Performance comparison of unaryexpr's function on matrix elements in eigen Library

The header function used in the test

#include <chrono>
#include <iostream>
#include <Eigen/Dense>

General realization of hard limit function

/*   Symmetric hard limit function 
 *   return value : 1 if m[] > 0.0f
 *               -1 else
 */
Eigen::MatrixXf hardlims_slow(Eigen::MatrixXf m)
{
	Eigen::MatrixXf t(m.rows(), m.cols());

	for (int x = 0; x < m.rows(); x++) {
		for (int y = 0; y < m.cols(); y++) {
			t(x, y) = (m(x, y) > 0.0f) ? 1.0f : -1.0f;
		}
	}
	return t;
}

Hard limit function UnaryExpr Realization

Eigen::MatrixXf hardlims(Eigen::MatrixXf m)
{
	return m.unaryExpr([](double x) { return 2.0f*(x >= 0.0f) - 1.0f; });
}

Here is the test code snippet

	auto t1  = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
	for (int i = 0; i < 1000000; i++)
	{
		m4f_hardlim = hardlims_slow(m4f);
	}
	auto t2 = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
	auto d1 = t2-t1;
	std::cout << "duration 1 : " << d1 << std::endl;
	for (int i = 0; i < 1000000; i++)
	{
		m4f_hardlim = hardlims(m4f);
	}
	auto t3 = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
	auto d2 = t3 - t2;
	std::cout << "duration 2 : " << d2 << std::endl;

The test results are as follows

duration 1 : 24998521
duration 2 : 10431488

Generally, it takes about... To realize one million operations 25 second ,UnaryExpr Implementation time is about 10.4 second .