summaryrefslogtreecommitdiff
path: root/libm/e_atanh.c
blob: fb36a1af1a2dc36695d4691742ece462cea930a9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/* __ieee754_atanh(x)
 * Method :
 *    1.Reduced x to positive by atanh(-x) = -atanh(x)
 *    2.For x>=0.5
 *                  1              2x                          x
 *	atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
 *                  2             1 - x                      1 - x
 *
 * 	For x<0.5
 *	atanh(x) = 0.5*log1p(2x+2x*x/(1-x))
 *
 * Special cases:
 *	atanh(x) is NaN if |x| > 1 with signal;
 *	atanh(NaN) is that NaN with no signal;
 *	atanh(+-1) is +-INF with signal.
 *
 */

#include "math.h"
#include "math_private.h"

static const double one = 1.0, huge = 1e300;

static const double zero = 0.0;

double __ieee754_atanh(double x)
{
	double t;
	int32_t hx,ix;
	u_int32_t lx;
	EXTRACT_WORDS(hx,lx,x);
	ix = hx&0x7fffffff;
	if ((ix|((lx|(-lx))>>31))>0x3ff00000) /* |x|>1 */
	    return (x-x)/(x-x);
	if(ix==0x3ff00000)
	    return x/zero;
	if(ix<0x3e300000&&(huge+x)>zero) return x;	/* x<2**-28 */
	SET_HIGH_WORD(x,ix);
	if(ix<0x3fe00000) {		/* x < 0.5 */
	    t = x+x;
	    t = 0.5*log1p(t+t*x/(one-x));
	} else
	    t = 0.5*log1p((x+x)/(one-x));
	if(hx>=0) return t; else return -t;
}

strong_alias(__ieee754_atanh, atanh)
libm_hidden_def(atanh)