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Added new version of the TensorIntDiv class optimized for 32 bit signed integers. It saves 1 register on CPU and 2 on GPU.

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This commit is contained in:
Benoit Steiner 2015-05-19 13:59:52 -07:00
parent 051d5325cc
commit a81d17b73a
2 changed files with 64 additions and 2 deletions
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62
unsupported/Eigen/CXX11/src/Tensor/TensorIntDiv.h
View File

@ -87,6 +87,68 @@ struct TensorIntDivisor {
};
// Optimized version for signed 32 bit integers.
// Derived from Hacker's Delight.
template <>
class TensorIntDivisor<int> {
public:
EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE TensorIntDivisor() {
magic = 0;
shift = 0;
}
// Must have 2 <= divider
EIGEN_DEVICE_FUNC TensorIntDivisor(int divider) {
eigen_assert(divider >= 2);
calcMagic(divider);
}
EIGEN_DEVICE_FUNC EIGEN_ALWAYS_INLINE int divide(const int n) const {
#ifdef __CUDA_ARCH__
return (__umulhi(magic, n) >> shift);
#else
uint64_t v = static_cast<uint64_t>(magic) * static_cast<uint64_t>(n);
return (static_cast<unsigned int>(v >> 32) >> shift);
#endif
}
private:
// Compute the magic numbers. See Hacker's Delight section 10 for an in
// depth explanation.
EIGEN_DEVICE_FUNC void calcMagic(int d) {
const unsigned two31 = 0x80000000; // 2**31.
unsigned ad = d;
unsigned t = two31 + (ad >> 31);
unsigned anc = t - 1 - t%ad; // Absolute value of nc.
int p = 31; // Init. p.
unsigned q1 = two31/anc; // Init. q1 = 2**p/|nc|.
unsigned r1 = two31 - q1*anc; // Init. r1 = rem(2**p, |nc|).
unsigned q2 = two31/ad; // Init. q2 = 2**p/|d|.
unsigned r2 = two31 - q2*ad; // Init. r2 = rem(2**p, |d|).
unsigned delta = 0;
do {
p = p + 1;
q1 = 2*q1; // Update q1 = 2**p/|nc|.
r1 = 2*r1; // Update r1 = rem(2**p, |nc|).
if (r1 >= anc) { // (Must be an unsigned
q1 = q1 + 1; // comparison here).
r1 = r1 - anc;}
q2 = 2*q2; // Update q2 = 2**p/|d|.
r2 = 2*r2; // Update r2 = rem(2**p, |d|).
if (r2 >= ad) { // (Must be an unsigned
q2 = q2 + 1; // comparison here).
r2 = r2 - ad;}
delta = ad - r2;
} while (q1 < delta || (q1 == delta && r1 == 0));
magic = (unsigned)(q2 + 1);
shift = p - 32;
}
unsigned int magic;
int shift;
};
template <typename T>
static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE T operator / (const T& numerator, const TensorIntDivisor<T>& divisor) {
return divisor.divide(numerator);

4
unsupported/test/cxx11_tensor_intdiv.cpp
View File

@ -1,7 +1,7 @@
// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2014 Benoit Steiner <benoit.steiner.goog@gmail.com>
// Copyright (C) 2014-2015 Benoit Steiner <benoit.steiner.goog@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
@ -14,7 +14,7 @@
void test_signed_32bit()
{
for (int32_t i = 1; i < 25000; ++i) {
for (int32_t i = 2; i < 25000; ++i) {
const Eigen::internal::TensorIntDivisor<int32_t> div(i);
for (int32_t j = 0; j < 25000; ++j) {