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Speed up exp(x).

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This commit is contained in:
Rasmus Munk Larsen
2024-11-19 17:50:34 +00:00
parent 93ec5450cb
commit 8ee6f8475a
5 changed files with 66 additions and 18 deletions
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20
Eigen/src/Core/arch/SSE/PacketMath.h
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@@ -217,7 +217,6 @@ struct packet_traits<double> : default_packet_traits {
HasCos = EIGEN_FAST_MATH,
HasTanh = EIGEN_FAST_MATH,
HasLog = 1,
HasErf = EIGEN_FAST_MATH,
HasErfc = EIGEN_FAST_MATH,
HasExp = 1,
HasSqrt = 1,
@@ -1767,7 +1766,6 @@ EIGEN_STRONG_INLINE Packet4f pldexp<Packet4f>(const Packet4f& a, const Packet4f&
// We specialize pldexp here, since the generic implementation uses Packet2l, which is not well
// supported by SSE, and has more range than is needed for exponents.
// TODO(rmlarsen): Remove this specialization once Packet2l has support or casting.
template <>
EIGEN_STRONG_INLINE Packet2d pldexp<Packet2d>(const Packet2d& a, const Packet2d& exponent) {
// Clamp exponent to [-2099, 2099]
@@ -1788,6 +1786,24 @@ EIGEN_STRONG_INLINE Packet2d pldexp<Packet2d>(const Packet2d& a, const Packet2d&
return out;
}
// We specialize pldexp here, since the generic implementation uses Packet2l, which is not well
// supported by SSE, and has more range than is needed for exponents.
template <>
EIGEN_STRONG_INLINE Packet2d pldexp_fast<Packet2d>(const Packet2d& a, const Packet2d& exponent) {
// Clamp exponent to [-1023, 1024]
const Packet2d min_exponent = pset1<Packet2d>(-1023.0);
const Packet2d max_exponent = pset1<Packet2d>(1024.0);
const Packet2d e = pmin(pmax(exponent, min_exponent), max_exponent);
// Convert e to integer and swizzle to low-order bits.
const Packet4i ei = vec4i_swizzle1(_mm_cvtpd_epi32(e), 0, 3, 1, 3);
// Compute 2^e multiply:
const Packet4i bias = _mm_set_epi32(0, 1023, 0, 1023);
const Packet2d c = _mm_castsi128_pd(_mm_slli_epi64(padd(ei, bias), 52)); // 2^e
return pmul(a, c);
}
// with AVX, the default implementations based on pload1 are faster
#ifndef __AVX__
template <>