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/* PROLOG END TAG zYx                                              */

#ifdef __SPU__

#ifndef _ATAND2_H_
#define _ATAND2_H_	1

#include <spu_intrinsics.h>

#include "simdmath.h"
#include "recipd2.h"
#include "logd2.h"
#include "acosd2.h"
#include "asind2.h"
#include "sqrtd2.h"

/*
 * FUNCTION
 *	vector double _atand2(vector double x)
 *
 * DESCRIPTION
 *	The _atand2 function computes the arc tangent of a vector of values x.
 *
 *	The arc tangent function is computed using the following relations:
 *	[0, 1]          :  arcsin(x1/sqrt(spu_add(x1squ + 1 )));
 *	(1, infinity]   :  PI/2 + atanf(-1/x)
 *	[-infinity, 0)  :  -arcsin(|x|)
 *
 */

static __inline vector double _atand2(vector double x)
{
    vector double signbit = spu_splats(-0.0);
    vector double oned    = spu_splats(1.0);
    vector double pi2     = spu_splats(SM_PI_2);
    vector double xabs, x1;
    vector double result;
    vector unsigned long long gt1;

    xabs = spu_andc(x, signbit);
    gt1  = spu_cmpgt(xabs, oned);

    /*
     * For x > 1, use the relation:
     * atan(x) = pi/2 - atan(1/x), x>1
     */
    x1 = spu_sel(xabs, _recipd2(xabs), gt1);

    vector double x1squ = spu_mul(x1, x1);

    result = _asind2(_divd2(x1, _sqrtd2(spu_add(x1squ, oned))));

    /*
     * For x > 1, use the relation: atan(x) = pi/2 - atan(1/x), x>1
     */
    result = spu_sel(result, spu_sub(pi2, result), gt1);

    /*
     * Antisymmetric function - preserve sign of x in result.
     */
    result = spu_sel(result, x, (vec_ullong2)signbit);

    return (result);
}

#endif /* _ATAND2_H_ */
#endif /* __SPU__ */