xref: /titanic_41/usr/src/lib/libm/common/Q/scalbnl.c (revision a9d3dcd5820128b4f34bf38f447e47aa95c004e8)
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 __scalbnl = scalbnl
31 
32 #include "libm.h"
33 #include <float.h>		/* LDBL_MAX, LDBL_MIN */
34 #include <stdlib.h>		/* abs */
35 
36 #if defined(__sparc)
37 #define	XSET_EXP(k, x)	((int *) &x)[0] = (((int *) &x)[0] & ~0x7fff0000) | \
38 				(k << 16)
39 #define	ISINFNANL(k, x)	(k == 0x7fff)
40 #define	XTWOT_OFFSET	113
41 static const long double xtwot = 10384593717069655257060992658440192.0L,
42 								/* 2^113 */
43 	twomtm1 = 4.814824860968089632639944856462318296E-35L;	/* 2^-114 */
44 #elif defined(__x86)
45 #define	XSET_EXP(k, x)	((int *) &x)[2] = (((int *) &x)[2] & ~0x7fff) | k
46 #if defined(HANDLE_UNSUPPORTED)
47 #define	ISINFNANL(k, x)	(k == 0x7fff || k != 0 && \
48 				(((int *) &x)[1] & 0x80000000) == 0)
49 #else
50 #define	ISINFNANL(k, x)	(k == 0x7fff)
51 #endif
52 #define	XTWOT_OFFSET	64
53 static const long double xtwot = 18446744073709551616.0L,	/* 2^64 */
54 	twomtm1 = 2.7105054312137610850186E-20L;		/* 2^-65 */
55 #endif
56 
57 long double
scalbnl(long double x,int n)58 scalbnl(long double x, int n) {
59 	int k = XBIASED_EXP(x);
60 
61 	if (ISINFNANL(k, x))
62 		return (x + x);
63 	if (ISZEROL(x) || n == 0)
64 		return (x);
65 	if (k == 0) {
66 		x *= xtwot;
67 		k = XBIASED_EXP(x) - XTWOT_OFFSET;
68 	}
69 	if ((unsigned) abs(n) >= 131072)	/* cast to unsigned for -2^31 */
70 		n >>= 1;		/* avoid subsequent integer overflow */
71 	k += n;
72 	if (k > 0x7ffe)
73 		return (LDBL_MAX * copysignl(LDBL_MAX, x));
74 	if (k <= -XTWOT_OFFSET - 1)
75 		return (LDBL_MIN * copysignl(LDBL_MIN, x));
76 	if (k > 0) {
77 		XSET_EXP(k, x);
78 		return (x);
79 	}
80 	k += XTWOT_OFFSET + 1;
81 	XSET_EXP(k, x);
82 	return (x * twomtm1);
83 }
84