A small random number generator.

main.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <cassert>

#define SAMPLE_SIZE 36000

namespace std {   }
using namespace std;

struct RandomNumberGenerator
{
// Marsaglia MWC generator
// http://en.wikipedia.org/wiki/Talk:Random_number_generation#Marsaglia_MWC_generator
   RandomNumberGenerator() : m_z(0x74826158), m_w(0x36187008) {   }
   RandomNumberGenerator(unsigned int z, unsigned int w) : m_z(z), m_w(w) {   }

   unsigned int GetUINT()
   {
       m_z = 36969 * (m_z & 65535) + (m_z >> 16);
       m_w = 18000 * (m_w & 65535) + (m_w >> 16);

       return (m_z << 16) + m_w; // 0 <= u < 2^32
   }

   double GetNext()
   {
   // The magic number below is 1 / (2 ^ 32 + 2).
   // The result is strictly between 0 and 1.
      return (GetUINT() + 1.0) * 2.328306435454494e-10;
   }

   private:
   unsigned int m_z, m_w;
};

int main(int argc, char* argv[])
{
   RandomNumberGenerator rng;
   bool failed = false;

   vector<double> store(SAMPLE_SIZE);

   for (size_t i = 0; i < SAMPLE_SIZE && failed == false; ++i)
   {
      double r = rng.GetNext();

      if (store.end() != find(store.begin(), store.end(), r))
      {
         cout << "Test failed. Duplicate found." << endl;
         failed = true;
      }
      else
      {
         store[i] = r;
      }
   }

   assert(failed == false);

   if (failed == false)
   {
      cout << "Test passed." << endl;
   }

   cin.get();

  return 0;
}