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/* @(#)z_expf.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.

 ******************************************************************/

/******************************************************************

 * Exponential Function

 *

 * Input:

 *   x - floating point value

 *

 * Output:

 *   e raised to x.

 *

 * Description:

 *   This routine returns e raised to the xth power.

 *

 *****************************************************************/

#include <float.h>

#include "fdlibm.h"

#include "zmath.h"

static const float INV_LN2 = 1.442695040;

static const float LN2 = 0.693147180;

static const float p[] = { 0.249999999950, 0.00416028863 };

static const float q[] = { 0.5, 0.04998717878 };

float

_DEFUN (expf, (float),

        float x)

{

  int N;

  float g, z, R, P, Q;

  switch (numtestf (x))

    {

      case NAN:

        errno = EDOM;

        return (x);

      case INF:

        errno = ERANGE;

        if (isposf (x))

          return (z_infinity_f.f);

        else

          return (0.0);

      case 0:

        return (1.0);

    }

  /* Check for out of bounds. */

  if (x > BIGX || x < SMALLX)

    {

      errno = ERANGE;

      return (x);

    }

  /* Check for a value too small to calculate. */

  if (-z_rooteps_f < x && x < z_rooteps_f)

    {

      return (1.0);

    }

  /* Calculate the exponent. */

  if (x < 0.0)

    N = (int) (x * INV_LN2 - 0.5);

  else

    N = (int) (x * INV_LN2 + 0.5);

  /* Construct the mantissa. */

  g = x - N * LN2;

  z = g * g;

  P = g * (p[1] * z + p[0]);

  Q = q[1] * z + q[0];

  R = 0.5 + P / (Q - P);

  /* Return the floating point value. */

  N++;

  return (ldexpf (R, N));

}

#ifdef _DOUBLE_IS_32BITS

double exp (double x)

{

  return (double) expf ((float) x);

}

#endif /* _DOUBLE_IS_32BITS */