first commit of the new libm!

[musl] / src / math / remainder.c

diff --git a/src/math/remainder.c b/src/math/remainder.c
new file mode 100644 (file)
index 0000000..db176c8
--- /dev/null
+++ b/src/math/remainder.c
@@ -0,0 +1,70 @@
+/* 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"
+
+static const double zero = 0.0;
+
+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 */
+               return (x*p)/(x*p);
+       if (hx >= 0x7ff00000 ||                              /* x not finite */
+           (hp >= 0x7ff00000 && (hp-0x7ff00000 | lp) != 0)) /* p is NaN */
+               // FIXME: why long double?
+               return ((long double)x*p)/((long double)x*p);
+
+       if (hp <= 0x7fdfffff)
+               x = fmod(x, p+p);  /* now x < 2p */
+       if (((hx-hp)|(lx-lp)) == 0)
+               return zero*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;
+}