// Random number generator, adapted from HP STL code.

/* Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 */

#ifndef RNG_H
#define RNG_H


class rng
{
private:
  unsigned long table[55];
  size_t index1;
  size_t index2;
public:
  rng(unsigned long s=0) { seed(s); }
  unsigned long operator()(unsigned long limit)
  {
    index1 = (index1 + 1) % 55;
    index2 = (index2 + 1) % 55;
    table[index1] = table[index1] - table[index2];
    return table[index1] % limit;
  }
  void seed(unsigned long s);
};

void rng::seed(unsigned long s) 
{
  unsigned long k = 1;
  table[54] = s;
  for (size_t i = 0; i < 54; i++) 
  {
    size_t ii = 21 * i % 55;
    table[ii] = k;
    k = s - k;
    s = table[ii];
  }
  for (int loop = 0; loop < 4; loop++) 
  {
    for (i = 0; i < 55; i++)
      table[i] = table[i] - table[(1 + i + 30) % 55];
  }
  index1 = 0;
  index2 = 31;
};


#endif