[Comparing floats Knuth]

compareFloats.cpp

#include <cmath>
// return true if the difference between a and b is less than absEpsilon (a very small number, e.g. 1e-12), or within relEpsilon percent of the larger of a and b
bool approximatelyEqualAbsRel(double a, double b, double absEpsilon, double relEpsilon)
{
    // Check if the numbers are really close -- needed when comparing numbers near zero.
    double diff = fabs(a - b);
    if (diff <= absEpsilon)
        return true;
 
    // Otherwise fall back to Knuth's algorithm
    return diff <= ( (fabs(a) < fabs(b) ? fabs(b) : fabs(a)) * relEpsilon);
}

Hi @thm-development,

The absEpsilon and relEpsilon values depend on the level of precision that you need for your purposes. If

absEpsilon is 1e-3 relEpsilon is 1e-6

seem to work for your use case, I would go with them.

I want to mention that this code snippet is an excerpt from a website that I consider one of the best resources in C++ on the web. The algorithm and logic behind it is explained there.

Hope this helps. If you have any other questions, please do.

Hello,
thank you very much for your answer.
I have read the post on LearnCpp site and the author uses 1e-12 for the absEpsilon and 1e-8 for the relEpsilon !
I'll try this and analyse the results. Maybe it's a good idea to use an absEpsilon smaller than the relEpsilon.
Thanks again for your answer.
Best reagrds

@tdm-development, you are very welcome! Good luck!