1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- 2 * 3 * ***** BEGIN LICENSE BLOCK ***** 4 * Version: MPL 1.1/GPL 2.0/LGPL 2.1 5 * 6 * The contents of this file are subject to the Mozilla Public License Version 7 * 1.1 (the "License"); you may not use this file except in compliance with 8 * the License. You may obtain a copy of the License at 9 * http://www.mozilla.org/MPL/ 10 * 11 * Software distributed under the License is distributed on an "AS IS" basis, 12 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License 13 * for the specific language governing rights and limitations under the 14 * License. 15 * 16 * The Original Code is Mozilla Communicator client code, released 17 * March 31, 1998. 18 * 19 * The Initial Developer of the Original Code is 20 * Sun Microsystems, Inc. 21 * Portions created by the Initial Developer are Copyright (C) 1998 22 * the Initial Developer. All Rights Reserved. 23 * 24 * Contributor(s): 25 * 26 * Alternatively, the contents of this file may be used under the terms of 27 * either of the GNU General Public License Version 2 or later (the "GPL"), 28 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"), 29 * in which case the provisions of the GPL or the LGPL are applicable instead 30 * of those above. If you wish to allow use of your version of this file only 31 * under the terms of either the GPL or the LGPL, and not to allow others to 32 * use your version of this file under the terms of the MPL, indicate your 33 * decision by deleting the provisions above and replace them with the notice 34 * and other provisions required by the GPL or the LGPL. If you do not delete 35 * the provisions above, a recipient may use your version of this file under 36 * the terms of any one of the MPL, the GPL or the LGPL. 37 * 38 * ***** END LICENSE BLOCK ***** */ 39 40 /* @(#)s_tanh.c 1.3 95/01/18 */ 41 /* 42 * ==================================================== 43 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 44 * 45 * Developed at SunSoft, a Sun Microsystems, Inc. business. 46 * Permission to use, copy, modify, and distribute this 47 * software is freely granted, provided that this notice 48 * is preserved. 49 * ==================================================== 50 */ 51 52 /* Tanh(x) 53 * Return the Hyperbolic Tangent of x 54 * 55 * Method : 56 * x -x 57 * e - e 58 * 0. tanh(x) is defined to be ----------- 59 * x -x 60 * e + e 61 * 1. reduce x to non-negative by tanh(-x) = -tanh(x). 62 * 2. 0 <= x <= 2**-55 : tanh(x) := x*(one+x) 63 * -t 64 * 2**-55 < x <= 1 : tanh(x) := -----; t = expm1(-2x) 65 * t + 2 66 * 2 67 * 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t=expm1(2x) 68 * t + 2 69 * 22.0 < x <= INF : tanh(x) := 1. 70 * 71 * Special cases: 72 * tanh(NaN) is NaN; 73 * only tanh(0)=0 is exact for finite argument. 74 */ 75 76 #include "fdlibm.h" 77 78 #ifdef __STDC__ 79 static const double one=1.0, two=2.0, tiny = 1.0e-300; 80 #else 81 static double one=1.0, two=2.0, tiny = 1.0e-300; 82 #endif 83 84 #ifdef __STDC__ fd_tanh(double x)85 double fd_tanh(double x) 86 #else 87 double fd_tanh(x) 88 double x; 89 #endif 90 { 91 double t,z; 92 int jx,ix; 93 fd_twoints u; 94 95 /* High word of |x|. */ 96 u.d = x; 97 jx = __HI(u); 98 ix = jx&0x7fffffff; 99 100 /* x is INF or NaN */ 101 if(ix>=0x7ff00000) { 102 if (jx>=0) return one/x+one; /* tanh(+-inf)=+-1 */ 103 else return one/x-one; /* tanh(NaN) = NaN */ 104 } 105 106 /* |x| < 22 */ 107 if (ix < 0x40360000) { /* |x|<22 */ 108 if (ix<0x3c800000) /* |x|<2**-55 */ 109 return x*(one+x); /* tanh(small) = small */ 110 if (ix>=0x3ff00000) { /* |x|>=1 */ 111 t = fd_expm1(two*fd_fabs(x)); 112 z = one - two/(t+two); 113 } else { 114 t = fd_expm1(-two*fd_fabs(x)); 115 z= -t/(t+two); 116 } 117 /* |x| > 22, return +-1 */ 118 } else { 119 z = one - tiny; /* raised inexact flag */ 120 } 121 return (jx>=0)? z: -z; 122 } 123