Machine Epsilon 的作用

epsilon.cc

#include <limits>
#include <iostream>

int main() {
    float eps = std::numeric_limits<float>::epsilon();
    float a = 1.0f;
    float b = a + eps;
    float c = a + eps / 2.0f;
    std::cout << "a == b: " << std::boolalpha << (a == b) << "\n";  // false
    std::cout << "a == c: " << std::boolalpha << (a == c) << "\n";  // true
    return 0;
}

如何自己获得 Machine Epsilon？

In [1]: 7./3 - 4./3 -1
Out[1]: 2.220446049250313e-16

参考：https://stackoverflow.com/a/25155518/8102500