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/*

 * 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 1.1.1.1 2002-01-16 10:25:23 markom Exp $

 */

#include "tcl.h"

#ifdef NO_STDLIB_H

#   include "../compat/stdlib.h"

#else

#   include <stdlib.h>

#endif

#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(*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;

        }

        while (isdigit(*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;

    }

    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;

}