136 lines
4.9 KiB
C
136 lines
4.9 KiB
C
/* -------------------------------------------------------------- */
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/* (C)Copyright 2007,2008, */
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/* International Business Machines Corporation */
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/* All Rights Reserved. */
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/* */
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/* Redistribution and use in source and binary forms, with or */
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/* without modification, are permitted provided that the */
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/* following conditions are met: */
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/* */
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/* - Redistributions of source code must retain the above copyright*/
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/* notice, this list of conditions and the following disclaimer. */
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/* */
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/* - Redistributions in binary form must reproduce the above */
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/* copyright notice, this list of conditions and the following */
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/* disclaimer in the documentation and/or other materials */
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/* provided with the distribution. */
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/* */
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/* - Neither the name of IBM Corporation nor the names of its */
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/* contributors may be used to endorse or promote products */
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/* derived from this software without specific prior written */
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/* permission. */
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/* */
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/* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND */
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/* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, */
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/* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF */
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/* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE */
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/* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR */
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/* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, */
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/* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT */
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/* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; */
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/* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) */
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/* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN */
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/* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR */
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/* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, */
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/* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
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/* -------------------------------------------------------------- */
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/* PROLOG END TAG zYx */
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#ifdef __SPU__
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#ifndef _TANHF4_H_
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#define _TANHF4_H_ 1
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#include <spu_intrinsics.h>
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#include "expf4.h"
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#include "divf4.h"
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#include "tanhd2.h"
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/*
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* FUNCTION
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* vector float _tanhf4(vector float x)
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*
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* DESCRIPTION
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* The _tanhf4 function computes the hyperbolic tangent for each
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* element of the input vector.
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*
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* We use the following to approximate tanh:
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*
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* |x| <= .25: Taylor Series
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* |x| > .25: tanh(x) = (exp(2x) - 1)/(exp(2x) + 1)
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*
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*
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* SPECIAL CASES:
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* - tanh(+/- 0) = +/-0
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* - tanh(+/- infinity) = +/- 1
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*
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*/
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static __inline vector float _tanhf4(vector float x)
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{
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vector float signbit = spu_splats(-0.0f);
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vector float onef = spu_splats(1.0f);
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vector float twof = spu_splats(2.0f);
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vector float xabs;
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vector float x2;
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vector unsigned int gttaylor;
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vector float e;
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vector float tresult;
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vector float eresult;
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vector float result;
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xabs = spu_andc(x, signbit);
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/*
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* This is where we switch from Taylor Series
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* to exponential formula.
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*/
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gttaylor = spu_cmpgt(xabs, spu_splats(0.25f));
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/*
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* Taylor Series Approximation
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*/
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x2 = spu_mul(x,x);
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tresult = spu_madd(x2, spu_splats((float)TANH_TAY06), spu_splats((float)TANH_TAY05));
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tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY04));
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tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY03));
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tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY02));
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tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY01));
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tresult = spu_mul(xabs, tresult);
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/*
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* Exponential Formula
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* Our expf4 function gives a more accurate result in general
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* with xabs instead of x for x<0. We correct for sign later.
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*/
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e = _expf4(spu_mul(xabs, twof));
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eresult = _divf4(spu_sub(e, onef), spu_add(e, onef));
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/*
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* Select Taylor or exp result.
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*/
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result = spu_sel(tresult, eresult, gttaylor);
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/*
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* Correct for accumulated truncation error when
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* tanh(x) should return 1.
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* Note that this also handles the special case of
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* x = +/- infinity.
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*/
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result = spu_sel(result, onef, spu_cmpgt(xabs, spu_splats(9.125f)));
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/*
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* Antisymmetric function - preserve sign bit of x
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* in the result.
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*/
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result = spu_sel(result, x, (vec_uint4)signbit);
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return result;
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}
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#endif /* _TANHF4_H_ */
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#endif /* __SPU__ */
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