first commit of the new libm!

[musl] / src / math / fmod.c

diff --git a/src/math/fmod.c b/src/math/fmod.c
new file mode 100644 (file)
index 0000000..6856844
--- /dev/null
+++ b/src/math/fmod.c
@@ -0,0 +1,146 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/e_fmod.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.
+ * ====================================================
+ */
+/*
+ * fmod(x,y)
+ * Return x mod y in exact arithmetic
+ * Method: shift and subtract
+ */
+
+#include "libm.h"
+
+static const double one = 1.0, Zero[] = {0.0, -0.0,};
+
+double fmod(double x, double y)
+{
+       int32_t n,hx,hy,hz,ix,iy,sx,i;
+       uint32_t lx,ly,lz;
+
+       EXTRACT_WORDS(hx, lx, x);
+       EXTRACT_WORDS(hy, ly, y);
+       sx = hx & 0x80000000;  /* sign of x */
+       hx ^= sx;              /* |x| */
+       hy &= 0x7fffffff;      /* |y| */
+
+       /* purge off exception values */
+       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;
+               if (lx == ly)            /* |x| = |y|, return x*0 */
+                       return Zero[(uint32_t)sx>>31];
+       }
+
+       /* determine ix = ilogb(x) */
+       if (hx < 0x00100000) {  /* subnormal x */
+               if (hx == 0) {
+                       for (ix = -1043, i = lx; i > 0; i <<= 1)
+                               ix -= 1;
+               } else {
+                       for (ix = -1022, i = hx<<11; i > 0; i <<= 1)
+                               ix -= 1;
+               }
+       } 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 -= 1;
+               } else {
+                       for (iy = -1022, i = hy<<11; i > 0; i <<= 1)
+                               iy -= 1;
+               }
+       } 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;
+       while (n--) {
+               hz = hx-hy;
+               lz = lx-ly;
+               if (lx < ly)
+                       hz -= 1;
+               if (hz < 0) {
+                       hx = hx+hx+(lx>>31);
+                       lx = lx+lx;
+               } else {
+                       if ((hz|lz) == 0)   /* return sign(x)*0 */
+                               return Zero[(uint32_t)sx>>31];
+                       hx = hz+hz+(lz>>31);
+                       lx = lz+lz;
+               }
+       }
+       hz = hx-hy;
+       lz = lx-ly;
+       if (lx < ly)
+               hz -= 1;
+       if (hz >= 0) {
+               hx = hz;
+               lx = lz;
+       }
+
+       /* convert back to floating value and restore the sign */
+       if ((hx|lx) == 0)          /* return sign(x)*0 */
+               return Zero[(uint32_t)sx>>31];
+       while (hx < 0x00100000) {  /* normalize x */
+               hx = hx+hx+(lx>>31);
+               lx = lx+lx;
+               iy -= 1;
+       }
+       if (iy >= -1022) {         /* normalize output */
+               hx = ((hx-0x00100000)|((iy+1023)<<20));
+               INSERT_WORDS(x, hx|sx, lx);
+       } 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;
+               }
+               INSERT_WORDS(x, hx|sx, lx);
+               x *= one;  /* create necessary signal */
+       }
+       return x;  /* exact output */
+}