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authorRich Felker <dalias@aerifal.cx>2011-02-12 00:22:29 -0500
committerRich Felker <dalias@aerifal.cx>2011-02-12 00:22:29 -0500
commit0b44a0315b47dd8eced9f3b7f31580cf14bbfc01 (patch)
tree6eaef0d8a720fa3da580de87b647fff796fe80b3 /src/math/s_remquof.c
downloadmusl-0b44a0315b47dd8eced9f3b7f31580cf14bbfc01.tar.gz
initial check-in, version 0.5.0v0.5.0
Diffstat (limited to 'src/math/s_remquof.c')
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1 files changed, 118 insertions, 0 deletions
diff --git a/src/math/s_remquof.c b/src/math/s_remquof.c
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+/* @(#)e_fmod.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.
+ * ====================================================
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+static const float Zero[] = {0.0, -0.0,};
+
+/*
+ * Return the IEEE remainder and set *quo to the last n bits of the
+ * quotient, rounded to the nearest integer. We choose n=31 because
+ * we wind up computing all the integer bits of the quotient anyway as
+ * a side-effect of computing the remainder by the shift and subtract
+ * method. In practice, this is far more bits than are needed to use
+ * remquo in reduction algorithms.
+ */
+float
+remquof(float x, float y, int *quo)
+{
+ int32_t n,hx,hy,hz,ix,iy,sx,i;
+ uint32_t q,sxy;
+
+ GET_FLOAT_WORD(hx,x);
+ GET_FLOAT_WORD(hy,y);
+ sxy = (hx ^ hy) & 0x80000000;
+ sx = hx&0x80000000; /* sign of x */
+ hx ^=sx; /* |x| */
+ hy &= 0x7fffffff; /* |y| */
+
+ /* purge off exception values */
+ if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
+ return (x*y)/(x*y);
+ if(hx<hy) {
+ q = 0;
+ goto fixup; /* |x|<|y| return x or x-y */
+ } else if(hx==hy) {
+ *quo = 1;
+ return Zero[(uint32_t)sx>>31]; /* |x|=|y| return x*0*/
+ }
+
+ /* determine ix = ilogb(x) */
+ if(hx<0x00800000) { /* subnormal x */
+ for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
+ } else ix = (hx>>23)-127;
+
+ /* determine iy = ilogb(y) */
+ if(hy<0x00800000) { /* subnormal y */
+ for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
+ } else iy = (hy>>23)-127;
+
+ /* set up {hx,lx}, {hy,ly} and align y to x */
+ if(ix >= -126)
+ hx = 0x00800000|(0x007fffff&hx);
+ else { /* subnormal x, shift x to normal */
+ n = -126-ix;
+ hx <<= n;
+ }
+ if(iy >= -126)
+ hy = 0x00800000|(0x007fffff&hy);
+ else { /* subnormal y, shift y to normal */
+ n = -126-iy;
+ hy <<= n;
+ }
+
+ /* fix point fmod */
+ n = ix - iy;
+ q = 0;
+ while(n--) {
+ hz=hx-hy;
+ if(hz<0) hx = hx << 1;
+ else {hx = hz << 1; q++;}
+ q <<= 1;
+ }
+ hz=hx-hy;
+ if(hz>=0) {hx=hz;q++;}
+
+ /* convert back to floating value and restore the sign */
+ if(hx==0) { /* return sign(x)*0 */
+ *quo = (sxy ? -q : q);
+ return Zero[(uint32_t)sx>>31];
+ }
+ while(hx<0x00800000) { /* normalize x */
+ hx <<= 1;
+ iy -= 1;
+ }
+ if(iy>= -126) { /* normalize output */
+ hx = ((hx-0x00800000)|((iy+127)<<23));
+ } else { /* subnormal output */
+ n = -126 - iy;
+ hx >>= n;
+ }
+fixup:
+ SET_FLOAT_WORD(x,hx);
+ y = fabsf(y);
+ if (y < 0x1p-125f) {
+ if (x+x>y || (x+x==y && (q & 1))) {
+ q++;
+ x-=y;
+ }
+ } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
+ q++;
+ x-=y;
+ }
+ GET_FLOAT_WORD(hx,x);
+ SET_FLOAT_WORD(x,hx^sx);
+ q &= 0x7fffffff;
+ *quo = (sxy ? -q : q);
+ return x;
+}