1b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 2b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project/* @(#)s_tanh.c 1.3 95/01/18 */ 3b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project/* 4b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * ==================================================== 5b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 7b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * Developed at SunSoft, a Sun Microsystems, Inc. business. 8b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * Permission to use, copy, modify, and distribute this 9b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * software is freely granted, provided that this notice 10b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * is preserved. 11b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * ==================================================== 12b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project */ 13b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 14b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project/* Tanh(x) 15b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * Return the Hyperbolic Tangent of x 16b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 17b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * Method : 18b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * x -x 19b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * e - e 20b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 0. ieee_tanh(x) is defined to be ----------- 21b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * x -x 22b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * e + e 23b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 1. reduce x to non-negative by ieee_tanh(-x) = -ieee_tanh(x). 24b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 2. 0 <= x <= 2**-55 : ieee_tanh(x) := x*(one+x) 25b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * -t 26b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 2**-55 < x <= 1 : ieee_tanh(x) := -----; t = ieee_expm1(-2x) 27b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * t + 2 28b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 2 29b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 1 <= x <= 22.0 : ieee_tanh(x) := 1- ----- ; t=ieee_expm1(2x) 30b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * t + 2 31b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 22.0 < x <= INF : ieee_tanh(x) := 1. 32b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * 33b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * Special cases: 34b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * tanh(NaN) is NaN; 35b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project * only ieee_tanh(0)=0 is exact for finite argument. 36b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project */ 37b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 38b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#include "fdlibm.h" 39b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 40b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#ifdef __STDC__ 41b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Projectstatic const double one=1.0, two=2.0, tiny = 1.0e-300; 42b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#else 43b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Projectstatic double one=1.0, two=2.0, tiny = 1.0e-300; 44b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#endif 45b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 46b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#ifdef __STDC__ 47b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project double ieee_tanh(double x) 48b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#else 49b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project double ieee_tanh(x) 50b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project double x; 51b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project#endif 52b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project{ 53b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project double t,z; 54b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project int jx,ix; 55b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 56b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project /* High word of |x|. */ 57b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project jx = __HI(x); 58b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project ix = jx&0x7fffffff; 59b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 60b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project /* x is INF or NaN */ 61b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project if(ix>=0x7ff00000) { 62b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project if (jx>=0) return one/x+one; /* ieee_tanh(+-inf)=+-1 */ 63b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project else return one/x-one; /* ieee_tanh(NaN) = NaN */ 64b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project } 65b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project 66b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project /* |x| < 22 */ 67b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project if (ix < 0x40360000) { /* |x|<22 */ 68b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project if (ix<0x3c800000) /* |x|<2**-55 */ 69b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project return x*(one+x); /* ieee_tanh(small) = small */ 70b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project if (ix>=0x3ff00000) { /* |x|>=1 */ 71b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project t = ieee_expm1(two*ieee_fabs(x)); 72b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project z = one - two/(t+two); 73b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project } else { 74b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project t = ieee_expm1(-two*ieee_fabs(x)); 75b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project z= -t/(t+two); 76b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project } 77b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project /* |x| > 22, return +-1 */ 78b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project } else { 79b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project z = one - tiny; /* raised inexact flag */ 80b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project } 81b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project return (jx>=0)? z: -z; 82b07e1d9fd8d9e4e03698e0bd9bf77154c5390326The Android Open Source Project} 83