xref: /titanic_44/usr/src/lib/libm/common/R/logbf.c (revision ddc0e0b53c661f6e439e3b7072b3ef353eadb4af)
125c28e83SPiotr Jasiukajtis /*
225c28e83SPiotr Jasiukajtis  * CDDL HEADER START
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725c28e83SPiotr Jasiukajtis  *
825c28e83SPiotr Jasiukajtis  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
925c28e83SPiotr Jasiukajtis  * or http://www.opensolaris.org/os/licensing.
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1525c28e83SPiotr Jasiukajtis  * If applicable, add the following below this CDDL HEADER, with the
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2125c28e83SPiotr Jasiukajtis 
2225c28e83SPiotr Jasiukajtis /*
2325c28e83SPiotr Jasiukajtis  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
2425c28e83SPiotr Jasiukajtis  */
2525c28e83SPiotr Jasiukajtis /*
2625c28e83SPiotr Jasiukajtis  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
2725c28e83SPiotr Jasiukajtis  * Use is subject to license terms.
2825c28e83SPiotr Jasiukajtis  */
2925c28e83SPiotr Jasiukajtis 
30*ddc0e0b5SRichard Lowe #pragma weak __logbf = logbf
3125c28e83SPiotr Jasiukajtis 
3225c28e83SPiotr Jasiukajtis #include "libm.h"
3325c28e83SPiotr Jasiukajtis #include "xpg6.h"	/* __xpg6 */
3425c28e83SPiotr Jasiukajtis #define	_C99SUSv3_logb	_C99SUSv3_logb_subnormal_is_like_ilogb
3525c28e83SPiotr Jasiukajtis 
361ec68d33SRichard Lowe #if defined(__x86)
3725c28e83SPiotr Jasiukajtis static const float two25 = 33554432.0F;
3825c28e83SPiotr Jasiukajtis #else
3925c28e83SPiotr Jasiukajtis /*
4025c28e83SPiotr Jasiukajtis  * v: a non-zero subnormal |x|
4125c28e83SPiotr Jasiukajtis  */
4225c28e83SPiotr Jasiukajtis static int
ilogbf_subnormal(unsigned v)4325c28e83SPiotr Jasiukajtis ilogbf_subnormal(unsigned v) {
4425c28e83SPiotr Jasiukajtis 	int r = -126 - 23;
4525c28e83SPiotr Jasiukajtis 
4625c28e83SPiotr Jasiukajtis 	if (v & 0xffff0000)
4725c28e83SPiotr Jasiukajtis 		r += 16, v >>= 16;
4825c28e83SPiotr Jasiukajtis 	if (v & 0xff00)
4925c28e83SPiotr Jasiukajtis 		r += 8, v >>= 8;
5025c28e83SPiotr Jasiukajtis 	if (v & 0xf0)
5125c28e83SPiotr Jasiukajtis 		r += 4, v >>= 4;
5225c28e83SPiotr Jasiukajtis 	v <<= 1;
5325c28e83SPiotr Jasiukajtis 	return (r + ((0xffffaa50 >> v) & 0x3));
5425c28e83SPiotr Jasiukajtis }
551ec68d33SRichard Lowe #endif	/* defined(__x86) */
5625c28e83SPiotr Jasiukajtis 
5725c28e83SPiotr Jasiukajtis static float
raise_division(float t)5825c28e83SPiotr Jasiukajtis raise_division(float t) {
5925c28e83SPiotr Jasiukajtis #pragma STDC FENV_ACCESS ON
6025c28e83SPiotr Jasiukajtis 	static const float zero = 0.0F;
6125c28e83SPiotr Jasiukajtis 	return (t / zero);
6225c28e83SPiotr Jasiukajtis }
6325c28e83SPiotr Jasiukajtis 
6425c28e83SPiotr Jasiukajtis float
logbf(float x)6525c28e83SPiotr Jasiukajtis logbf(float x) {
6625c28e83SPiotr Jasiukajtis 	int k = *((int *) &x) & ~0x80000000;
6725c28e83SPiotr Jasiukajtis 
6825c28e83SPiotr Jasiukajtis 	if (k < 0x00800000) {
6925c28e83SPiotr Jasiukajtis 		if (k == 0)
7025c28e83SPiotr Jasiukajtis 			return (raise_division(-1.0F));
7125c28e83SPiotr Jasiukajtis 		else if ((__xpg6 & _C99SUSv3_logb) != 0) {
721ec68d33SRichard Lowe #if defined(__x86)
7325c28e83SPiotr Jasiukajtis 			x *= two25;
7425c28e83SPiotr Jasiukajtis 			return ((float) (((*((int *) &x) & 0x7f800000) >> 23) -
7525c28e83SPiotr Jasiukajtis 				152));
7625c28e83SPiotr Jasiukajtis #else
7725c28e83SPiotr Jasiukajtis 			return ((float) ilogbf_subnormal(k));
7825c28e83SPiotr Jasiukajtis #endif
7925c28e83SPiotr Jasiukajtis 		} else
8025c28e83SPiotr Jasiukajtis 			return (-126.F);
8125c28e83SPiotr Jasiukajtis 	} else if (k < 0x7f800000)
8225c28e83SPiotr Jasiukajtis 		return ((float) ((k >> 23) - 127));
8325c28e83SPiotr Jasiukajtis 	else
8425c28e83SPiotr Jasiukajtis 		return (x * x);
8525c28e83SPiotr Jasiukajtis }
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