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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.17.0/] [newlib/] [libm/] [machine/] [spu/] [headers/] [exp2f4.h] - Blame information for rev 158

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1 148 jeremybenn
/* --------------------------------------------------------------  */
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/* (C)Copyright 2001,2008,                                         */
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/* International Business Machines Corporation,                    */
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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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