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/* @(#)z_logarithmf.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.

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

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

 * Logarithm

 *

 * Input:

 *   x - floating point value

 *   ten - indicates base ten numbers

 *

 * Output:

 *   logarithm of x

 *

 * Description:

 *   This routine calculates logarithms.

 *

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

#include "fdlibm.h"

#include "zmath.h"

static const float a[] = { -0.5527074855 };

static const float b[] = { -0.6632718214e+1 };

static const float C1 = 0.693145752;

static const float C2 = 1.428606820e-06;

static const float C3 = 0.4342944819;

float

_DEFUN (logarithmf, (float, int),

        float x _AND

        int ten)

{

  int N;

  float f, w, z;

  /* Check for domain error here. */

  if (x <= 0.0)

    {

      errno = ERANGE;

      return (z_notanum_f.f);

    }

  /* Get the exponent and mantissa where x = f * 2^N. */

  f = frexpf (x, &N);

  z = f - 0.5;

  if (f > __SQRT_HALF)

    z = (z - 0.5) / (f * 0.5 + 0.5);

  else

    {

      N--;

      z /= (z * 0.5 + 0.5);

    }

  w = z * z;

  /* Use Newton's method with 4 terms. */

  z += z * w * (a[0]) / ((w + 1.0) * w + b[0]);

  if (N != 0)

    z = (N * C2 + z) + N * C1;

  if (ten)

    z *= C3;

  return (z);

}