xref: /illumos-gate/usr/src/lib/libm/common/m9x/llrintf.c (revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8)
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 llrintf = __llrintf
32 #if defined(__sparcv9) || defined(__amd64)
33 #pragma weak lrintf = __llrintf
34 #pragma weak __lrintf = __llrintf
35 #endif
36 #endif
37 
38 #include "libm.h"
39 
40 long long
41 llrintf(float x) {
42 	/*
43 	 * Note: The following code works on x86 (in the default rounding
44 	 * precision mode), but one should just use the fistpll instruction
45 	 * instead.
46 	 */
47 	union {
48 		unsigned i;
49 		float f;
50 	} xx, yy;
51 	unsigned hx;
52 
53 	xx.f = x;
54 	hx = xx.i & ~0x80000000;
55 
56 	if (hx < 0x4b000000) { /* |x| < 2^23 */
57 		/* add and subtract a power of two to round x to an integer */
58 #if defined(__sparc) || defined(__amd64)
59 		yy.i = (xx.i & 0x80000000) | 0x4b000000;
60 #elif defined(__i386)
61 		/* assume 64-bit precision */
62 		yy.i = (xx.i & 0x80000000) | 0x5f000000;
63 #else
64 #error Unknown architecture
65 #endif
66 		x = (x + yy.f) - yy.f;
67 
68 		/*
69 		 * on LP32 architectures, we can just convert x to a 32-bit
70 		 * integer and sign-extend it
71 		 */
72 		return ((long) x);
73 	}
74 
75 	/* now x is nan, inf, or integral */
76 	return ((long long) x);
77 }
78