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/* PROLOG END TAG zYx                                              */

#ifdef __SPU__

#ifndef _ATANF4_H_

#define _ATANF4_H_      1

#include <spu_intrinsics.h>

#include "simdmath.h"

#include "recipf4.h"

/*

 * FUNCTION

 *      vector float _atanf4(vector float x)

 *

 * DESCRIPTION

 *      The _atanf4 function computes the arc tangent of a vector of values x;

 *      that is the values whose tangent is x.

 *

 *      The _atanf4 function returns the arc tangents in radians and the value

 *      is mathematically defined to be in the range -PI/2 to PI/2.

 *

 *      The arc tangent function is computed using a polynomial approximation

 *      (B. Carlson, M. Goldstein, Los Alamos Scientific Laboratory, 1955).

 *                __8__

 *                \

 *                 \

 *      atan(x) =  /    Ci*x^(2*i+1)

 *                /____

 *                 i=0

 *

 *      for x in the range -1 to 1. The remaining regions are defined to be:

 *

 *      [1, infinity]   :  PI/2 + atanf(-1/x)

 *      [-infinity, -1] : -PI/2 + atanf(-1/x)

 *

 */

static __inline vector float _atanf4(vector float x)

{

  vector float bias;

  vector float x2, x3, x4, x8, x9;

  vector float hi, lo;

  vector float result;

  vector float inv_x;

  vector unsigned int sign;

  vector unsigned int select;

  sign = spu_sl(spu_rlmask((vector unsigned int)x, -31), 31);

  inv_x = _recipf4(x);

  inv_x = (vector float)spu_xor((vector unsigned int)inv_x, spu_splats(0x80000000));

  select = (vector unsigned int)spu_cmpabsgt(x, spu_splats(1.0f));

  bias = (vector float)spu_or(sign, (vector unsigned int)(spu_splats((float)SM_PI_2)));

  bias = (vector float)spu_and((vector unsigned int)bias, select);

  x = spu_sel(x, inv_x, select);

  /* Instruction counts can be reduced if the polynomial was

   * computed entirely from nested (dependent) fma's. However,

   * to reduce the number of pipeline stalls, the polygon is evaluated

   * in two halves(hi and lo).

   */

  bias = spu_add(bias, x);

  x2 = spu_mul(x, x);

  x3 = spu_mul(x2, x);

  x4 = spu_mul(x2, x2);

  x8 = spu_mul(x4, x4);

  x9 = spu_mul(x8, x);

  hi = spu_madd(spu_splats(0.0028662257f), x2, spu_splats(-0.0161657367f));

  hi = spu_madd(hi, x2, spu_splats(0.0429096138f));

  hi = spu_madd(hi, x2, spu_splats(-0.0752896400f));

  hi = spu_madd(hi, x2, spu_splats(0.1065626393f));

  lo = spu_madd(spu_splats(-0.1420889944f), x2, spu_splats(0.1999355085f));

  lo = spu_madd(lo, x2, spu_splats(-0.3333314528f));

  lo = spu_madd(lo, x3, bias);

  result = spu_madd(hi, x9, lo);

  return (result);

}

#endif /* _ATANF4_H_ */

#endif /* __SPU__ */