xref: /illumos-gate/usr/src/lib/libm/common/C/rint.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  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
23  */
24 /*
25  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
26  * Use is subject to license terms.
27  */
28 
29 #pragma weak __rint = rint
30 
31 /*
32  * rint(x) return x rounded to integral according to the rounding direction
33  * rint(x) returns result with the same sign as x's,  including 0.0.
34  */
35 
36 #include "libm.h"
37 
38 #if defined(__i386) && !defined(__amd64) && (!defined(__FLT_EVAL_METHOD__) || \
39 	__FLT_EVAL_METHOD__ != 0)
40 extern enum fp_precision_type __swapRP(enum fp_precision_type);
41 #define	DECLRP(x)	enum fp_precision_type x;
42 #define	SWAPRP(new, x)	x = __swapRP(new);
43 #define	RESTRP(x)	(void) __swapRP(x);
44 #else
45 #define	DECLRP(x)
46 #define	SWAPRP(new, x)
47 #define	RESTRP(x)
48 #endif
49 
50 static const double
51 	two52 = 4503599627370496.0,
52 	zero = 0.0,
53 	one = 1.0;
54 
55 double
rint(double x)56 rint(double x) {
57 	DECLRP(rp)
58 	double	t, w;
59 	int	ix, hx;
60 
61 	ix = ((int *)&x)[HIWORD];
62 	hx = ix & ~0x80000000;
63 
64 	if (hx >= 0x43300000)
65 		return (x * one);
66 	t = (ix < 0)? -two52 : two52;
67 	SWAPRP(fp_double, rp)		/* set precision mode to double */
68 	w = x + t;			/* x+sign(x)*2**52 rounded */
69 	RESTRP(rp)			/* restore precision mode */
70 	if (w == t)
71 		return ((ix < 0)? -zero : zero);
72 	return (w - t);
73 }
74