xref: /illumos-gate/usr/src/lib/libm/common/m9x/round.c (revision ddc0e0b5)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 
22 /*
23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
24  */
25 /*
26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
27  * Use is subject to license terms.
28  */
29 
30 #pragma weak __round = round
31 
32 #include "libm.h"
33 
34 double
round(double x)35 round(double x) {
36 	union {
37 		unsigned i[2];
38 		double d;
39 	} xx;
40 	unsigned hx, sx, i;
41 
42 	xx.d = x;
43 	hx = xx.i[HIWORD] & ~0x80000000;
44 	sx = xx.i[HIWORD] & 0x80000000;
45 	if (hx < 0x43300000) {	/* |x| < 2^52 */
46 		if (hx < 0x3ff00000) {	/* |x| < 1 */
47 			if (hx >= 0x3fe00000)
48 				return (sx ? -1.0 : 1.0);
49 			return (sx ? -0.0 : 0.0);
50 		}
51 
52 		/* round x at the integer bit */
53 		if (hx < 0x41300000) {
54 			i = 1 << (0x412 - (hx >> 20));
55 			xx.i[HIWORD] = (xx.i[HIWORD] + i) & ~(i | (i - 1));
56 			xx.i[LOWORD] = 0;
57 		} else {
58 			i = 1 << (0x432 - (hx >> 20));
59 			xx.i[LOWORD] += i;
60 			if (xx.i[LOWORD] < i)
61 				xx.i[HIWORD]++;
62 			xx.i[LOWORD] &= ~(i | (i - 1));
63 		}
64 		return (xx.d);
65 	} else if (hx < 0x7ff00000)
66 		return (x);
67 	else
68 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
69 		return (hx >= 0x7ff80000 ? x : x + x);
70 		/* assumes sparc-like QNaN */
71 #else
72 		return (x + x);
73 #endif
74 }
75