Subversion Repositories openrisc_2011-10-31

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/* PROLOG END TAG zYx                                              */

#ifdef __SPU__

#ifndef _TANHF4_H_

#define _TANHF4_H_      1

#include <spu_intrinsics.h>

#include "expf4.h"

#include "divf4.h"

#include "tanhd2.h"

/*

 * FUNCTION

 *  vector float _tanhf4(vector float x)

 *

 * DESCRIPTION

 *      The _tanhf4 function computes the hyperbolic tangent for each

 *      element of the input vector.

 *

 *      We use the following to approximate tanh:

 *

 *      |x| <= .25:   Taylor Series

 *      |x| >  .25:   tanh(x) = (exp(2x) - 1)/(exp(2x) + 1)

 *

 *

 * SPECIAL CASES:

 *  - tanh(+/- 0) = +/-0

 *  - tanh(+/- infinity) = +/- 1

 *

 */

static __inline vector float _tanhf4(vector float x)

{

    vector float signbit = spu_splats(-0.0f);

    vector float onef    = spu_splats(1.0f);

    vector float twof    = spu_splats(2.0f);

    vector float xabs;

    vector float x2;

    vector unsigned int gttaylor;

    vector float e;

    vector float tresult;

    vector float eresult;

    vector float result;

    xabs = spu_andc(x, signbit);

    /*

     * This is where we switch from Taylor Series

     * to exponential formula.

     */

    gttaylor = spu_cmpgt(xabs, spu_splats(0.25f));

    /*

     * Taylor Series Approximation

     */

    x2 = spu_mul(x,x);

    tresult = spu_madd(x2, spu_splats((float)TANH_TAY06), spu_splats((float)TANH_TAY05));

    tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY04));

    tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY03));

    tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY02));

    tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY01));

    tresult = spu_mul(xabs, tresult);

    /*

     * Exponential Formula

     * Our expf4 function gives a more accurate result in general

     * with xabs instead of x for x<0. We correct for sign later.

     */

    e = _expf4(spu_mul(xabs, twof));

    eresult = _divf4(spu_sub(e, onef), spu_add(e, onef));

    /*

     * Select Taylor or exp result.

     */

    result = spu_sel(tresult, eresult, gttaylor);

    /*

     * Correct for accumulated truncation error when

     * tanh(x) should return 1.

     * Note that this also handles the special case of

     * x = +/- infinity.

     */

    result = spu_sel(result, onef, spu_cmpgt(xabs, spu_splats(9.125f)));

    /*

     * Antisymmetric function - preserve sign bit of x

     * in the result.

     */

    result = spu_sel(result, x, (vec_uint4)signbit);

    return result;

}

#endif /* _TANHF4_H_ */

#endif /* __SPU__ */