247 lines
7 KiB
C
247 lines
7 KiB
C
/*
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* Copyright (c) 1988-1993 The Regents of the University of California.
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* Copyright (c) 1994 Sun Microsystems, Inc.
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*
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* Permission to use, copy, modify, and distribute this
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* software and its documentation for any purpose and without
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* fee is hereby granted, provided that the above copyright
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* notice appear in all copies. The University of California
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* makes no representations about the suitability of this
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* software for any purpose. It is provided "as is" without
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* express or implied warranty.
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*
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*/
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#include <stdlib.h>
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#include <ctype.h>
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#include <errno.h>
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static int maxExponent = 511; /* Largest possible base 10 exponent. Any
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* exponent larger than this will already
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* produce underflow or overflow, so there's
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* no need to worry about additional digits.
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*/
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static double powersOf10[] = { /* Table giving binary powers of 10. Entry */
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10., /* is 10^2^i. Used to convert decimal */
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100., /* exponents into floating-point numbers. */
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1.0e4,
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1.0e8,
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1.0e16,
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1.0e32,
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1.0e64,
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1.0e128,
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1.0e256
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};
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/*
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*----------------------------------------------------------------------
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*
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* strtod --
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*
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* This procedure converts a floating-point number from an ASCII
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* decimal representation to internal double-precision format.
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*
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* Results:
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* The return value is the double-precision floating-point
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* representation of the characters in string. If endPtr isn't
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* NULL, then *endPtr is filled in with the address of the
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* next character after the last one that was part of the
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* floating-point number.
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*
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* Side effects:
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* None.
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*
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*----------------------------------------------------------------------
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*/
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double
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ass_strtod(string, endPtr)
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const char *string; /* A decimal ASCII floating-point number,
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* optionally preceded by white space.
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* Must have form "-I.FE-X", where I is the
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* integer part of the mantissa, F is the
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* fractional part of the mantissa, and X
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* is the exponent. Either of the signs
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* may be "+", "-", or omitted. Either I
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* or F may be omitted, or both. The decimal
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* point isn't necessary unless F is present.
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* The "E" may actually be an "e". E and X
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* may both be omitted (but not just one).
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*/
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char **endPtr; /* If non-NULL, store terminating character's
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* address here. */
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{
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int sign, expSign = 0;
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double fraction, dblExp, *d;
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register const char *p;
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register int c;
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int exp = 0; /* Exponent read from "EX" field. */
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int fracExp = 0; /* Exponent that derives from the fractional
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* part. Under normal circumstatnces, it is
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* the negative of the number of digits in F.
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* However, if I is very long, the last digits
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* of I get dropped (otherwise a long I with a
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* large negative exponent could cause an
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* unnecessary overflow on I alone). In this
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* case, fracExp is incremented one for each
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* dropped digit. */
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int mantSize; /* Number of digits in mantissa. */
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int decPt; /* Number of mantissa digits BEFORE decimal
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* point. */
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const char *pExp; /* Temporarily holds location of exponent
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* in string. */
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/*
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* Strip off leading blanks and check for a sign.
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*/
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p = string;
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while (isspace(*p)) {
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p += 1;
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}
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if (*p == '-') {
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sign = 1;
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p += 1;
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} else {
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if (*p == '+') {
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p += 1;
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}
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sign = 0;
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}
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/*
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* Count the number of digits in the mantissa (including the decimal
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* point), and also locate the decimal point.
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*/
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decPt = -1;
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for (mantSize = 0; ; mantSize += 1)
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{
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c = *p;
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if (!isdigit(c)) {
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if ((c != '.') || (decPt >= 0)) {
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break;
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}
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decPt = mantSize;
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}
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p += 1;
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}
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/*
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* Now suck up the digits in the mantissa. Use two integers to
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* collect 9 digits each (this is faster than using floating-point).
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* If the mantissa has more than 18 digits, ignore the extras, since
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* they can't affect the value anyway.
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*/
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pExp = p;
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p -= mantSize;
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if (decPt < 0) {
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decPt = mantSize;
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} else {
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mantSize -= 1; /* One of the digits was the point. */
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}
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if (mantSize > 18) {
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fracExp = decPt - 18;
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mantSize = 18;
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} else {
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fracExp = decPt - mantSize;
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}
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if (mantSize == 0) {
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fraction = 0.0;
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p = string;
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goto done;
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} else {
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int frac1, frac2;
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frac1 = 0;
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for ( ; mantSize > 9; mantSize -= 1)
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{
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c = *p;
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p += 1;
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if (c == '.') {
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c = *p;
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p += 1;
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}
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frac1 = 10*frac1 + (c - '0');
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}
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frac2 = 0;
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for (; mantSize > 0; mantSize -= 1)
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{
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c = *p;
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p += 1;
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if (c == '.') {
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c = *p;
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p += 1;
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}
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frac2 = 10*frac2 + (c - '0');
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}
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fraction = (1.0e9 * frac1) + frac2;
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}
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/*
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* Skim off the exponent.
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*/
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p = pExp;
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if ((*p == 'E') || (*p == 'e')) {
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p += 1;
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if (*p == '-') {
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expSign = 1;
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p += 1;
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} else {
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if (*p == '+') {
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p += 1;
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}
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expSign = 0;
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}
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while (isdigit(*p)) {
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exp = exp * 10 + (*p - '0');
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p += 1;
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}
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}
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if (expSign) {
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exp = fracExp - exp;
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} else {
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exp = fracExp + exp;
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}
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/*
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* Generate a floating-point number that represents the exponent.
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* Do this by processing the exponent one bit at a time to combine
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* many powers of 2 of 10. Then combine the exponent with the
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* fraction.
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*/
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if (exp < 0) {
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expSign = 1;
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exp = -exp;
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} else {
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expSign = 0;
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}
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if (exp > maxExponent) {
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exp = maxExponent;
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errno = ERANGE;
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}
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dblExp = 1.0;
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for (d = powersOf10; exp != 0; exp >>= 1, d += 1) {
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if (exp & 01) {
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dblExp *= *d;
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}
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}
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if (expSign) {
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fraction /= dblExp;
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} else {
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fraction *= dblExp;
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}
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done:
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if (endPtr != NULL) {
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*endPtr = (char *) p;
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}
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if (sign) {
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return -fraction;
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}
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return fraction;
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}
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