Retro68/gcc/newlib/libm/machine/spu/headers/expf4.h
2012-03-27 01:51:53 +02:00

113 lines
4.4 KiB
C

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/* PROLOG END TAG zYx */
#ifdef __SPU__
#ifndef _EXPF4_H_
#define _EXPF4_H_ 1
#include "floorf4.h"
#include "ldexpf4.h"
/*
* FUNCTION
* vector float _expf4(vector float x)
*
* DESCRIPTION
* The _expf4 function computes e raised to the input x for
* each of the element of the float vector.
*
*/
static __inline vector float _expf4(vector float x)
{
// log2(e)
vec_float4 log2e = spu_splats(1.4426950408889634074f);
// Extra precision for the ln2 multiply
vec_float4 ln2_hi = spu_splats(0.693359375f);
vec_float4 ln2_lo = spu_splats(-2.12194440E-4f);
// Coefficents for the Taylor series
vec_float4 f02 = spu_splats(5.0000000000000000E-1f); // 1/2!
vec_float4 f03 = spu_splats(1.6666666666666667E-1f); // 1/3!
vec_float4 f04 = spu_splats(4.1666666666666667E-2f); // 1/4!
vec_float4 f05 = spu_splats(8.3333333333333333E-3f); // 1/5!
vec_float4 f06 = spu_splats(1.3888888888888889E-3f); // 1/6!
vec_float4 f07 = spu_splats(1.9841269841269841E-4f); // 1/7!
// Range reduce input, so that:
// e^x = e^z * 2^n
// e^x = e^z * e^(n * ln(2))
// e^x = e^(z + (n * ln(2)))
vec_int4 n; // exponent of reduction
vec_float4 q; // range reduced result
vec_float4 z;
vec_float4 r;
z = spu_madd(x,log2e,spu_splats(0.5f));
z = _floorf4(z);
r = spu_nmsub(z,ln2_hi,x);
r = spu_nmsub(z,ln2_lo,r);
n = spu_convts(z,0);
z = spu_mul(r,r);
// Use Horner's method on the Taylor series
q = spu_madd(r,f07,f06);
q = spu_madd(q,r,f05);
q = spu_madd(q,r,f04);
q = spu_madd(q,r,f03);
q = spu_madd(q,r,f02);
q = spu_madd(q,z,r);
q = spu_add(q,spu_splats(1.0f));
// Adjust the result by the range reduction
r = _ldexpf4( q, n );
return(r);
}
#endif /* _EXPF4_H_ */
#endif /* __SPU__ */