EigenDX.cpp

// Compiled with VS 2022: Release AMD64, AVX2 ISA, LTCG
// RDTSC time on Ryzen 7 8700G for 1024 matrices: 15834 Eigen, 7224 DirectXMath
constexpr bool useEigen = true;

// Eigen 3.4.0
#include <Eigen/Eigen>
__forceinline void multiplyWithEigen( float* rdi, const float* rsi )
{
	using Mat = Eigen::Matrix<float, 4, 4, Eigen::RowMajor>;
	static_assert( sizeof( Mat ) == 4 * 4 * sizeof( float ) );

	const Mat& lhs = *(const Mat*)( rsi );
	const Mat& rhs = *(const Mat*)( rsi + 16 );
	Mat& prod = *(Mat*)rdi;

	prod.noalias() = lhs * rhs;
}

// DirectXMath current master
#include "DirectXMath/DirectXMath.h"
__forceinline void multiplyWithDxMath( float* rdi, const float* rsi )
{
	using namespace DirectX;
	XMMATRIX lhs = XMLoadFloat4x4( (const XMFLOAT4X4*)( rsi ) );
	XMMATRIX rhs = XMLoadFloat4x4( (const XMFLOAT4X4*)( rsi + 16 ) );
	XMMATRIX prod = XMMatrixMultiply( lhs, rhs );
	XMStoreFloat4x4( (XMFLOAT4X4*)rdi, prod );
}

static void __declspec( noinline ) multiplyMatrices( float* rdi, size_t count, const float* rsi )
{
	const float* const rsiEnd = rsi + count * ( 16 * 2 );
	for( ; rsi < rsiEnd; rsi += ( 16 * 2 ), rdi += 16 )
	{
		if constexpr( useEigen )
			multiplyWithEigen( rdi, rsi );
		else
			multiplyWithDxMath( rdi, rsi );
	}
}

#include <vector>
#include <random>
// Generate FP32 vector filled with [ -1 .. +1 ] random values
std::vector<float> makeRandomVector( size_t length )
{
	std::vector<float> vec( length );
	std::random_device rd; // Seed
	std::mt19937 gen( rd() ); // Mersenne Twister RNG
	std::uniform_real_distribution<float> dis( -1.0f, 1.0f ); // Range [-1, +1]
	for( float& value : vec )
		value = dis( gen );
	return vec;
}

#include <stdio.h>
int main()
{
	constexpr size_t countMatrices = 1024;

	const std::vector<float> source = makeRandomVector( 4 * 4 * 2 * countMatrices );
	std::vector<float> result;
	result.resize( 4 * 4 * countMatrices );

	const uint64_t start = __rdtsc();
	_ReadBarrier();

	multiplyMatrices( result.data(), countMatrices, source.data() );

	_ReadBarrier();
	const uint64_t end = __rdtsc();

	printf( "%lli cycles; %g\n", end - start, *result.rbegin() );
	return 0;
}