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Optimized implementation of the hyperbolic tangent function for AVX

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This commit is contained in:
Benoit Steiner 2016-02-10 08:48:05 -08:00
parent e6ee18d6b4
commit 2d523332b3
2 changed files with 54 additions and 0 deletions
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53
Eigen/src/Core/arch/AVX/MathFunctions.h
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@ -265,6 +265,59 @@ pexp<Packet8f>(const Packet8f& _x) {
return pmax(pmul(y, _mm256_castsi256_ps(emm0)), _x);
}
// Hyperbolic Tangent function.
// Doesn't do anything fancy, just a 13/6-degree rational interpolant which
// is accurate up to a couple of ulp in the range [-8, 8], outside of which the
// fl(tanh(x)) = +/-1.
template <>
EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet8f
ptanh<Packet8f>(const Packet8f& _x) {
// Map the range [-8, 8] to [-1, 1], we will clamp bad coefficients later.
const Packet8f x = _mm256_mul_ps(_x, _mm256_set1_ps(0.125f));
// The monomial coefficients of the numerator polynomial (odd).
_EIGEN_DECLARE_CONST_Packet8f(alpha_1, -2.47030171958948e-03);
_EIGEN_DECLARE_CONST_Packet8f(alpha_3, -2.06804010015822e-02);
_EIGEN_DECLARE_CONST_Packet8f(alpha_5, -3.13693994587418e-02);
_EIGEN_DECLARE_CONST_Packet8f(alpha_7, -7.19851201683627e-03);
_EIGEN_DECLARE_CONST_Packet8f(alpha_9, 8.31561269687160e-04);
_EIGEN_DECLARE_CONST_Packet8f(alpha_11, -1.37626659546502e-04);
_EIGEN_DECLARE_CONST_Packet8f(alpha_13, 1.39116714700458e-05);
// The monomial coefficients of the denominator polynomial (even).
_EIGEN_DECLARE_CONST_Packet8f(beta_0, -3.08787724141615e-04);
_EIGEN_DECLARE_CONST_Packet8f(beta_2, -9.17251911622436e-03);
_EIGEN_DECLARE_CONST_Packet8f(beta_4, -3.09625062090444e-02);
_EIGEN_DECLARE_CONST_Packet8f(beta_6, -2.05669680763032e-02);
// Since the polynomials are odd/even, we need x^2.
const Packet8f x2 = _mm256_mul_ps(x, x);
// Evaluate the numerator polynomial p.
Packet8f p = pmadd(x2, p8f_alpha_13, p8f_alpha_11);
p = pmadd(x2, p, p8f_alpha_9);
p = pmadd(x2, p, p8f_alpha_7);
p = pmadd(x2, p, p8f_alpha_5);
p = pmadd(x2, p, p8f_alpha_3);
p = pmadd(x2, p, p8f_alpha_1);
p = pmul(x, p);
// Evaluate the denominator polynomial p.
Packet8f q = pmadd(x2, p8f_beta_6, p8f_beta_4);
q = pmadd(x2, q, p8f_beta_2);
q = pmadd(x2, q, p8f_beta_0);
// Divide the numerator by the denominator.
const Packet8f res = pdiv(p, q);
// Mask-out values outside of [-8, 8].
_EIGEN_DECLARE_CONST_Packet8f(one, 1.0f);
_EIGEN_DECLARE_CONST_Packet8f(minus_one, -1.0f);
return _mm256_blendv_ps(
_mm256_blendv_ps(res, p8f_one, _mm256_cmp_ps(x, p8f_one, _CMP_GT_OQ)),
p8f_minus_one, _mm256_cmp_ps(x, p8f_minus_one, _CMP_LT_OQ));
}
template <>
EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet4d
pexp<Packet4d>(const Packet4d& _x) {

1
Eigen/src/Core/arch/AVX/PacketMath.h
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@ -66,6 +66,7 @@ template<> struct packet_traits<float> : default_packet_traits
HasExp = 1,
HasSqrt = 1,
HasRsqrt = 1,
HasTanh = EIGEN_FAST_MATH,
HasBlend = 1,
HasRound = 1,
HasFloor = 1,