Computes epsilon - the smallest value such that, when added to 1, is still distinguishable from 1.

main.cpp

#include <iostream>
#include <limits>
#include <cassert>

namespace std {   }
using namespace std;

/* Computes the smallest value such that, when added to 1, is still distinguishable from 1. */
template<typename T>
int epsilon(T& eps)
{
   int pow = 0;
   eps = 1;
   while (eps + 1 != 1)
   {
      eps /= 2;
      --pow;
   }

   eps *= 2;

   return pow + 1;
}

int main()
{
   float feps = 0.0f;
   double deps = 0.0;

   int feps_2pow = epsilon<float>(feps);
   int deps_2pow = epsilon<double>(deps);

   cout << "Epsilon for float:  2^" << feps_2pow << " (" << feps << ")" << endl;
   cout << "Epsilon for double: 2^" << deps_2pow << " (" << deps << ")" << endl;

   assert(numeric_limits<float>::epsilon() == feps);
   assert(numeric_limits<double>::epsilon() == deps);

   cin.get();

   return 0;
}