Retro68/gcc/newlib/libm/machine/spu/headers/exp2f4.h
2012-03-27 01:51:53 +02:00

135 lines
5.4 KiB
C

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/* PROLOG END TAG zYx */
#ifdef __SPU__
#ifndef _EXP2F4_H_
#define _EXP2F4_H_ 1
#include <spu_intrinsics.h>
#include "simdmath.h"
/*
* FUNCTION
* vector float _exp2f4(vector float x)
*
* DESCRIPTION
* The _exp2f4 function computes 2 raised to the input vector x.
* Computation is performed by observing the 2^(a+b) = 2^a * 2^b.
* We decompose x into a and b (above) by letting.
* a = ceil(x), b = x - a;
*
* 2^a is easilty computed by placing a into the exponent
* or a floating point number whose mantissa is all zeros.
*
* 2^b is computed using the following polynomial approximation.
* (C. Hastings, Jr, 1955).
*
* __7__
* \
* \
* 2^(-x) = / Ci*x^i
* /____
* i=1
*
* for x in the range 0.0 to 1.0
*
* C0 = 1.0
* C1 = -0.9999999995
* C2 = 0.4999999206
* C3 = -0.1666653019
* C4 = 0.0416573475
* C5 = -0.0083013598
* C6 = 0.0013298820
* C7 = -0.0001413161
*
*/
static __inline vector float _exp2f4(vector float x)
{
vector signed int ix;
vector unsigned int overflow, underflow;
vector float frac, frac2, frac4;
vector float exp_int, exp_frac;
vector float result;
vector float hi, lo;
vector float bias;
/* Break in the input x into two parts ceil(x), x - ceil(x).
*/
bias = (vector float)(spu_rlmaska((vector signed int)(x), -31));
bias = (vector float)(spu_andc(spu_splats((unsigned int)0x3F7FFFFF), (vector unsigned int)bias));
ix = spu_convts(spu_add(x, bias), 0);
frac = spu_sub(spu_convtf(ix, 0), x);
frac = spu_mul(frac, spu_splats((float)SM_LN2));
overflow = spu_rlmask(spu_cmpgt(ix, 128), -1);
underflow = spu_cmpgt(ix, -128);
exp_int = (vector float)spu_and((vector unsigned int)spu_sl(spu_add(ix, 127), 23), underflow);
/* 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).
*/
frac2 = spu_mul(frac, frac);
frac4 = spu_mul(frac2, frac2);
hi = spu_madd(frac, spu_splats(-0.0001413161f), spu_splats(0.0013298820f));
hi = spu_madd(frac, hi, spu_splats(-0.0083013598f));
hi = spu_madd(frac, hi, spu_splats(0.0416573475f));
lo = spu_madd(frac, spu_splats(-0.1666653019f), spu_splats(0.4999999206f));
lo = spu_madd(frac, lo, spu_splats(-0.9999999995f));
lo = spu_madd(frac, lo, spu_splats(1.0f));
exp_frac = spu_madd(frac4, hi, lo);
ix = spu_add(ix, spu_rlmask((vector signed int)(exp_frac), -23));
result = spu_mul(exp_frac, exp_int);
/* Handle overflow */
result = spu_or(result, (vector float)overflow);
return (result);
}
#endif /* _EXP2F4_H_ */
#endif /* __SPU__ */