Comparing floating point number to zero

Question

The C++ FAQ lite \"[29.17] Why doesn\'t my floating-point comparison work?\" recommends this equality test:

#include   /* for std::abs(double) *         


        

Answer 1

notice, that code is:

std::abs((x - y)/x) <= epsilon

you are requiring that the "relative error" on the var is <= epsilon, not that the absolute difference is