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/* -------------------------------------------------------------- */
/* (C)Copyright 2006,2007, */
/* International Business Machines Corporation, */
/* Sony Computer Entertainment, Incorporated, */
/* Toshiba Corporation, */
/* */
/* All Rights Reserved. */
/* */
/* Redistribution and use in source and binary forms, with or */
/* without modification, are permitted provided that the */
/* following conditions are met: */
/* */
/* - Redistributions of source code must retain the above copyright*/
/* notice, this list of conditions and the following disclaimer. */
/* */
/* - Redistributions in binary form must reproduce the above */
/* copyright notice, this list of conditions and the following */
/* disclaimer in the documentation and/or other materials */
/* provided with the distribution. */
/* */
/* - Neither the name of IBM Corporation nor the names of its */
/* contributors may be used to endorse or promote products */
/* derived from this software without specific prior written */
/* permission. */
/* Redistributions of source code must retain the above copyright */
/* notice, this list of conditions and the following disclaimer. */
/* */
/* Redistributions in binary form must reproduce the above */
/* copyright notice, this list of conditions and the following */
/* disclaimer in the documentation and/or other materials */
/* provided with the distribution. */
/* */
/* Neither the name of IBM Corporation nor the names of its */
/* contributors may be used to endorse or promote products */
/* derived from this software without specific prior written */
/* permission. */
/* */
/* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND */
/* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, */
/* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF */
/* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE */
/* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR */
/* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, */
/* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT */
/* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; */
/* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) */
/* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN */
/* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR */
/* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, */
/* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
/* -------------------------------------------------------------- */
/* PROLOG END TAG zYx */
#ifdef __SPU__
#ifndef _LOG2F4_H_
#define _LOG2F4_H_ 1
#include <spu_intrinsics.h>
/*
* FUNCTION
* vector float _log2f4(vector float x)
*
* DESCRIPTION
* The _log2f4 function computes log (base 2) on a vector if inputs
* values x. The _log2f4 function is approximated as a polynomial of
* order 8 (C. Hastings, Jr, 1955).
*
* __8__
* \
* \
* log2f(1+x) = / Ci*x^i
* /____
* i=1
*
* for x in the range 0.0 to 1.0
*
* C1 = 1.4426898816672
* C2 = -0.72116591947498
* C3 = 0.47868480909345
* C4 = -0.34730547155299
* C5 = 0.24187369696082
* C6 = -0.13753123777116
* C7 = 0.052064690894143
* C8 = -0.0093104962134977
*
* This function assumes that x is a non-zero positive value.
*
*/
static __inline vector float _log2f4(vector float x)
{
vector signed int exponent;
vector float result;
vector float x2, x4;
vector float hi, lo;
/* Extract the exponent from the input X.
*/
exponent = (vector signed int)spu_and(spu_rlmask((vector unsigned int)(x), -23), 0xFF);
exponent = spu_add(exponent, -127);
/* Compute the remainder after removing the exponent.
*/
x = (vector float)spu_sub((vector signed int)(x), spu_sl(exponent, 23));
/* Calculate the log2 of the remainder using the polynomial
* approximation.
*/
x = spu_sub(x, spu_splats(1.0f));
/* 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 amd lo).
*/
x2 = spu_mul(x, x);
x4 = spu_mul(x2, x2);
hi = spu_madd(x, spu_splats(-0.0093104962134977f), spu_splats(0.052064690894143f));
hi = spu_madd(x, hi, spu_splats(-0.13753123777116f));
hi = spu_madd(x, hi, spu_splats( 0.24187369696082f));
hi = spu_madd(x, hi, spu_splats(-0.34730547155299f));
lo = spu_madd(x, spu_splats(0.47868480909345f), spu_splats(-0.72116591947498f));
lo = spu_madd(x, lo, spu_splats(1.4426898816672f));
lo = spu_mul(x, lo);
result = spu_madd(x4, hi, lo);
/* Add the exponent back into the result.
*/
result = spu_add(result, spu_convtf(exponent, 0));
return (result);
}
#endif /* _LOG2F4_H_ */
#endif /* __SPU__ */
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