xref: /illumos-gate/usr/src/lib/libm/common/R/ilogbf.c (revision 862246c1516ca78c11bef09650987f3d7171b2c9)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
 */
/*
 * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma weak __ilogbf = ilogbf

#include "libm.h"
#include "xpg6.h"	/* __xpg6 */

#if defined(__x86)
static const float two25 = 33554432.0F;
#else
/*
 * v: a non-zero subnormal |x|
 */
static int
ilogbf_subnormal(unsigned v) {
	int r = -126 - 23;

	if (v & 0xffff0000)
		r += 16, v >>= 16;
	if (v & 0xff00)
		r += 8, v >>= 8;
	if (v & 0xf0)
		r += 4, v >>= 4;
	v <<= 1;
	return (r + ((0xffffaa50 >> v) & 0x3));
}
#endif	/* defined(__x86) */

static int
raise_invalid(int v) {	/* SUSv3 requires ilogbf(0,+/-Inf,NaN) raise invalid */
#ifndef lint
	if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
		static const double zero = 0.0;
		volatile double dummy __unused;

		dummy = zero / zero;
	}
#endif
	return (v);
}

int
ilogbf(float x) {
	int k = *((int *) &x) & ~0x80000000;

	if (k < 0x00800000) {
		if (k == 0)
			return (raise_invalid(0x80000001));
		else {
#if defined(__x86)
			x *= two25;
			return (((*((int *) &x) & 0x7f800000) >> 23) - 152);
#else
			return (ilogbf_subnormal(k));
#endif
		}
	} else if (k < 0x7f800000)
		return ((k >> 23) - 127);
	else
		return (raise_invalid(0x7fffffff));
}