissa, and X
67 * is the exponent. Either of the signs
68 * may be "+", "-", or omitted. Either I
69 * or F may be omitted, or both. The decimal
70 * point isn't necessary unless F is present.
71 * The "E" may actually be an "e". E and X
72 * may both be omitted (but not just one).
73 */
74 char **endPtr /* If non-NULL, store terminating character's
75 * address here. */
76 )
77 {
78 int sign, expSign = 0;
79 double fraction, dblExp, *d;
80 register const char *p;
81 register int c;
82 int exp = 0; /* Exponent read from "EX" field. */
83 int fracExp = 0; /* Exponent that derives from the fractional
84 * part. Under normal circumstatnces, it is
85 * the negative of the number of digits in F.
86 * However, if I is very long, the last digits
87 * of I get dropped (otherwise a long I with a
88 * large negative exponent could cause an
89 * unnecessary overflow on I alone). In this
90 * case, fracExp is incremented one for each
91 * dropped digit. */
92 int mantSize; /* Number of digits in mantissa. */
93 int decPt; /* Number of mantissa digits BEFORE decimal
94 * point. */
95 const char *pExp; /* Temporarily holds location of exponent
96 * in string. */
97
98 /*
99 * Strip off leading blanks and check for a sign.
100 */
101
102 p = string;
103 while (isspace(*p)) {
104 p += 1;
105 }
106 if (*p == '-') {
107 sign = 1;
108 p += 1;
109 } else {
110 if (*p == '+') {
111 p += 1;
112 }
113 sign = 0;
114 }
115
116 /*
117 * Count the number of digits in the mantissa (including the decimal
118 * point), and also locate the decimal point.
119 */
120
121 decPt = -1;
122 for (mantSize = 0; ; mantSize += 1)
123 {
124 c = *p;
125 if (!isdigit(c)) {
126 if ((c != '.') || (decPt >= 0)) {
127 break;
128 }
129 decPt = mantSize;
130 }
131 p += 1;
132 }
133
134 /*
135 * Now suck up the digits in the mantissa. Use two integers to
136 * collect 9 digits each (this is faster than using floating-point).
137 * If the mantissa has more than 18 digits, ignore the extras, since
138 * they can't affect the value anyway.
139 */
140
141 pExp = p;
142 p -= mantSize;
143 if (decPt < 0) {
144 decPt = mantSize;
145 } else {
146 mantSize -= 1; /* One of the digits was the point. */
147 }
148 if (mantSize > 18) {
149 fracExp = decPt - 18;
150 mantSize = 18;
151 } else {
152 fracExp = decPt - mantSize;
153 }
154 if (mantSize == 0) {
155 fraction = 0.0;
156 p = string;
157 goto done;
158 } else {
159 int frac1, frac2;
160 frac1 = 0;
161 for ( ; mantSize > 9; mantSize -= 1)
162 {
163 c = *p;
164 p += 1;
165 if (c == '.') {
166 c = *p;
167 p += 1;
168 }
169 frac1 = 10*frac1 + (c - '0');
170 }
171 frac2 = 0;
172 for (; mantSize > 0; mantSize -= 1)
173 {
174 c = *p;
175 p += 1;
176 if (c == '.') {
177 c = *p;
178 p += 1;
179 }
180 frac2 = 10*frac2 + (c - '0');
181 }
182 fraction = (1.0e9 * frac1) + frac2;
183 }
184
185 /*
186 * Skim off the exponent.
187 */
188
189 p = pExp;
190 if ((*p == 'E') || (*p == 'e')) {
191 p += 1;
192 if (*p == '-') {
193 expSign = 1;
194 p += 1;
195 } else {
196 if (*p == '+') {
197 p += 1;
198 }
199 expSign = 0;
200 }
201 while (isdigit(*p)) {
202 exp = exp * 10 + (*p - '0');
203 p += 1;
204 }
205 }
206 if (expSign) {
207 exp = fracExp - exp;
208 } else {
209 exp = fracExp + exp;
210 }
211
212 /*
213 * Generate a floating-point number that represents the exponent.
214 * Do this by processing the exponent one bit at a time to combine
215 * many powers of 2 of 10. Then combine the exponent with the
216 * fraction.
217 */
218
219 if (exp < 0) {
220 expSign = 1;
221 exp = -exp;
222 } else {
223 expSign = 0;
224 }
225 if (exp > maxExponent) {
226 exp = maxExponent;
227 errno = ERANGE;
228 }
229 dblExp = 1.0;
230 for (d = (double *) powersOf10; exp != 0; exp >>= 1, d += 1) {
231 if (exp & 01) {
232 dblExp *= *d;
233 }
234 }
235 if (expSign) {
236 fraction /= dblExp;
237 } else {
238 fraction *= dblExp;
239 }
240
241 done:
242 if (endPtr != NULL) {
243 *endPtr = (char *) p;
244 }
245
246 if (sign) {
247 return -fraction;
248 }
249 return fraction;
250 }
251