| /* |
| * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code 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 General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* Tanh(x) |
| * Return the Hyperbolic Tangent of x |
| * |
| * Method : |
| * x -x |
| * e - e |
| * 0. tanh(x) is defined to be ----------- |
| * x -x |
| * e + e |
| * 1. reduce x to non-negative by tanh(-x) = -tanh(x). |
| * 2. 0 <= x <= 2**-55 : tanh(x) := x*(one+x) |
| * -t |
| * 2**-55 < x <= 1 : tanh(x) := -----; t = expm1(-2x) |
| * t + 2 |
| * 2 |
| * 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t=expm1(2x) |
| * t + 2 |
| * 22.0 < x <= INF : tanh(x) := 1. |
| * |
| * Special cases: |
| * tanh(NaN) is NaN; |
| * only tanh(0)=0 is exact for finite argument. |
| */ |
| |
| #include "fdlibm.h" |
| |
| #ifdef __STDC__ |
| static const double one=1.0, two=2.0, tiny = 1.0e-300; |
| #else |
| static double one=1.0, two=2.0, tiny = 1.0e-300; |
| #endif |
| |
| #ifdef __STDC__ |
| double tanh(double x) |
| #else |
| double tanh(x) |
| double x; |
| #endif |
| { |
| double t,z; |
| int jx,ix; |
| |
| /* High word of |x|. */ |
| jx = __HI(x); |
| ix = jx&0x7fffffff; |
| |
| /* x is INF or NaN */ |
| if(ix>=0x7ff00000) { |
| if (jx>=0) return one/x+one; /* tanh(+-inf)=+-1 */ |
| else return one/x-one; /* tanh(NaN) = NaN */ |
| } |
| |
| /* |x| < 22 */ |
| if (ix < 0x40360000) { /* |x|<22 */ |
| if (ix<0x3c800000) /* |x|<2**-55 */ |
| return x*(one+x); /* tanh(small) = small */ |
| if (ix>=0x3ff00000) { /* |x|>=1 */ |
| t = expm1(two*fabs(x)); |
| z = one - two/(t+two); |
| } else { |
| t = expm1(-two*fabs(x)); |
| z= -t/(t+two); |
| } |
| /* |x| > 22, return +-1 */ |
| } else { |
| z = one - tiny; /* raised inexact flag */ |
| } |
| return (jx>=0)? z: -z; |
| } |