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  • Committer: Package Import Robot
  • Author(s): Dmitrijs Ledkovs
  • Date: 2013-07-05 10:12:24 UTC
  • Revision ID: package-import@ubuntu.com-20130705101224-6qo3e8jbz8p31aa1
Tags: upstream-0.20130705.1
Import upstream version 0.20130705.1

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android/bionic/libm/src/s_tanh.c
 
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/* @(#)s_tanh.c 5.1 93/09/24 */
 
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/*
 
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 * ====================================================
 
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 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 
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 *
 
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 * Developed at SunPro, a Sun Microsystems, Inc. business.
 
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 * Permission to use, copy, modify, and distribute this
 
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 * software is freely granted, provided that this notice
 
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 * is preserved.
 
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 * ====================================================
 
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 */
 
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#ifndef lint
 
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static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_tanh.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
 
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#endif
 
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/* Tanh(x)
 
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 * Return the Hyperbolic Tangent of x
 
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 *
 
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 * Method :
 
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 *                                     x    -x
 
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 *                                    e  - e
 
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 *      0. tanh(x) is defined to be -----------
 
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 *                                     x    -x
 
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 *                                    e  + e
 
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 *      1. reduce x to non-negative by tanh(-x) = -tanh(x).
 
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 *      2.  0      <= x <= 2**-55 : tanh(x) := x*(one+x)
 
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 *                                              -t
 
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 *          2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)
 
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 *                                             t + 2
 
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 *                                                   2
 
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 *          1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t=expm1(2x)
 
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 *                                                 t + 2
 
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 *          22.0   <  x <= INF    : tanh(x) := 1.
 
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 *
 
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 * Special cases:
 
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 *      tanh(NaN) is NaN;
 
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 *      only tanh(0)=0 is exact for finite argument.
 
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 */
 
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#include "math.h"
 
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#include "math_private.h"
 
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static const double one=1.0, two=2.0, tiny = 1.0e-300;
 
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double
 
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tanh(double x)
 
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{
 
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        double t,z;
 
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        int32_t jx,ix;
 
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    /* High word of |x|. */
 
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        GET_HIGH_WORD(jx,x);
 
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        ix = jx&0x7fffffff;
 
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    /* x is INF or NaN */
 
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        if(ix>=0x7ff00000) {
 
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            if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
 
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            else       return one/x-one;    /* tanh(NaN) = NaN */
 
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        }
 
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    /* |x| < 22 */
 
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        if (ix < 0x40360000) {          /* |x|<22 */
 
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            if (ix<0x3c800000)          /* |x|<2**-55 */
 
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                return x*(one+x);       /* tanh(small) = small */
 
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            if (ix>=0x3ff00000) {       /* |x|>=1  */
 
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                t = expm1(two*fabs(x));
 
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                z = one - two/(t+two);
 
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            } else {
 
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                t = expm1(-two*fabs(x));
 
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                z= -t/(t+two);
 
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            }
 
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    /* |x| > 22, return +-1 */
 
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        } else {
 
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            z = one - tiny;             /* raised inexact flag */
 
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        }
 
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        return (jx>=0)? z: -z;
 
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}