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shuffledrand.h

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#ifndef __SHUFFLEDRAND_H__
#define __SHUFFLEDRAND_H__

#include <cassert>
#include <cmath>
#include <stdlib.h>

#ifdef ANSI_COMPATIBLE
#define NO_RAND48_AVAIL
#endif



template<class T>
class ShuffledRandom {
public:
  
  static void reset() {
    for (int i=1; i<=197; i++) v[i]= plain_rand();
    y = plain_rand();
    is_initialized = true;
  }

  static T next() {
    if (!is_initialized) reset();
    int i = (int)floor(1.0 + 197.0 * y); /* Compute a random index into v */
    assert(!(i > 197 || i < 1));
    y = v[i];                            /* Pick the number at the index  */
    v[i] = plain_rand();                    /* Restock with new random number*/
    return(y);
  }

  static int default_seed;

  static T plain_rand();

  static void plain_rand_seed(long int seedval);

private:
  static T y;
  static T v[198];
  static bool is_initialized;

  ShuffledRandom() {};
};


template<class T> T    ShuffledRandom<T>::y;
template<class T> T    ShuffledRandom<T>::v[198];
template<class T> bool ShuffledRandom<T>::is_initialized=false;
template<class T> int  ShuffledRandom<T>::default_seed=87654321;


template<class T> T
ShuffledRandom<T>::plain_rand()
{
#ifdef NO_RAND48_AVAIL

  return (rand()/(RAND_MAX+1.0));
#else
  return drand48();
#endif
}



template<class T> void
ShuffledRandom<T>::plain_rand_seed(long int seedval)
{
#ifdef NO_RAND48_AVAIL
  /* Should match the definition of plain_rand() */
  srand(seedval);
#else
  srand48(seedval);
#endif
}



inline double shuffled_rand()
{  return ShuffledRandom<double>::next();  }


inline void   shuffled_rand_reset(long int new_seed=ShuffledRandom<double>::default_seed)
{
  ShuffledRandom<double>::plain_rand_seed(new_seed);
  ShuffledRandom<double>::reset();
  ShuffledRandom<double>::next();
}


#endif /* __SHUFFLEDRAND_H__ */

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