musl/src/math/remainder.c

/* origin: FreeBSD /usr/src/lib/msun/src/e_remainder.c */
/*
 * ====================================================
 * 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.
 * ====================================================
 */
/* 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 "libm.h"

double remainder(double x, double p)
{
	int32_t hx,hp;
	uint32_t sx,lx,lp;
	double p_half;

	EXTRACT_WORDS(hx, lx, x);
	EXTRACT_WORDS(hp, lp, p);
	sx = hx & 0x80000000;
	hp &= 0x7fffffff;
	hx &= 0x7fffffff;

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

	if (hp <= 0x7fdfffff)
		x = fmod(x, p+p);  /* now x < 2p */
	if (((hx-hp)|(lx-lp)) == 0)
		return 0.0*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;
		}
	}
	GET_HIGH_WORD(hx, x);
	if ((hx&0x7fffffff) == 0)
		hx = 0;
	SET_HIGH_WORD(x, hx^sx);
	return x;
}