first commit of the new libm!

[musl] / src / math / rint.c

diff --git a/src/math/rint.c b/src/math/rint.c
new file mode 100644 (file)
index 0000000..775c7b8
--- /dev/null
+++ b/src/math/rint.c
@@ -0,0 +1,90 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/s_rint.c */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+/*
+ * rint(x)
+ * Return x rounded to integral value according to the prevailing
+ * rounding mode.
+ * Method:
+ *      Using floating addition.
+ * Exception:
+ *      Inexact flag raised if x not equal to rint(x).
+ */
+
+#include "libm.h"
+
+static const double
+TWO52[2] = {
+  4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
+ -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
+};
+
+double rint(double x)
+{
+       int32_t i0,j0,sx;
+       uint32_t i,i1;
+       double w,t;
+
+       EXTRACT_WORDS(i0, i1, x);
+       // FIXME: signed shift
+       sx = (i0>>31) & 1;
+       j0 = ((i0>>20)&0x7ff) - 0x3ff;
+       if (j0 < 20) {
+               if (j0 < 0) {
+                       if (((i0&0x7fffffff)|i1) == 0)
+                               return x;
+                       i1 |= i0 & 0x0fffff;
+                       i0 &= 0xfffe0000;
+                       i0 |= ((i1|-i1)>>12) & 0x80000;
+                       SET_HIGH_WORD(x, i0);
+                       STRICT_ASSIGN(double, w, TWO52[sx] + x);
+                       t = w - TWO52[sx];
+                       GET_HIGH_WORD(i0, t);
+                       SET_HIGH_WORD(t, (i0&0x7fffffff)|(sx<<31));
+                       return t;
+               } else {
+                       i = 0x000fffff>>j0;
+                       if (((i0&i)|i1) == 0)
+                               return x; /* x is integral */
+                       i >>= 1;
+                       if (((i0&i)|i1) != 0) {
+                               /*
+                                * Some bit is set after the 0.5 bit.  To avoid the
+                                * possibility of errors from double rounding in
+                                * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
+                                * guard bit.  We do this for all j0<=51.  The
+                                * adjustment is trickiest for j0==18 and j0==19
+                                * since then it spans the word boundary.
+                                */
+                               if (j0 == 19)
+                                       i1 = 0x40000000;
+                               else if (j0 == 18)
+                                       i1 = 0x80000000;
+                               else
+                                       i0 = (i0 & ~i)|(0x20000>>j0);
+                       }
+               }
+       } else if (j0 > 51) {
+               if (j0 == 0x400)
+                       return x+x;  /* inf or NaN */
+               return x;            /* x is integral */
+       } else {
+               i = (uint32_t)0xffffffff>>(j0-20);
+               if ((i1&i) == 0)
+                       return x;    /* x is integral */
+               i >>= 1;
+               if ((i1&i) != 0)
+                       i1 = (i1 & ~i)|(0x40000000>>(j0-20));
+       }
+       INSERT_WORDS(x, i0, i1);
+       STRICT_ASSIGN(double, w, TWO52[sx] + x);
+       return w - TWO52[sx];
+}