Retro68/gcc/newlib/libm/machine/spu/headers/tanhf4.h
2012-03-27 01:51:53 +02:00

136 lines
4.9 KiB
C

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/* PROLOG END TAG zYx */
#ifdef __SPU__
#ifndef _TANHF4_H_
#define _TANHF4_H_ 1
#include <spu_intrinsics.h>
#include "expf4.h"
#include "divf4.h"
#include "tanhd2.h"
/*
* FUNCTION
* vector float _tanhf4(vector float x)
*
* DESCRIPTION
* The _tanhf4 function computes the hyperbolic tangent for each
* element of the input vector.
*
* We use the following to approximate tanh:
*
* |x| <= .25: Taylor Series
* |x| > .25: tanh(x) = (exp(2x) - 1)/(exp(2x) + 1)
*
*
* SPECIAL CASES:
* - tanh(+/- 0) = +/-0
* - tanh(+/- infinity) = +/- 1
*
*/
static __inline vector float _tanhf4(vector float x)
{
vector float signbit = spu_splats(-0.0f);
vector float onef = spu_splats(1.0f);
vector float twof = spu_splats(2.0f);
vector float xabs;
vector float x2;
vector unsigned int gttaylor;
vector float e;
vector float tresult;
vector float eresult;
vector float result;
xabs = spu_andc(x, signbit);
/*
* This is where we switch from Taylor Series
* to exponential formula.
*/
gttaylor = spu_cmpgt(xabs, spu_splats(0.25f));
/*
* Taylor Series Approximation
*/
x2 = spu_mul(x,x);
tresult = spu_madd(x2, spu_splats((float)TANH_TAY06), spu_splats((float)TANH_TAY05));
tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY04));
tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY03));
tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY02));
tresult = spu_madd(x2, tresult, spu_splats((float)TANH_TAY01));
tresult = spu_mul(xabs, tresult);
/*
* Exponential Formula
* Our expf4 function gives a more accurate result in general
* with xabs instead of x for x<0. We correct for sign later.
*/
e = _expf4(spu_mul(xabs, twof));
eresult = _divf4(spu_sub(e, onef), spu_add(e, onef));
/*
* Select Taylor or exp result.
*/
result = spu_sel(tresult, eresult, gttaylor);
/*
* Correct for accumulated truncation error when
* tanh(x) should return 1.
* Note that this also handles the special case of
* x = +/- infinity.
*/
result = spu_sel(result, onef, spu_cmpgt(xabs, spu_splats(9.125f)));
/*
* Antisymmetric function - preserve sign bit of x
* in the result.
*/
result = spu_sel(result, x, (vec_uint4)signbit);
return result;
}
#endif /* _TANHF4_H_ */
#endif /* __SPU__ */