log1pl.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.
*/
/*
* log1pl(x)
* Kahan's trick based on log(1+x)/x being a slow varying function.
*/
#include "libm.h"
#if defined(__x86)
#define __swapRD __swap87RD
#endif
long double
log1pl(long double x) {
long double y;
enum fp_direction_type rd;
if (x != x)
return (x + x);
if (x < -1.L)
return (logl(x));
y = 1.L + x;
if (y != 1.L) {
if (y == x)
x = logl(x);
else
x *= logl(y) / (y - 1.L);
}
if (rd != fp_nearest)
return (x);
}