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, 20 insertions, 41 deletions

diff --git a/src/math/roundf.c b/src/math/roundf.c
index 662a454b..c6b27797 100644
--- a/src/math/roundf.c
+++ b/src/math/roundf.c
@@ -1,48 +1,27 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/s_roundf.c */
-/*-
- * Copyright (c) 2003, Steven G. Kargl
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice unmodified, this list of conditions, and the following
- *    disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
- * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
- * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
- * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
- * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
- * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
- * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
- * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
- * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#include <math.h>
+#include "libm.h"
 
 float roundf(float x)
 {
-	float t;
+	union {float f; uint32_t i;} u = {x};
+	int e = u.i >> 23 & 0xff;
+	float_t y;
 
-	if (!isfinite(x))
+	if (e >= 0x7f+23)
 		return x;
-
-	if (x >= 0.0) {
-		t = floorf(x);
-		if (t - x <= -0.5)
-			t += 1.0;
-		return t;
-	} else {
-		t = floorf(-x);
-		if (t + x <= -0.5)
-			t += 1.0;
-		return -t;
+	if (u.i >> 31)
+		x = -x;
+	if (e < 0x7f-1) {
+		FORCE_EVAL(x + 0x1p23f);
+		return 0*u.f;
 	}
+	y = (float)(x + 0x1p23f) - 0x1p23f - x;
+	if (y > 0.5f)
+		y = y + x - 1;
+	else if (y <= -0.5f)
+		y = y + x + 1;
+	else
+		y = y + x;
+	if (u.i >> 31)
+		y = -y;
+	return y;
 }