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Provide a more efficient Packet2l->Packet2d cast method

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This commit is contained in:
Christoph Hertzberg 2020-09-27 23:02:34 +02:00
parent 6425e875a1
commit 6b0c0b587e
1 changed files with 22 additions and 15 deletions
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37
Eigen/src/Core/arch/SSE/TypeCasting.h
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@ -82,21 +82,6 @@ template<> EIGEN_STRONG_INLINE Packet2l pcast<Packet2d, Packet2l>(const Packet2d
#endif
}
template <>
EIGEN_STRONG_INLINE Packet2d pcast<Packet2l, Packet2d>(const Packet2l& a) {
#ifdef EIGEN_VECTORIZE_SSE4_1
int64_t a0 = _mm_extract_epi64(a, 0);
int64_t a1 = _mm_extract_epi64(a, 1);
#elif EIGEN_ARCH_x86_64
int64_t a0 = _mm_cvtsi128_si64(a);
int64_t a1 = _mm_cvtsi128_si64(_mm_unpackhi_epi64(a, a));
#else
int64_t a0 = a.m_val[0];
int64_t a1 = a.m_val[1];
#endif
return _mm_set_pd(static_cast<double>(a1), static_cast<double>(a0));
}
template<> EIGEN_STRONG_INLINE Packet4i preinterpret<Packet4i,Packet4f>(const Packet4f& a) {
return _mm_castps_si128(a);
}
@ -113,6 +98,28 @@ template<> EIGEN_STRONG_INLINE Packet2d preinterpret<Packet2d, Packet2l>(const P
return _mm_castsi128_pd(a);
}
template <>
EIGEN_STRONG_INLINE Packet2d pcast<Packet2l, Packet2d>(const Packet2l& a) {
#ifdef EIGEN_VECTORIZE_AVX512DQ
// AVX512DQ finally provides an instruction for this
return _mm_cvtepi64_pd(a);
#else
// Before AVX512, there is no packed epi64 to double cast instruction
// The idea is to convert upper and lower half separately, via bit-twiddling
// then add them together, but remove the offsets
Packet2d upper = preinterpret<Packet2d>(plogical_shift_right<32>(a));
Packet2d lower = pand(pset1frombits<Packet2d>(0xffffffffUL), preinterpret<Packet2d>(a));
// upper = 2**(53+32) + ((a >> 32) + 0x80000000)
upper = pxor(pset1frombits<Packet2d>(0x4530000080000000UL), upper); // exponent of 52+32, and xor the upper bit of 32bit mantissa
// lower = 2**53 + (a & 0xffffffff)
lower = pxor(pset1frombits<Packet2d>(0x4330000000000000UL), lower); // exponent of 52
// adding upper+lower would be 2**84+2**63+2**52 too big. Create the negative of that:
Packet2d offset = pset1frombits<Packet2d>(0xC530000080100000UL);
// add everything together, start with the bigger numbers, since the 2**84 will cancel out, giving an exact result
return padd(padd(offset, upper), lower);
#endif
}
// Disable the following code since it's broken on too many platforms / compilers.
//#elif defined(EIGEN_VECTORIZE_SSE) && (!EIGEN_ARCH_x86_64) && (!EIGEN_COMP_MSVC)
#if 0