5980be9b3c
This work is based in part on code from NetBSD libm, libc and kernel. The library is partly public domain and partly BSD-style licensed.
134 lines
3.3 KiB
C
134 lines
3.3 KiB
C
/* @(#)e_fmod.c 5.1 93/09/24 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include <sys/cdefs.h>
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#if defined(LIBM_SCCS) && !defined(lint)
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__RCSID("$NetBSD: e_fmod.c,v 1.11 2002/05/26 22:01:49 wiz Exp $");
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#endif
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/*
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* __ieee754_fmod(x,y)
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* Return x mod y in exact arithmetic
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* Method: shift and subtract
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*/
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#include "math.h"
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#include "math_private.h"
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static const double one = 1.0, Zero[] = {0.0, -0.0,};
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double
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__ieee754_fmod(double x, double y)
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{
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int32_t n,hx,hy,hz,ix,iy,sx,i;
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uint32_t lx,ly,lz;
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EXTRACT_WORDS(hx,lx,x);
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EXTRACT_WORDS(hy,ly,y);
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sx = hx&0x80000000; /* sign of x */
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hx ^=sx; /* |x| */
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hy &= 0x7fffffff; /* |y| */
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/* purge off exception values */
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if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
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((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
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return (x*y)/(x*y);
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if(hx<=hy) {
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if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
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if(lx==ly)
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return Zero[(uint32_t)sx>>31]; /* |x|=|y| return x*0*/
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}
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/* determine ix = ilogb(x) */
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if(hx<0x00100000) { /* subnormal x */
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if(hx==0) {
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for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
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} else {
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for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
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}
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} else ix = (hx>>20)-1023;
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/* determine iy = ilogb(y) */
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if(hy<0x00100000) { /* subnormal y */
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if(hy==0) {
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for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
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} else {
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for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
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}
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} else iy = (hy>>20)-1023;
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/* set up {hx,lx}, {hy,ly} and align y to x */
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if(ix >= -1022)
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hx = 0x00100000|(0x000fffff&hx);
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else { /* subnormal x, shift x to normal */
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n = -1022-ix;
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if(n<=31) {
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hx = (hx<<n)|(lx>>(32-n));
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lx <<= n;
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} else {
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hx = lx<<(n-32);
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lx = 0;
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}
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}
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if(iy >= -1022)
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hy = 0x00100000|(0x000fffff&hy);
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else { /* subnormal y, shift y to normal */
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n = -1022-iy;
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if(n<=31) {
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hy = (hy<<n)|(ly>>(32-n));
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ly <<= n;
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} else {
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hy = ly<<(n-32);
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ly = 0;
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}
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}
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/* fix point fmod */
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n = ix - iy;
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while(n--) {
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hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
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if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
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else {
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if((hz|lz)==0) /* return sign(x)*0 */
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return Zero[(uint32_t)sx>>31];
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hx = hz+hz+(lz>>31); lx = lz+lz;
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}
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}
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hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
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if(hz>=0) {hx=hz;lx=lz;}
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/* convert back to floating value and restore the sign */
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if((hx|lx)==0) /* return sign(x)*0 */
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return Zero[(uint32_t)sx>>31];
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while(hx<0x00100000) { /* normalize x */
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hx = hx+hx+(lx>>31); lx = lx+lx;
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iy -= 1;
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}
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if(iy>= -1022) { /* normalize output */
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hx = ((hx-0x00100000)|((iy+1023)<<20));
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INSERT_WORDS(x,hx|sx,lx);
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} else { /* subnormal output */
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n = -1022 - iy;
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if(n<=20) {
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lx = (lx>>n)|((uint32_t)hx<<(32-n));
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hx >>= n;
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} else if (n<=31) {
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lx = (hx<<(32-n))|(lx>>n); hx = sx;
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} else {
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lx = hx>>(n-32); hx = sx;
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}
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INSERT_WORDS(x,hx|sx,lx);
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x *= one; /* create necessary signal */
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}
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return x; /* exact output */
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}
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