math: rewrite rounding functions (ceil, floor, trunc, round, rint)

* faster, smaller, cleaner implementation than the bit hacks of fdlibm
* use arithmetics like y=(double)(x+0x1p52)-0x1p52, which is an integer
neighbor of x in all rounding modes (0<=x<0x1p52) and only use bithacks
when that's faster and smaller (for float it usually is)
* the code assumes standard excess precision handling for casts
* long double code supports both ld80 and ld128
* nearbyint is not changed (it is a wrapper around rint)

1 files changed, 19 insertions, 56 deletions

diff --git a/src/math/floorf.c b/src/math/floorf.c
index 23fa5e7d..dceec739 100644
--- a/src/math/floorf.c
+++ b/src/math/floorf.c
@@ -1,64 +1,27 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/s_floorf.c */
-/*
- * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
- */
-/*
- * ====================================================
- * 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.
- * ====================================================
- */
-/*
- * floorf(x)
- * Return x rounded toward -inf to integral value
- * Method:
- *      Bit twiddling.
- * Exception:
- *      Inexact flag raised if x not equal to floorf(x).
- */
-
 #include "libm.h"
 
-static const float huge = 1.0e30;
-
 float floorf(float x)
 {
-	int32_t i0,j0;
-	uint32_t i;
+	union {float f; uint32_t i;} u = {x};
+	int e = (int)(u.i >> 23 & 0xff) - 0x7f;
+	uint32_t m;
 
-	GET_FLOAT_WORD(i0, x);
-	// FIXME: signed shift
-	j0 = ((i0>>23)&0xff) - 0x7f;
-	if (j0 < 23) {
-		if (j0 < 0) {  /* |x| < 1 */
-			/* raise inexact if x != 0 */
-			if (huge+x > 0.0f) {
-				if (i0 >= 0)  /* x >= 0 */
-					i0 = 0;
-				else if ((i0&0x7fffffff) != 0)
-					i0 = 0xbf800000;
-			}
-		} else {
-			i = 0x007fffff>>j0;
-			if ((i0&i) == 0)
-				return x; /* x is integral */
-			/* raise inexact flag */
-			if (huge+x > 0.0f) {
-				if (i0 < 0)
-					i0 += 0x00800000>>j0;
-				i0 &= ~i;
-			}
-		}
+	if (e >= 23)
+		return x;
+	if (e >= 0) {
+		m = 0x007fffff >> e;
+		if ((u.i & m) == 0)
+			return x;
+		FORCE_EVAL(x + 0x1p120f);
+		if (u.i >> 31)
+			u.i += m;
+		u.i &= ~m;
 	} else {
-		if (j0 == 0x80)  /* inf or NaN */
-			return x+x;
-		else
-			return x;  /* x is integral */
+		FORCE_EVAL(x + 0x1p120f);
+		if (u.i >> 31 == 0)
+			u.i = 0;
+		else if (u.i << 1)
+			u.f = -1.0;
 	}
-	SET_FLOAT_WORD(x, i0);
-	return x;
+	return u.f;
 }