1/* from: FreeBSD: head/lib/msun/src/e_atanh.c 176451 2008-02-22 02:30:36Z das */
2
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 *
13 */
14
15#include <sys/cdefs.h>
16
17#include "namespace.h"
18
19#include <float.h>
20#include <machine/ieee.h>
21
22#include "math.h"
23#include "math_private.h"
24
25__weak_alias(atanhl, _atanhl)
26
27#ifdef __HAVE_LONG_DOUBLE
28/*
29 * See e_atanh.c for complete comments.
30 *
31 * Converted to long double by David Schultz <das@FreeBSD.ORG> and
32 * Bruce D. Evans.
33 */
34
35/* EXP_TINY is the threshold below which we use atanh(x) ~= x. */
36#if LDBL_MANT_DIG == 64
37#define	EXP_TINY	-34
38#elif LDBL_MANT_DIG == 113
39#define	EXP_TINY	-58
40#else
41#error "Unsupported long double format"
42#endif
43
44#if LDBL_MAX_EXP != 0x4000
45/* We also require the usual expsign encoding. */
46#error "Unsupported long double format"
47#endif
48
49#define	BIAS	(LDBL_MAX_EXP - 1)
50
51static const double one = 1.0, huge = 1e300;
52static const double zero = 0.0;
53
54long double
55atanhl(long double x)
56{
57	long double t;
58	uint16_t hx, ix;
59
60	ENTERI();
61	GET_LDBL_EXPSIGN(hx, x);
62	ix = hx & 0x7fff;
63	if (ix >= 0x3fff)		/* |x| >= 1, or NaN or misnormal */
64	    RETURNI(fabsl(x) == 1 ? x / zero : (x - x) / (x - x));
65	if (ix < BIAS + EXP_TINY && (huge + x) > zero)
66	    RETURNI(x);			/* x is tiny */
67	SET_LDBL_EXPSIGN(x, ix);
68	if (ix < 0x3ffe) {		/* |x| < 0.5, or misnormal */
69	    t = x+x;
70	    t = 0.5*log1pl(t+t*x/(one-x));
71	} else
72	    t = 0.5*log1pl((x+x)/(one-x));
73	RETURNI((hx & 0x8000) == 0 ? t : -t);
74}
75#else
76long double
77atanhl(long double x)
78{
79	return atanh(x);
80}
81#endif
82