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/* @(#)z_tanh.c 1.0 98/08/13 */
/*****************************************************************
* The following routines are coded directly from the algorithms
* and coefficients given in "Software Manual for the Elementary
* Functions" by William J. Cody, Jr. and William Waite, Prentice
* Hall, 1980.
*****************************************************************/
/*
FUNCTION
<<tanh>>, <<tanhf>>---hyperbolic tangent
INDEX
tanh
INDEX
tanhf
ANSI_SYNOPSIS
#include <math.h>
double tanh(double <[x]>);
float tanhf(float <[x]>);
TRAD_SYNOPSIS
#include <math.h>
double tanh(<[x]>)
double <[x]>;
float tanhf(<[x]>)
float <[x]>;
DESCRIPTION
<<tanh>> computes the hyperbolic tangent of
the argument <[x]>. Angles are specified in radians.
<<tanh(<[x]>)>> is defined as
. sinh(<[x]>)/cosh(<[x]>)
<<tanhf>> is identical, save that it takes and returns <<float>> values.
RETURNS
The hyperbolic tangent of <[x]> is returned.
PORTABILITY
<<tanh>> is ANSI C. <<tanhf>> is an extension.
*/
/******************************************************************
* Hyperbolic Tangent
*
* Input:
* x - floating point value
*
* Output:
* hyperbolic tangent of x
*
* Description:
* This routine calculates hyperbolic tangent.
*
*****************************************************************/
#include <float.h>
#include "fdlibm.h"
#include "zmath.h"
#ifndef _DOUBLE_IS_32BITS
static const double LN3_OVER2 = 0.54930614433405484570;
static const double p[] = { -0.16134119023996228053e+4,
-0.99225929672236083313e+2,
-0.96437492777225469787 };
static const double q[] = { 0.48402357071988688686e+4,
0.22337720718962312926e+4,
0.11274474380534949335e+3 };
double
_DEFUN (tanh, (double),
double x)
{
double f, res, g, P, Q, R;
f = fabs (x);
/* Check if the input is too big. */
if (f > BIGX)
res = 1.0;
else if (f > LN3_OVER2)
res = 1.0 - 2.0 / (exp (2 * f) + 1.0);
/* Check if the input is too small. */
else if (f < z_rooteps)
res = f;
/* Calculate the Taylor series. */
else
{
g = f * f;
P = (p[2] * g + p[1]) * g + p[0];
Q = ((g + q[2]) * g + q[1]) * g + q[0];
R = g * (P / Q);
res = f + f * R;
}
if (x < 0.0)
res = -res;
return (res);
}
#endif /* _DOUBLE_IS_32BITS */
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