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/* @(#)z_tanhf.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.
*****************************************************************/
/******************************************************************
* 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"
static const float LN3_OVER2 = 0.5493061443;
static const float p[] = { -0.2059432032,
-0.0009577527 };
static const float q[] = { 0.6178299136,
0.25 };
float
_DEFUN (tanhf, (float),
float x)
{
float f, res, g, P, Q, R;
f = fabsf (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_f)
res = f;
/* Calculate the Taylor series. */
else
{
g = f * f;
P = p[1] * g + p[0];
Q = (g + q[1]) * g + q[0];
R = g * (P / Q);
res = f + f * R;
}
if (x < 0.0)
res = -res;
return (res);
}
#ifdef _DOUBLE_IS_32BITS
double tanh (double x)
{
return (double) tanhf ((float) x);
}
#endif _DOUBLE_IS_32BITS
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