xref: /titanic_51/usr/src/lib/libm/common/R/scalbnf.c (revision 90b1de135fcfa7ce4adc9138a885aa94bbcef04f)
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 __scalbnf = scalbnf
31 
32 #include "libm.h"
33 #include <float.h>		/* FLT_MAX, FLT_MIN */
34 #include <stdlib.h>		/* abs */
35 
36 static const float twom25f = 2.98023223876953125e-8F;
37 #if defined(__x86)
38 static const float two23f = 8388608.0F;
39 #else
40 /*
41  * v: a non-zero subnormal |x|; returns [-22, 0]
42  */
43 static int
44 ilogbf_biased(unsigned v) {
45 	int r = -22;
46 
47 	if (v & 0xffff0000)
48 		r += 16, v >>= 16;
49 	if (v & 0xff00)
50 		r += 8, v >>= 8;
51 	if (v & 0xf0)
52 		r += 4, v >>= 4;
53 	v <<= 1;
54 	return (r + ((0xffffaa50 >> v) & 0x3));
55 }
56 #endif	/* defined(__x86) */
57 
58 float
59 scalbnf(float x, int n) {
60 	int *px = (int *) &x, ix, k;
61 
62 	ix = *px & ~0x80000000;
63 	k = ix >> 23;
64 	if (k == 0xff)
65 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
66 		return (ix > 0x7f800000 ? x * x : x);
67 #else
68 		return (x + x);
69 #endif
70 	if (ix == 0 || n == 0)
71 		return (x);
72 	if (k == 0) {
73 #if defined(__x86)
74 		x *= two23f;
75 		k = ((*px & ~0x80000000) >> 23) - 23;
76 #else
77 		k = ilogbf_biased(ix);
78 		*px = (*px & 0x80000000) | (ix << (-k + 1));
79 #endif
80 	}
81 	if ((unsigned) abs(n) >= 131072)	/* cast to unsigned for -2^31 */
82 		n >>= 1;		/* avoid subsequent integer overflow */
83 	k += n;
84 	if (k > 0xfe)
85 		return (FLT_MAX * copysignf(FLT_MAX, x));
86 	if (k <= -25)
87 		return (FLT_MIN * copysignf(FLT_MIN, x));
88 	if (k > 0) {
89 		*px = (*px & ~0x7f800000) | (k << 23);
90 		return (x);
91 	}
92 	k += 25;
93 	*px = (*px & ~0x7f800000) | (k << 23);
94 	return (x * twom25f);
95 }
96