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jeremybenn |
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/* (C)Copyright 2001,2008, */
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/* International Business Machines Corporation, */
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/* Sony Computer Entertainment, Incorporated, */
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/* Toshiba Corporation, */
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/* */
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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 _EXP2F4_H_
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#define _EXP2F4_H_ 1
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#include <spu_intrinsics.h>
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#include "simdmath.h"
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/*
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* FUNCTION
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* vector float _exp2f4(vector float x)
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*
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* DESCRIPTION
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* The _exp2f4 function computes 2 raised to the input vector x.
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* Computation is performed by observing the 2^(a+b) = 2^a * 2^b.
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* We decompose x into a and b (above) by letting.
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* a = ceil(x), b = x - a;
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*
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* 2^a is easilty computed by placing a into the exponent
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* or a floating point number whose mantissa is all zeros.
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*
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* 2^b is computed using the following polynomial approximation.
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* (C. Hastings, Jr, 1955).
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*
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* __7__
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* \
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* \
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* 2^(-x) = / Ci*x^i
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* /____
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* i=1
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*
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* for x in the range 0.0 to 1.0
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*
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* C0 = 1.0
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* C1 = -0.9999999995
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* C2 = 0.4999999206
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* C3 = -0.1666653019
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* C4 = 0.0416573475
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* C5 = -0.0083013598
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* C6 = 0.0013298820
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* C7 = -0.0001413161
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*
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*/
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static __inline vector float _exp2f4(vector float x)
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{
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vector signed int ix;
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vector unsigned int overflow, underflow;
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vector float frac, frac2, frac4;
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vector float exp_int, exp_frac;
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vector float result;
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vector float hi, lo;
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vector float bias;
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/* Break in the input x into two parts ceil(x), x - ceil(x).
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*/
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bias = (vector float)(spu_rlmaska((vector signed int)(x), -31));
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bias = (vector float)(spu_andc(spu_splats((unsigned int)0x3F7FFFFF), (vector unsigned int)bias));
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ix = spu_convts(spu_add(x, bias), 0);
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frac = spu_sub(spu_convtf(ix, 0), x);
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frac = spu_mul(frac, spu_splats((float)SM_LN2));
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overflow = spu_rlmask(spu_cmpgt(ix, 128), -1);
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underflow = spu_cmpgt(ix, -128);
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exp_int = (vector float)spu_and((vector unsigned int)spu_sl(spu_add(ix, 127), 23), underflow);
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/* Instruction counts can be reduced if the polynomial was
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* computed entirely from nested (dependent) fma's. However,
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* to reduce the number of pipeline stalls, the polygon is evaluated
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* in two halves (hi amd lo).
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*/
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frac2 = spu_mul(frac, frac);
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frac4 = spu_mul(frac2, frac2);
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hi = spu_madd(frac, spu_splats(-0.0001413161f), spu_splats(0.0013298820f));
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hi = spu_madd(frac, hi, spu_splats(-0.0083013598f));
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hi = spu_madd(frac, hi, spu_splats(0.0416573475f));
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lo = spu_madd(frac, spu_splats(-0.1666653019f), spu_splats(0.4999999206f));
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lo = spu_madd(frac, lo, spu_splats(-0.9999999995f));
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lo = spu_madd(frac, lo, spu_splats(1.0f));
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exp_frac = spu_madd(frac4, hi, lo);
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ix = spu_add(ix, spu_rlmask((vector signed int)(exp_frac), -23));
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result = spu_mul(exp_frac, exp_int);
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/* Handle overflow */
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result = spu_or(result, (vector float)overflow);
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return (result);
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}
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#endif /* _EXP2F4_H_ */
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#endif /* __SPU__ */
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