--- /dev/null
+/* origin: FreeBSD /usr/src/lib/msun/src/s_remquo.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.
+ * ====================================================
+ */
+/*
+ * 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.
+ */
+
+#include "libm.h"
+
+static const double Zero[] = {0.0, -0.0,};
+
+double remquo(double x, double y, int *quo)
+{
+ int32_t n,hx,hy,hz,ix,iy,sx,i;
+ uint32_t lx,ly,lz,q,sxy;
+
+ EXTRACT_WORDS(hx, lx, x);
+ EXTRACT_WORDS(hy, ly, y);
+ sxy = (hx ^ hy) & 0x80000000;
+ sx = hx & 0x80000000; /* sign of x */
+ hx ^= sx; /* |x| */
+ hy &= 0x7fffffff; /* |y| */
+
+ /* purge off exception values */
+ // FIXME: signed shift
+ if ((hy|ly) == 0 || hx >= 0x7ff00000 || /* y = 0, or x not finite */
+ (hy|((ly|-ly)>>31)) > 0x7ff00000) /* or y is NaN */
+ return (x*y)/(x*y);
+ if (hx <= hy) {
+ if (hx < hy || lx < ly) { /* |x| < |y| return x or x-y */
+ q = 0;
+ goto fixup;
+ }
+ if (lx == ly) { /* |x| = |y| return x*0 */
+ *quo = 1;
+ return Zero[(uint32_t)sx>>31];
+ }
+ }
+
+ // FIXME: use ilogb?
+
+ /* determine ix = ilogb(x) */
+ if (hx < 0x00100000) { /* subnormal x */
+ if (hx == 0) {
+ for (ix = -1043, i=lx; i>0; i<<=1) ix--;
+ } else {
+ for (ix = -1022, i=hx<<11; i>0; i<<=1) ix--;
+ }
+ } else
+ ix = (hx>>20) - 1023;
+
+ /* determine iy = ilogb(y) */
+ if (hy < 0x00100000) { /* subnormal y */
+ if (hy == 0) {
+ for (iy = -1043, i=ly; i>0; i<<=1) iy--;
+ } else {
+ for (iy = -1022, i=hy<<11; i>0; i<<=1) iy--;
+ }
+ } else
+ iy = (hy>>20) - 1023;
+
+ /* set up {hx,lx}, {hy,ly} and align y to x */
+ if (ix >= -1022)
+ hx = 0x00100000|(0x000fffff&hx);
+ else { /* subnormal x, shift x to normal */
+ n = -1022 - ix;
+ if (n <= 31) {
+ hx = (hx<<n)|(lx>>(32-n));
+ lx <<= n;
+ } else {
+ hx = lx<<(n-32);
+ lx = 0;
+ }
+ }
+ if (iy >= -1022)
+ hy = 0x00100000|(0x000fffff&hy);
+ else { /* subnormal y, shift y to normal */
+ n = -1022 - iy;
+ if (n <= 31) {
+ hy = (hy<<n)|(ly>>(32-n));
+ ly <<= n;
+ } else {
+ hy = ly<<(n-32);
+ ly = 0;
+ }
+ }
+
+ /* fix point fmod */
+ n = ix - iy;
+ q = 0;
+ while (n--) {
+ hz = hx - hy;
+ lz = lx - ly;
+ if (lx < ly)
+ hz--;
+ if (hz < 0) {
+ hx = hx + hx + (lx>>31);
+ lx = lx + lx;
+ } else {
+ hx = hz + hz + (lz>>31);
+ lx = lz + lz;
+ q++;
+ }
+ q <<= 1;
+ }
+ hz = hx - hy;
+ lz = lx - ly;
+ if (lx < ly)
+ hz--;
+ if (hz >= 0) {
+ hx = hz;
+ lx = lz;
+ q++;
+ }
+
+ /* convert back to floating value and restore the sign */
+ if ((hx|lx) == 0) { /* return sign(x)*0 */
+ *quo = sxy ? -q : q;
+ return Zero[(uint32_t)sx>>31];
+ }
+ while (hx < 0x00100000) { /* normalize x */
+ hx = hx + hx + (lx>>31);
+ lx = lx + lx;
+ iy--;
+ }
+ if (iy >= -1022) { /* normalize output */
+ hx = (hx-0x00100000)|((iy+1023)<<20);
+ } else { /* subnormal output */
+ n = -1022 - iy;
+ if (n <= 20) {
+ lx = (lx>>n)|((uint32_t)hx<<(32-n));
+ hx >>= n;
+ } else if (n <= 31) {
+ lx = (hx<<(32-n))|(lx>>n);
+ hx = sx;
+ } else {
+ lx = hx>>(n-32);
+ hx = sx;
+ }
+ }
+fixup:
+ INSERT_WORDS(x, hx, lx);
+ y = fabs(y);
+ if (y < 0x1p-1021) {
+ if (x + x > y || (x + x == y && (q & 1))) {
+ q++;
+ x -= y;
+ }
+ } else if (x > 0.5*y || (x == 0.5*y && (q & 1))) {
+ q++;
+ x -= y;
+ }
+ GET_HIGH_WORD(hx, x);
+ SET_HIGH_WORD(x, hx ^ sx);
+ q &= 0x7fffffff;
+ *quo = sxy ? -q : q;
+ return x;
+}
projects / musl / blobdiff