// Copyright (C) 2010, Guy Barrand. All rights reserved.
// See the file tools.license for terms.

#ifndef tools_rtausmeui
#define tools_rtausmeui

// G.Barrand : not so clear if 0 and tools::uint32_max() are included.
//             A simple program shows that "if(r.shoot()==tools::uint32_max())" shows hits.
//             (But we did not see hits for "if(r.shoot()==0)"). (See tools/tests/rand.cpp).

// tausme is for Tausworthe maxmally equidistributed.

// From logic and code of CERN-ROOT/TRandom2 class.

// Random number generator class based on the maximally quidistributed combined
// Tausworthe generator by L'Ecuyer.
//
// The period of the generator is 2**88 (about 10**26) and it uses only 3 words
// for the state.
//
// For more information see:
// P. L'Ecuyer, Mathematics of Computation, 65, 213 (1996)
// P. L'Ecuyer, Mathematics of Computation, 68, 225 (1999)
//
// The publication are available online at
//  http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
//  http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps

namespace tools {

class rtausmeui {
public:
  rtausmeui(unsigned int a_seed = 1):m_seed(0),m_seed1(0),m_seed2(0){
    set_seed(a_seed);
  }
  virtual ~rtausmeui(){
  }
public:
  rtausmeui(const rtausmeui& a_from):m_seed(a_from.m_seed),m_seed1(a_from.m_seed1),m_seed2(a_from.m_seed2){
  }
  rtausmeui& operator=(const rtausmeui& a_from) {
    m_seed = a_from.m_seed;
    m_seed1 = a_from.m_seed1;
    m_seed2 = a_from.m_seed2;
    return *this;
  }
public:
  void set_seed(unsigned int a_seed) {
    m_seed = a_seed?a_seed:1;

    // Generate m_seed[1,2] needed for the generator state using
    // a linear congruential generator
    // The only condition, stated at the end of the 1999 L'Ecuyer paper is that the seeds
    // must be greater than 1,7 and 15.

    m_seed = LCG(m_seed);
    if (m_seed < 2) m_seed += 2UL;
    m_seed1 = LCG(m_seed);
    if (m_seed1 < 8) m_seed1 += 8UL;
    m_seed2 = LCG(m_seed1);
    if (m_seed2 < 16) m_seed2 += 16UL;

    // "warm it up" by calling it 6 times
    for (unsigned int i = 0; i < 6; ++i) shoot();
  }
  unsigned int seed() const {return m_seed;}

  unsigned int shoot() {
    //  TausWorth generator from L'Ecuyer, uses as seed 3x32bits integers
    //  Use a mask of 0xffffffffUL to make in work on 64 bit machines
    //  Periodicity of about  10**26

    unsigned int y;

    do {
      m_seed  = TAUSWORTHE (m_seed, 13, 19, 4294967294UL, 12);
      m_seed1 = TAUSWORTHE (m_seed1, 2, 25, 4294967288UL, 4);
      m_seed2 = TAUSWORTHE (m_seed2, 3, 11, 4294967280UL, 17);

      y = m_seed ^ m_seed1 ^ m_seed2;
    } while(!y);

    return y;
  }
protected:
  static unsigned int LCG(unsigned int a_n) {
    return ((69069 * a_n) & 0xffffffffUL);  // linear congurential generator
  }
  static unsigned int TAUSWORTHE(unsigned int a_s,unsigned int a_a,unsigned int a_b,unsigned int a_c,unsigned int a_d) {
    return (((a_s & a_c) << a_d) & 0xffffffffUL ) ^ ((((a_s << a_a) & 0xffffffffUL )^ a_s) >> a_b);
  }
protected:
  unsigned int m_seed;
  unsigned int m_seed1;
  unsigned int m_seed2;
};

}

#endif
