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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.17.0/] [newlib/] [libm/] [machine/] [spu/] [headers/] [log2f4.h] - Rev 310
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/* -------------------------------------------------------------- */ /* (C)Copyright 2001,2008, */ /* 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. */ /* */ /* 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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