| 1 | /* |
| 2 | * strtod.c -- |
| 3 | * |
| 4 | * Source code for the "strtod" library procedure. |
| 5 | * |
| 6 | * Copyright 1988-1992 Regents of the University of California |
| 7 | * Permission to use, copy, modify, and distribute this |
| 8 | * software and its documentation for any purpose and without |
| 9 | * fee is hereby granted, provided that the above copyright |
| 10 | * notice appear in all copies. The University of California |
| 11 | * makes no representations about the suitability of this |
| 12 | * software for any purpose. It is provided "as is" without |
| 13 | * express or implied warranty. |
| 14 | */ |
| 15 | |
| 16 | #ifndef lint |
| 17 | static char rcsid[] = "$Header: /user6/ouster/tcl/compat/RCS/strtod.c,v 1.1 92/01/03 16:39:02 ouster Exp $ SPRITE (Berkeley)"; |
| 18 | #endif /* not lint */ |
| 19 | |
| 20 | #include <stdlib.h> |
| 21 | #include <ctype.h> |
| 22 | |
| 23 | #ifndef TRUE |
| 24 | #define TRUE 1 |
| 25 | #define FALSE 0 |
| 26 | #endif |
| 27 | #ifndef NULL |
| 28 | #define NULL 0 |
| 29 | #endif |
| 30 | |
| 31 | static int maxExponent = 511; /* Largest possible base 10 exponent. Any |
| 32 | * exponent larger than this will already |
| 33 | * produce underflow or overflow, so there's |
| 34 | * no need to worry about additional digits. |
| 35 | */ |
| 36 | static double powersOf10[] = { /* Table giving binary powers of 10. Entry */ |
| 37 | 10., /* is 10^2^i. Used to convert decimal */ |
| 38 | 100., /* exponents into floating-point numbers. */ |
| 39 | 1.0e4, |
| 40 | 1.0e8, |
| 41 | 1.0e16, |
| 42 | 1.0e32, |
| 43 | 1.0e64, |
| 44 | 1.0e128, |
| 45 | 1.0e256 |
| 46 | }; |
| 47 | \f |
| 48 | /* |
| 49 | *---------------------------------------------------------------------- |
| 50 | * |
| 51 | * strtod -- |
| 52 | * |
| 53 | * This procedure converts a floating-point number from an ASCII |
| 54 | * decimal representation to internal double-precision format. |
| 55 | * |
| 56 | * Results: |
| 57 | * The return value is the double-precision floating-point |
| 58 | * representation of the characters in string. If endPtr isn't |
| 59 | * NULL, then *endPtr is filled in with the address of the |
| 60 | * next character after the last one that was part of the |
| 61 | * floating-point number. |
| 62 | * |
| 63 | * Side effects: |
| 64 | * None. |
| 65 | * |
| 66 | *---------------------------------------------------------------------- |
| 67 | */ |
| 68 | |
| 69 | double |
| 70 | strtod(string, endPtr) |
| 71 | char *string; /* A decimal ASCII floating-point number, |
| 72 | * optionally preceded by white space. |
| 73 | * Must have form "-I.FE-X", where I is the |
| 74 | * integer part of the mantissa, F is the |
| 75 | * fractional part of the mantissa, and X |
| 76 | * is the exponent. Either of the signs |
| 77 | * may be "+", "-", or omitted. Either I |
| 78 | * or F may be omitted, or both. The decimal |
| 79 | * point isn't necessary unless F is present. |
| 80 | * The "E" may actually be an "e". E and X |
| 81 | * may both be omitted (but not just one). |
| 82 | */ |
| 83 | char **endPtr; /* If non-NULL, store terminating character's |
| 84 | * address here. */ |
| 85 | { |
| 86 | int sign, expSign = FALSE; |
| 87 | double fraction, dblExp, *d; |
| 88 | register char *p, c; |
| 89 | int exp = 0; /* Exponent read from "EX" field. */ |
| 90 | int fracExp = 0; /* Exponent that derives from the fractional |
| 91 | * part. Under normal circumstatnces, it is |
| 92 | * the negative of the number of digits in F. |
| 93 | * However, if I is very long, the last digits |
| 94 | * of I get dropped (otherwise a long I with a |
| 95 | * large negative exponent could cause an |
| 96 | * unnecessary overflow on I alone). In this |
| 97 | * case, fracExp is incremented one for each |
| 98 | * dropped digit. |
| 99 | */ |
| 100 | int mantSize; /* Number of digits in mantissa. */ |
| 101 | int decPt; /* Number of mantissa digits BEFORE decimal |
| 102 | * point. |
| 103 | */ |
| 104 | char *pExp; /* Temporarily holds location of exponent |
| 105 | * in string. |
| 106 | */ |
| 107 | |
| 108 | /* |
| 109 | * Strip off leading blanks and check for a sign. |
| 110 | */ |
| 111 | |
| 112 | p = string; |
| 113 | while (isspace(*p)) { |
| 114 | p += 1; |
| 115 | } |
| 116 | if (*p == '-') { |
| 117 | sign = TRUE; |
| 118 | p += 1; |
| 119 | } else { |
| 120 | if (*p == '+') { |
| 121 | p += 1; |
| 122 | } |
| 123 | sign = FALSE; |
| 124 | } |
| 125 | |
| 126 | /* |
| 127 | * Count the number of digits in the mantissa (including the decimal |
| 128 | * point), and also locate the decimal point. |
| 129 | */ |
| 130 | |
| 131 | decPt = -1; |
| 132 | for (mantSize = 0; ; mantSize += 1) |
| 133 | { |
| 134 | c = *p; |
| 135 | if (!isdigit(c)) { |
| 136 | if ((c != '.') || (decPt >= 0)) { |
| 137 | break; |
| 138 | } |
| 139 | decPt = mantSize; |
| 140 | } |
| 141 | p += 1; |
| 142 | } |
| 143 | |
| 144 | /* |
| 145 | * Now suck up the digits in the mantissa. Use two integers to |
| 146 | * collect 9 digits each (this is faster than using floating-point). |
| 147 | * If the mantissa has more than 18 digits, ignore the extras, since |
| 148 | * they can't affect the value anyway. |
| 149 | */ |
| 150 | |
| 151 | pExp = p; |
| 152 | p -= mantSize; |
| 153 | if (decPt < 0) { |
| 154 | decPt = mantSize; |
| 155 | } else { |
| 156 | mantSize -= 1; /* One of the digits was the point. */ |
| 157 | } |
| 158 | if (mantSize > 18) { |
| 159 | fracExp = decPt - 18; |
| 160 | mantSize = 18; |
| 161 | } else { |
| 162 | fracExp = decPt - mantSize; |
| 163 | } |
| 164 | if (mantSize == 0) { |
| 165 | fraction = 0.0; |
| 166 | p = string; |
| 167 | goto done; |
| 168 | } else { |
| 169 | int frac1, frac2; |
| 170 | frac1 = 0; |
| 171 | for ( ; mantSize > 9; mantSize -= 1) |
| 172 | { |
| 173 | c = *p; |
| 174 | p += 1; |
| 175 | if (c == '.') { |
| 176 | c = *p; |
| 177 | p += 1; |
| 178 | } |
| 179 | frac1 = 10*frac1 + (c - '0'); |
| 180 | } |
| 181 | frac2 = 0; |
| 182 | for (; mantSize > 0; mantSize -= 1) |
| 183 | { |
| 184 | c = *p; |
| 185 | p += 1; |
| 186 | if (c == '.') { |
| 187 | c = *p; |
| 188 | p += 1; |
| 189 | } |
| 190 | frac2 = 10*frac2 + (c - '0'); |
| 191 | } |
| 192 | fraction = (1.0e9 * frac1) + frac2; |
| 193 | } |
| 194 | |
| 195 | /* |
| 196 | * Skim off the exponent. |
| 197 | */ |
| 198 | |
| 199 | p = pExp; |
| 200 | if ((*p == 'E') || (*p == 'e')) { |
| 201 | p += 1; |
| 202 | if (*p == '-') { |
| 203 | expSign = TRUE; |
| 204 | p += 1; |
| 205 | } else { |
| 206 | if (*p == '+') { |
| 207 | p += 1; |
| 208 | } |
| 209 | expSign = FALSE; |
| 210 | } |
| 211 | while (isdigit(*p)) { |
| 212 | exp = exp * 10 + (*p - '0'); |
| 213 | p += 1; |
| 214 | } |
| 215 | } |
| 216 | if (expSign) { |
| 217 | exp = fracExp - exp; |
| 218 | } else { |
| 219 | exp = fracExp + exp; |
| 220 | } |
| 221 | |
| 222 | /* |
| 223 | * Generate a floating-point number that represents the exponent. |
| 224 | * Do this by processing the exponent one bit at a time to combine |
| 225 | * many powers of 2 of 10. Then combine the exponent with the |
| 226 | * fraction. |
| 227 | */ |
| 228 | |
| 229 | if (exp < 0) { |
| 230 | expSign = TRUE; |
| 231 | exp = -exp; |
| 232 | } else { |
| 233 | expSign = FALSE; |
| 234 | } |
| 235 | if (exp > maxExponent) { |
| 236 | exp = maxExponent; |
| 237 | } |
| 238 | dblExp = 1.0; |
| 239 | for (d = powersOf10; exp != 0; exp >>= 1, d += 1) { |
| 240 | if (exp & 01) { |
| 241 | dblExp *= *d; |
| 242 | } |
| 243 | } |
| 244 | if (expSign) { |
| 245 | fraction /= dblExp; |
| 246 | } else { |
| 247 | fraction *= dblExp; |
| 248 | } |
| 249 | |
| 250 | done: |
| 251 | if (endPtr != NULL) { |
| 252 | *endPtr = p; |
| 253 | } |
| 254 | |
| 255 | if (sign) { |
| 256 | return -fraction; |
| 257 | } |
| 258 | return fraction; |
| 259 | } |