1/* s_atanhl.c -- long double version of s_atan.c.
2 * Conversion to long double by Ulrich Drepper,
3 * Cygnus Support, drepper@cygnus.com.
4 */
5
6/*
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 *
10 * Developed at SunPro, a Sun Microsystems, Inc. business.
11 * Permission to use, copy, modify, and distribute this
12 * software is freely granted, provided that this notice
13 * is preserved.
14 * ====================================================
15 */
16
17/* atanhq(x)
18 * Method :
19 *    1.Reduced x to positive by atanh(-x) = -atanh(x)
20 *    2.For x>=0.5
21 *                   1              2x                          x
22 *	atanhl(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
23 *                   2             1 - x                      1 - x
24 *
25 *	For x<0.5
26 *	atanhl(x) = 0.5*log1pq(2x+2x*x/(1-x))
27 *
28 * Special cases:
29 *	atanhl(x) is NaN if |x| > 1 with signal;
30 *	atanhl(NaN) is that NaN with no signal;
31 *	atanhl(+-1) is +-INF with signal.
32 *
33 */
34
35#include "quadmath-imp.h"
36
37static const __float128 one = 1, huge = 1e4900Q;
38
39static const __float128 zero = 0;
40
41__float128
42atanhq(__float128 x)
43{
44	__float128 t;
45	uint32_t jx, ix;
46	ieee854_float128 u;
47
48	u.value = x;
49	jx = u.words32.w0;
50	ix = jx & 0x7fffffff;
51	u.words32.w0 = ix;
52	if (ix >= 0x3fff0000) /* |x| >= 1.0 or infinity or NaN */
53	  {
54	    if (u.value == one)
55	      return x/zero;
56	    else
57	      return (x-x)/(x-x);
58	  }
59	if(ix<0x3fc60000 && (huge+x)>zero)	/* x < 2^-57 */
60	  {
61	    math_check_force_underflow (x);
62	    return x;
63	  }
64
65	if(ix<0x3ffe0000) {		/* x < 0.5 */
66	    t = u.value+u.value;
67	    t = 0.5*log1pq(t+t*u.value/(one-u.value));
68	} else
69	    t = 0.5*log1pq((u.value+u.value)/(one-u.value));
70	if(jx & 0x80000000) return -t; else return t;
71}
72