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/* @(#)z_asinef.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.

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

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

 * Arcsine

 *

 * Input:

 *   x - floating point value

 *   acosine - indicates acos calculation

 *

 * Output:

 *   Arcsine of x.

 *

 * Description:

 *   This routine calculates arcsine / arccosine.

 *

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

#include "fdlibm.h"

#include "zmath.h"

static const float p[] = { 0.933935835, -0.504400557 };

static const float q[] = { 0.560363004e+1, -0.554846723e+1 };

static const float a[] = { 0.0, 0.785398163 };

static const float b[] = { 1.570796326, 0.785398163 };

float

_DEFUN (asinef, (float, int),

        float x _AND

        int acosine)

{

  int flag, i;

  int branch = 0;

  float g, res, R, P, Q, y;

  /* Check for special values. */

  i = numtestf (x);

  if (i == NAN || i == INF)

    {

      errno = EDOM;

      if (i == NAN)

        return (x);

      else

        return (z_infinity_f.f);

    }

  y = fabsf (x);

  flag = acosine;

  if (y > 0.5)

    {

      i = 1 - flag;

      /* Check for range error. */

      if (y > 1.0)

        {

          errno = ERANGE;

          return (z_notanum_f.f);

        }

      g = (1 - y) / 2.0;

      y = -2 * sqrt (g);

      branch = 1;

    }

  else

    {

      i = flag;

      if (y < z_rooteps_f)

        res = y;

      else

        g = y * y;

    }

  if (y >= z_rooteps_f || branch == 1)

    {

      /* Calculate the Taylor series. */

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

      Q = (g + q[1]) * g + q[0];

      R = P / Q;

      res = y + y * R;

    }

  /* Calculate asine or acose. */

  if (flag == 0)

    {

      res = (a[i] + res) + a[i];

      if (x < 0.0)

        res = -res;

    }

  else

    {

      if (x < 0.0)

        res = (b[i] + res) + b[i];

      else

        res = (a[i] - res) + a[i];

    }

  return (res);

}