xref: /illumos-gate/usr/src/lib/libm/common/m9x/llround.c (revision 2bbdd445a21f9d61f4a0ca0faf05d5ceb2bd91f3)
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 __llround = llround
31 #if defined(__sparcv9) || defined(__amd64)
32 #pragma weak lround = llround
33 #pragma weak __lround = llround
34 #endif
35 
36 /*
37  * llround(x) rounds its argument to the nearest integer, rounding
38  * ties away from zero, and converts the result to a 64 bit signed
39  * integer.
40  *
41  * If x is NaN, infinite, or so large that the nearest integer
42  * would exceed 64 bits, the invalid operation exception is raised.
43  */
44 
45 #include "libm.h"
46 
47 long long
48 llround(double x) {
49 	union {
50 		unsigned i[2];
51 		double d;
52 	} xx;
53 	unsigned hx, sx, i;
54 
55 	xx.d = x;
56 	hx = xx.i[HIWORD] & ~0x80000000;
57 	sx = xx.i[HIWORD] & 0x80000000;
58 
59 	if (hx < 0x43300000) { /* |x| < 2^52 */
60 		/* handle |x| < 1 */
61 		if (hx < 0x3ff00000) {
62 			if (hx >= 0x3fe00000)
63 				return (sx ? -1LL : 1LL);
64 			return (0LL);
65 		}
66 
67 		/* round x at the integer bit */
68 		if (hx < 0x41300000) {
69 			i = 1 << (0x412 - (hx >> 20));
70 			xx.i[HIWORD] = (xx.i[HIWORD] + i) & ~(i | (i - 1));
71 			xx.i[LOWORD] = 0;
72 		} else {
73 			i = 1 << (0x432 - (hx >> 20));
74 			xx.i[LOWORD] += i;
75 			if (xx.i[LOWORD] < i)
76 				xx.i[HIWORD]++;
77 			xx.i[LOWORD] &= ~(i | (i - 1));
78 		}
79 	}
80 
81 	/* now x is nan, inf, or integral */
82 	return ((long long) xx.d);
83 }
84