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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__ */ |