log2l.c revision ddc0e0b53c661f6e439e3b7072b3ef353eadb4af
/*
* 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
* 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.
*/
/*
* log2l(x)
* RETURN THE BASE 2 LOGARITHM OF X
*
* Method:
* purge off 0,INF, and NaN.
* n = ilogb(x)
* if (n<0) n+=1
* z = scalbn(x,-n)
* LOG2(x) = n + (1/ln2)*log(x)
*/
#include "libm.h"
#include "longdouble.h"
static const long double
zero = 0.0L,
half = 0.5L,
one = 1.0L,
invln2 = 1.442695040888963407359924681001892137427e+0000L;
long double
log2l(long double x) {
int n;
return (logl(x));
n = ilogbl(x);
if (n < 0)
n += 1;
x = scalbnl(x, -n);
if (x == half)
return (n - one);
}