diff options
author | Benoit Steiner <benoit.steiner.goog@gmail.com> | 2016-02-10 08:48:05 -0800 |
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committer | Benoit Steiner <benoit.steiner.goog@gmail.com> | 2016-02-10 08:48:05 -0800 |
commit | 2d523332b397af4dc01d648605ff677cef2ed1f0 (patch) | |
tree | fdd4cfe85e304c399ca3b6b7988760991bb7398d /Eigen/src/Core | |
parent | e6ee18d6b46229b0028c454db5f389001649bd45 (diff) |
Optimized implementation of the hyperbolic tangent function for AVX
Diffstat (limited to 'Eigen/src/Core')
-rw-r--r-- | Eigen/src/Core/arch/AVX/MathFunctions.h | 53 | ||||
-rw-r--r-- | Eigen/src/Core/arch/AVX/PacketMath.h | 1 |
2 files changed, 54 insertions, 0 deletions
diff --git a/Eigen/src/Core/arch/AVX/MathFunctions.h b/Eigen/src/Core/arch/AVX/MathFunctions.h index b0e0222a4..3ea38ae07 100644 --- a/Eigen/src/Core/arch/AVX/MathFunctions.h +++ b/Eigen/src/Core/arch/AVX/MathFunctions.h @@ -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) { diff --git a/Eigen/src/Core/arch/AVX/PacketMath.h b/Eigen/src/Core/arch/AVX/PacketMath.h index 717ae67c5..4fec14f44 100644 --- a/Eigen/src/Core/arch/AVX/PacketMath.h +++ b/Eigen/src/Core/arch/AVX/PacketMath.h @@ -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, |