<iso646.h>: Avoid conflicts w/ C++ keywords.
[dragonfly.git] / lib / libm / src / e_atanh.c
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1/* @(#)e_atanh.c 5.1 93/09/24 */
2/*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 *
12 * $NetBSD: e_atanh.c,v 1.11 2002/05/26 22:01:49 wiz Exp $
13 * $DragonFly: src/lib/libm/src/e_atanh.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
14 */
15
16/* atanh(x)
17 * Method :
18 * 1.Reduced x to positive by atanh(-x) = -atanh(x)
19 * 2.For x>=0.5
20 * 1 2x x
21 * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
22 * 2 1 - x 1 - x
23 *
24 * For x<0.5
25 * atanh(x) = 0.5*log1p(2x+2x*x/(1-x))
26 *
27 * Special cases:
28 * atanh(x) is NaN if |x| > 1 with signal;
29 * atanh(NaN) is that NaN with no signal;
30 * atanh(+-1) is +-INF with signal.
31 *
32 */
33
34#include <math.h>
35#include "math_private.h"
36
37static const double one = 1.0, huge = 1e300;
38
39static const double zero = 0.0;
40
41double
42atanh(double x)
43{
44 double t;
45 int32_t hx,ix;
46 u_int32_t lx;
47 EXTRACT_WORDS(hx,lx,x);
48 ix = hx&0x7fffffff;
49 if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */
50 return (x-x)/(x-x);
51 if(ix==0x3ff00000)
52 return x/zero;
53 if(ix<0x3e300000&&(huge+x)>zero) return x; /* x<2**-28 */
54 SET_HIGH_WORD(x,ix);
55 if(ix<0x3fe00000) { /* x < 0.5 */
56 t = x+x;
57 t = 0.5*log1p(t+t*x/(one-x));
58 } else
59 t = 0.5*log1p((x+x)/(one-x));
60 if(hx>=0) return t; else return -t;
61}