xref: /titanic_51/usr/src/lib/libm/common/m9x/scalblnf.c (revision b59c4a48daf5a1863ecac763711b497b2f8321e4)
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 scalblnf = __scalblnf
32 #endif
33 
34 #include "libm.h"
35 #include <float.h>		/* FLT_MAX, FLT_MIN */
36 
37 static const float twom25f = 2.98023223876953125e-8F;
38 #if defined(USE_FPSCALE) || defined(__x86)
39 static const float two23f = 8388608.0F;
40 #else
41 /*
42  * v: a non-zero subnormal |x|; returns [-22, 0]
43  */
44 static int
45 ilogbf_biased(unsigned v) {
46 	int r = -22;
47 
48 	if (v & 0xffff0000)
49 		r += 16, v >>= 16;
50 	if (v & 0xff00)
51 		r += 8, v >>= 8;
52 	if (v & 0xf0)
53 		r += 4, v >>= 4;
54 	v <<= 1;
55 	return (r + ((0xffffaa50 >> v) & 0x3));
56 }
57 #endif	/* defined(USE_FPSCALE) */
58 
59 float
60 scalblnf(float x, long n) {
61 	int *px = (int *) &x, ix, k;
62 
63 	ix = *px & ~0x80000000;
64 	k = ix >> 23;
65 	if (k == 0xff)
66 #if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
67 		return (ix > 0x7f800000 ? x * x : x);
68 #else
69 		return (x + x);
70 #endif
71 	if (ix == 0 || n == 0)
72 		return (x);
73 	if (k == 0) {
74 #if defined(USE_FPSCALE) || defined(__x86)
75 		x *= two23f;
76 		k = ((*px & ~0x80000000) >> 23) - 23;
77 #else
78 		k = ilogbf_biased(ix);
79 		*px = (*px & 0x80000000) | (ix << (-k + 1));
80 #endif
81 	}
82 	k += (int) n;
83 	if (n > 5000 || k > 0xfe)
84 		return (FLT_MAX * copysignf(FLT_MAX, x));
85 	if (n < -5000 || k <= -25)
86 		return (FLT_MIN * copysignf(FLT_MIN, x));
87 	if (k > 0) {
88 		*px = (*px & ~0x7f800000) | (k << 23);
89 		return (x);
90 	}
91 	k += 25;
92 	*px = (*px & ~0x7f800000) | (k << 23);
93 	return (x * twom25f);
94 }
95