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#pragma weak __log1pl = log1pl
31
32/*
33 * log1pl(x)
34 * Kahan's trick based on log(1+x)/x being a slow varying function.
35 */
36
37#include "libm.h"
38
39#if defined(__x86)
40#define	__swapRD	__swap87RD
41#endif
42extern enum fp_direction_type __swapRD(enum fp_direction_type);
43
44long double
45log1pl(long double x) {
46	long double y;
47	enum fp_direction_type rd;
48
49	if (x != x)
50		return (x + x);
51	if (x < -1.L)
52		return (logl(x));
53	rd = __swapRD(fp_nearest);
54	y = 1.L + x;
55	if (y != 1.L) {
56		if (y == x)
57			x = logl(x);
58		else
59			x *= logl(y) / (y - 1.L);
60	}
61	if (rd != fp_nearest)
62		(void) __swapRD(rd);
63	return (x);
64}
65