Compare double to zero using epsilon

Question

Today, I was looking through some C++ code (written by somebody else) and found this section:

double someValue = ...
if (someValue <  std::numeric_limits&         


        

Answer 1

There are numbers that exist between 0 and epsilon because epsilon is the difference between 1 and the next highest number that can be represented above 1 and not the difference between 0 and the next highest number that can be represented above 0 (if it were, that code would do very little):-

#include 

int main ()
{
  struct Doubles
  {
      double one;
      double epsilon;
      double half_epsilon;
  } values;

  values.one = 1.0;
  values.epsilon = std::numeric_limits::epsilon();
  values.half_epsilon = values.epsilon / 2.0;
}

Using a debugger, stop the program at the end of main and look at the results and you'll see that epsilon / 2 is distinct from epsilon, zero and one.

So this function takes values between +/- epsilon and makes them zero.