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125 lines
3.7 KiB
C
125 lines
3.7 KiB
C
/*
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(C) Copyright 2001,2006,
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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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All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright notice,
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this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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* Neither the names of the copyright holders nor the names of their
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contributors may be used to endorse or promote products derived from this
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software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
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OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef _LOG2F_H_
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#define _LOG2F_H_ 1
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#include <spu_intrinsics.h>
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#include "headers/dom_chkf_less_than.h"
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/*
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* FUNCTION
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* float _log2f(float x)
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*
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* DESCRIPTION
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* _log2f computes log (base 2) of the input value x. The log2f
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* function is approximated as a polynomial of order 8
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* (C. Hastings, Jr, 1955).
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*
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* __8__
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* \
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* \
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* log2f(1+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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* C1 = 1.4426898816672
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* C2 = -0.72116591947498
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* C3 = 0.47868480909345
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* C4 = -0.34730547155299
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* C5 = 0.24187369696082
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* C6 = -0.13753123777116
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* C7 = 0.052064690894143
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* C8 = -0.0093104962134977
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*
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* This function assumes that x is a non-zero positive value.
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*/
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static __inline float _log2f(float x)
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{
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union {
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unsigned int ui;
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float f;
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} in;
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int exponent;
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float result;
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float x2, x4;
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float hi, lo;
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vector float vx;
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vector float vc = { 0.0, 0.0, 0.0, 0.0 };
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in.f = x;
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/* Extract the exponent from the input X.
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*/
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exponent = (signed)((in.ui >> 23) & 0xFF) - 127;
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/* Compute the remainder after removing the exponent.
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*/
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in.ui -= exponent << 23;
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/* Calculate the log2 of the remainder using the polynomial
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* approximation.
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*/
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x = in.f - 1.0f;
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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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x2 = x * x;
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x4 = x2 * x2;
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hi = -0.0093104962134977f*x + 0.052064690894143f;
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hi = hi*x - 0.13753123777116f;
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hi = hi*x + 0.24187369696082f;
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hi = hi*x - 0.34730547155299f;
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lo = 0.47868480909345f *x - 0.72116591947498f;
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lo = lo*x + 1.4426898816672f;
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lo = lo*x;
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result = hi*x4 + lo;
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/* Add the exponent back into the result.
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*/
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result += (float)(exponent);
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#ifndef _IEEE_LIBM
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vx = spu_promote(x, 0);
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dom_chkf_less_than(vx, vc);
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#endif
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return (result);
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}
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#endif /* _LOG2F_H_ */
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