1 /* Copyright (C) 2011-2017 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
22 1.Reduced x to positive by atanh(-x) = -atanh(x)
25 atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
29 atanh(x) = 0.5*log1p(2x+2x*x/(1-x))
32 atanh(x) is NaN if |x| > 1 with signal;
33 atanh(NaN) is that NaN with no signal;
34 atanh(+-1) is +-INF with signal.
41 #include <math_private.h>
43 static const float huge = 1e30;
46 __ieee754_atanhf (float x)
50 if (isless (xa, 0.5f))
52 if (__glibc_unlikely (xa < 0x1.0p-28f))
54 math_force_eval (huge + x);
55 math_check_force_underflow (x);
60 t = 0.5f * __log1pf (t + t * xa / (1.0f - xa));
62 else if (__glibc_likely (isless (xa, 1.0f)))
63 t = 0.5f * __log1pf ((xa + xa) / (1.0f - xa));
66 if (isgreater (xa, 1.0f))
67 return (x - x) / (x - x);
72 return __copysignf (t, x);
74 strong_alias (__ieee754_atanhf, __atanhf_finite)