xref: /titanic_50/usr/src/lib/libm/common/m9x/llrint.c (revision 89621fe174cf95ae903df6ceab605bf24d696ac3)
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 #if defined(ELFOBJ)
31 #pragma weak llrint = __llrint
32 #if defined(__sparcv9) || defined(__amd64)
33 #pragma weak lrint = __llrint
34 #pragma weak __lrint = __llrint
35 #endif
36 #endif
37 
38 /*
39  * llrint(x) rounds its argument to the nearest integer according
40  * to the current rounding direction and converts the result to a
41  * 64 bit signed integer.
42  *
43  * If x is NaN, infinite, or so large that the nearest integer would
44  * exceed 64 bits, the invalid operation exception is raised.  If x
45  * is not an integer, the inexact exception is raised.
46  */
47 
48 #include "libm.h"
49 
50 long long
51 llrint(double x) {
52 	/*
53 	 * Note: The following code works on x86 (in the default rounding
54 	 * precision mode), but one should just use the fistpll instruction
55 	 * instead.
56 	 */
57 	union {
58 		unsigned i[2];
59 		double d;
60 	} xx, yy;
61 	unsigned hx;
62 
63 	xx.d = x;
64 	hx = xx.i[HIWORD] & ~0x80000000;
65 
66 	if (hx < 0x43300000) { /* |x| < 2^52 */
67 		/* add and subtract a power of two to round x to an integer */
68 #if defined(__sparc) || defined(__amd64)
69 		yy.i[HIWORD] = (xx.i[HIWORD] & 0x80000000) | 0x43300000;
70 #elif defined(__i386)	/* !defined(__amd64) */
71 		yy.i[HIWORD] = (xx.i[HIWORD] & 0x80000000) | 0x43e00000;
72 #else
73 #error Unknown architecture
74 #endif
75 		yy.i[LOWORD] = 0;
76 		x = (x + yy.d) - yy.d;
77 	}
78 
79 	/* now x is nan, inf, or integral */
80 	return ((long long) x);
81 }
82