/* 

 * 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 1.6 2002/02/25 14:26:12 dgp Exp $

 */

#include "tclInt.h"

#include "tclPort.h"

#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(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 += 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;

}