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Diffstat (limited to 'compat/strtod.c')
| -rw-r--r-- | compat/strtod.c | 252 |
1 files changed, 252 insertions, 0 deletions
diff --git a/compat/strtod.c b/compat/strtod.c new file mode 100644 index 0000000..9643c09 --- /dev/null +++ b/compat/strtod.c @@ -0,0 +1,252 @@ +/* + * 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. + */ + +#include "tclInt.h" + +#ifndef TRUE +#define TRUE 1 +#define FALSE 0 +#endif +#ifndef NULL +#define NULL 0 +#endif + +static const 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 const 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( + 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; + const double *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) { + 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; +} |