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Improve polynomial evaluation with instruction-level parallelism for pexp_float and pexp<Packet16f>

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This commit is contained in:
guoqiangqi 2020-10-20 11:37:09 +08:00
parent 4a77eda1fd
commit 28aef8e816
2 changed files with 21 additions and 21 deletions
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20
Eigen/src/Core/arch/AVX512/MathFunctions.h
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@ -85,17 +85,17 @@ pexp<Packet16f>(const Packet16f& _x) {
_EIGEN_DECLARE_CONST_Packet16f(nln2, -0.6931471805599453f);
Packet16f r = _mm512_fmadd_ps(m, p16f_nln2, x);
Packet16f r2 = pmul(r, r);
Packet16f r3 = pmul(r2, r);
// TODO(gonnet): Split into odd/even polynomials and try to exploit
// instruction-level parallelism.
Packet16f y = p16f_cephes_exp_p0;
y = pmadd(y, r, p16f_cephes_exp_p1);
y = pmadd(y, r, p16f_cephes_exp_p2);
y = pmadd(y, r, p16f_cephes_exp_p3);
y = pmadd(y, r, p16f_cephes_exp_p4);
y = pmadd(y, r, p16f_cephes_exp_p5);
y = pmadd(y, r2, r);
y = padd(y, p16f_1);
// Evaluate the polynomial approximant,improved by instruction-level parallelism.
Packet16f y, y1, y2;
y = pmadd(p16f_cephes_exp_p0, r, p16f_cephes_exp_p1);
y1 = pmadd(p16f_cephes_exp_p3, r, p16f_cephes_exp_p4);
y2 = padd(r, p16f_1);
y = pmadd(y, r, p16f_cephes_exp_p2);
y1 = pmadd(y1, r, p16f_cephes_exp_p5);
y = pmadd(y, r3, y1);
y = pmadd(y, r2, y2);
// Build emm0 = 2^m.
Packet16i emm0 = _mm512_cvttps_epi32(padd(m, p16f_127));

22
Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
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@ -345,18 +345,18 @@ Packet pexp_float(const Packet _x)
#endif
Packet r2 = pmul(r, r);
Packet r3 = pmul(r2, r);
// TODO(gonnet): Split into odd/even polynomials and try to exploit
// instruction-level parallelism.
Packet y = cst_cephes_exp_p0;
y = pmadd(y, r, cst_cephes_exp_p1);
y = pmadd(y, r, cst_cephes_exp_p2);
y = pmadd(y, r, cst_cephes_exp_p3);
y = pmadd(y, r, cst_cephes_exp_p4);
y = pmadd(y, r, cst_cephes_exp_p5);
y = pmadd(y, r2, r);
y = padd(y, cst_1);
// Evaluate the polynomial approximant,improved by instruction-level parallelism.
Packet y, y1, y2;
y = pmadd(cst_cephes_exp_p0, r, cst_cephes_exp_p1);
y1 = pmadd(cst_cephes_exp_p3, r, cst_cephes_exp_p4);
y2 = padd(r, cst_1);
y = pmadd(y, r, cst_cephes_exp_p2);
y1 = pmadd(y1, r, cst_cephes_exp_p5);
y = pmadd(y, r3, y1);
y = pmadd(y, r2, y2);
// Return 2^m * exp(r).
return pmax(pldexp(y,m), _x);
}