/************************************************************************
*									*
*	The SB-Prolog System						*
*	Copyright SUNY at Stony Brook, 1986				*
*									*
************************************************************************/

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unless he says so in writing.  Refer to the SB-Prolog General Public
License for full details.

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SB-Prolog, but only under the conditions described in the
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supposed to have been given to you along with SB-Prolog so you
can know your rights and responsibilities.  It should be in a
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------------------------------------------------------------------ */

#ifndef	lint
static	char	rcsid[] = "$Header: float.c 1.2 87/10/24 $";
#endif

/*
 * float.c
 *
 * WAM representation of floats: bits 0-2: tag (010); bits 3-7: absolute
 * value of exponent; bits 8-29: absolute value of mantissa; bit 30:
 * sign of exponent (1: negative); bit 31: sign of mantissa (1: negative).
 */

/* $Log:	float.c,v $
 * Revision 1.2  87/10/24  14:55:03  rbk
 * Fix prettymuch_equal() to unify floating zero with only floating zero;
 * previous version would dump core with floating-point zero-divide.
 * This is a minor (but reasonable) semantic change.
 * 
 */

#include "sim.h"
#include "aux.h"

#define Bit21	    0x200000
#define EXP_SIGN    0x40000000
#define MANT_SIGN   0x80000000
#define exp_magn(op)    (((unsigned)(op & 0xff)) >> 3)
#define mant_magn(op)	(((unsigned)(op & 0x3fffff00)) >> 8)

double frexp(), ldexp();	/* C library routines */

/* "floatval" converts floats from the WAM representation to the machine
   representation.							*/

double floatval(op)
word op;
{
    register long exponent, exp_sign;
    double fval; int exp;

    exp_sign = op & EXP_SIGN;
    fval = (double)mant_magn(op); exponent = exp_magn(op);
    if (exp_sign) exp = -exponent; else exp = exponent;
    if (op & MANT_SIGN) fval = -fval;
    return ldexp(fval, exp);
}

/* "makefloat" converts floats from the machine representation to the WAM
   representation.							  */

word makefloat(op)
double op;
{
    long exp_sign, mant_sign;
    int exponent;

    if (op < 0) {
	mant_sign = MANT_SIGN;
	op = -op;}
    else mant_sign = 0;
    op = frexp(op, &exponent);
    if ((op == 0.0) || (exponent <= -32)) {op = 0.0; exponent = 0;}
    else
    {	while ( !(((int)op)&Bit21) && (exponent > -31))  /* keep top 10 bits */
	{   op *= 2;				         /* clear for shifting */
	    exponent -= 1;
	};
    };
    if (exponent < 0) {
	exponent = -exponent;
	exp_sign = EXP_SIGN;
    } else exp_sign = 0;
    return ( ((word)op<<8) | (exponent<<3) | exp_sign | mant_sign | FLOAT_TAG);
}

prettymuch_equal(op1, op2)
double op1, op2;
{
    double min, diff;

    if (op1<0) op1 = -op1;
    if (op2<0) op2 = -op2;
    if (op1 < op2) min = op1; else min = op2;
    if (min == 0.0) return(op1 == op2);	/* if one is zero, insist both be */
    diff = op1 - op2; if (diff < 0) diff = -diff;
    return ( (diff/min) < EPSILON);
}