Subversion Repositories or1k

/* @(#)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