random.hpp

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/* -*- mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- */
/*
 *  Main authors:
 *     Christian Schulte <schulte@gecode.org>
 *     Mikael Lagerkvist <lagerkvist@gecode.org>
 *
 *  Copyright:
 *     Christian Schulte, 2005
 *     Mikael Lagerkvist, 2005
 *
 *  Last modified:
 *     $Date: 2011-05-11 12:44:17 +0200 (Wed, 11 May 2011) $ by $Author: tack $
 *     $Revision: 12001 $
 *
 *  This file is part of Gecode, the generic constraint
 *  development environment:
 *     http://www.gecode.org
 *
 *  Permission is hereby granted, free of charge, to any person obtaining
 *  a copy of this software and associated documentation files (the
 *  "Software"), to deal in the Software without restriction, including
 *  without limitation the rights to use, copy, modify, merge, publish,
 *  distribute, sublicense, and/or sell copies of the Software, and to
 *  permit persons to whom the Software is furnished to do so, subject to
 *  the following conditions:
 *
 *  The above copyright notice and this permission notice shall be
 *  included in all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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 */

namespace Gecode { namespace Support {

  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  class LinearCongruentialGenerator {
  private:
    static const unsigned int max = 1UL<<31;
    unsigned int s;
    unsigned int next(void);
  public:
    void seed(unsigned int _s);
    LinearCongruentialGenerator(unsigned int _s = 1);
    unsigned int seed(void) const;
    unsigned int operator ()(unsigned int n);
    size_t size(void) const;
  };

  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  forceinline unsigned int
  LinearCongruentialGenerator<m,a,q,r>::next(void) {
    s = a*(s%q) - r*(s/q);
    unsigned int res = s;
    if (s==0) s = 1;
    return res;
  }
  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  forceinline void
  LinearCongruentialGenerator<m,a,q,r>::seed(unsigned int _s) {
    s = _s % m;
    if (s == 0) s = 1;
  }
  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  forceinline
  LinearCongruentialGenerator<m,a,q,r>::
  LinearCongruentialGenerator(unsigned int _s) {
    seed(_s);
  }
  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  forceinline unsigned int
  LinearCongruentialGenerator<m,a,q,r>::seed(void) const {
    return s;
  }
  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  forceinline unsigned int
  LinearCongruentialGenerator<m,a,q,r>::operator ()(unsigned int n) {
    unsigned int x1 = next() & ((1<<16)-1);
    unsigned int x2 = next() & ((1<<16)-1);
    if (n < 2) return 0;
    double d = static_cast<double>(((x1<<16) | x2) % max) / max;
    unsigned int val = static_cast<unsigned int>(n * d);
    return (val < n) ? val : (n-1);
  }
  template<unsigned int m, unsigned int a, unsigned int q, unsigned int r>
  forceinline size_t
  LinearCongruentialGenerator<m,a,q,r>::size(void) const {
    return sizeof(LinearCongruentialGenerator<m,a,q,r>);
  }


  typedef LinearCongruentialGenerator<2147483647, 48271, 44488, 3399>
  RandomGenerator;

}}

// STATISTICS: support-any