e_remainder.c

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/* @(#)e_remainder.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/* __ieee754_remainder(x,p)
 * Return :                  
 *  returns  x REM p  =  x - [x/p]*p as if in infinite 
 *  precise arithmetic, where [x/p] is the (infinite bit) 
 *  integer nearest x/p (in half way case choose the even one).
 * Method : 
 *  Based on fmod() return x-[x/p]chopped*p exactlp.
 */

#include "fdlibm.h"

#ifdef __STDC__
static const double zero = 0.0;
#else
static double zero = 0.0;
#endif


#ifdef __STDC__
    double __ieee754_remainder(double x, double p)
#else
    double __ieee754_remainder(x,p)
    double x,p;
#endif
{
    int hx,hp;
    unsigned sx,lx,lp;
    double p_half;

    hx = __HI(x);       /* high word of x */
    lx = __LO(x);       /* low  word of x */
    hp = __HI(p);       /* high word of p */
    lp = __LO(p);       /* low  word of p */
    sx = hx&0x80000000;
    hp &= 0x7fffffff;
    hx &= 0x7fffffff;

    /* purge off exception values */
    if((hp|lp)==0) return (x*p)/(x*p);  /* p = 0 */
    if((hx>=0x7ff00000)||           /* x not finite */
      ((hp>=0x7ff00000)&&           /* p is NaN */
      (((hp-0x7ff00000)|lp)!=0)))
        return (x*p)/(x*p);


    if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p);  /* now x < 2p */
    if (((hx-hp)|(lx-lp))==0) return zero*x;
    x  = fabs(x);
    p  = fabs(p);
    if (hp<0x00200000) {
        if(x+x>p) {
        x-=p;
        if(x+x>=p) x -= p;
        }
    } else {
        p_half = 0.5*p;
        if(x>p_half) {
        x-=p;
        if(x>=p_half) x -= p;
        }
    }
    __HI(x) ^= sx;
    return x;
}