/* 

  * 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;

 }