minisat_varorder.h

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/*****************************************************************************/
/*!
 *\file minisat_varorder.h
 *\brief MiniSat decision heuristics
 *
 * Author: Alexander Fuchs
 *
 * Created: Fri Sep 08 11:04:00 2006
 *
 * <hr>
 *
 * License to use, copy, modify, sell and/or distribute this software
 * and its documentation for any purpose is hereby granted without
 * royalty, subject to the terms and conditions defined in the \ref
 * LICENSE file provided with this distribution.
 * 
 * <hr>
 */
/*****************************************************************************/

/**************************************************************************************[VarOrder.h]
MiniSat -- Copyright (c) 2003-2005, Niklas Een, Niklas Sorensson

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**************************************************************************************************/

#ifndef _cvc3__minisat__varorder_h_
#define _cvc3__minisat__varorder_h_

//=================================================================================================

#include "minisat_types.h"
#include "minisat_heap.h"
#include <iostream>
#include <vector>

// implements the decision heuristics by using a heap over variable ids (which are ints)

namespace MiniSat {

struct VarOrder_lt {
  const std::vector<double>&  activity;
  bool operator () (Var x, Var y) { return activity[x] > activity[y]; }
  VarOrder_lt(const std::vector<double>&  act) : activity(act) { }
};

class VarOrder {
  const std::vector<signed char>&    assigns;     // var->val. Pointer to external assignment table.
  const std::vector<double>&  activity;    // var->act. Pointer to external activity table.
  Heap<VarOrder_lt>   heap;
  double              random_seed; // For the internal random number generator

public:
  VarOrder(const std::vector<signed char>& ass, const std::vector<double>& act) :
    assigns(ass), activity(act), heap(VarOrder_lt(act)), random_seed(91648253)
  { }

    inline void newVar(void);
    inline void newVar(int varIndex);
    inline void update(Var x);                  // Called when variable increased in activity.
    inline void undo(Var x);                    // Called when variable is unassigned and may be selected again.
    inline Var  select(double random_freq =.0); // Selects a new, unassigned variable (or 'var_Undef' if none exists).
};


void VarOrder::newVar(void)
{
    heap.setBounds(assigns.size());
    heap.insert(assigns.size()-1);
}

void VarOrder::newVar(int varIndex)
{
    heap.setBounds(assigns.size());
    heap.insert(varIndex);
}

void VarOrder::update(Var x)
{
    if (heap.inHeap(x))
        heap.increase(x);
}

void VarOrder::undo(Var x)
{
    if (!heap.inHeap(x))
        heap.insert(x);
}


Var VarOrder::select(double random_var_freq)
{
  // Random decision:
  /*
    if (drand(random_seed) < random_var_freq && !heap.empty()){
    Var next = irand(random_seed,assigns.size());
    
    // find var which is not undefined or in the heap
    while (toLbool(assigns[next]) == l_Undef && !heap.inHeap(next)) {
    next = irand(random_seed,assigns.size());
    }
    if (toLbool(assigns[next]) == l_Undef) {
    return next;
    }

    // cvc does not necessarily use all variable ids without gaps,
    // so need to check if the picked id is a valid variable.
    //if (toLbool(assigns[next]) == l_Undef && heap.inHeap(next)) {
    //    return next;
    //}
    }
  */
  
  // Activity based decision:
  while (!heap.empty()){
    Var next = heap.getMin();
    if (toLbool(assigns[next]) == l_Undef)
      return next;
  }
  
  return var_Undef;
}

}

//=================================================================================================
#endif