| /* Copyright (C) 2011-2014 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Ulrich Drepper <drepper@gmail.com>, 2011. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| |
| /* __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 <inttypes.h> |
| #include <math.h> |
| #include <math_private.h> |
| |
| static const double huge = 1e300; |
| |
| double |
| __ieee754_atanh (double x) |
| { |
| double xa = fabs (x); |
| double t; |
| if (isless (xa, 0.5)) |
| { |
| if (__builtin_expect (xa < 0x1.0p-28, 0)) |
| { |
| math_force_eval (huge + x); |
| return x; |
| } |
| |
| t = xa + xa; |
| t = 0.5 * __log1p (t + t * xa / (1.0 - xa)); |
| } |
| else if (__builtin_expect (isless (xa, 1.0), 1)) |
| t = 0.5 * __log1p ((xa + xa) / (1.0 - xa)); |
| else |
| { |
| if (isgreater (xa, 1.0)) |
| return (x - x) / (x - x); |
| |
| return x / 0.0; |
| } |
| |
| return __copysign (t, x); |
| } |
| strong_alias (__ieee754_atanh, __atanh_finite) |
