vsids.cpp

多核环境下运行了可满足性分析的工具软件

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// Definition of the (modified) VSIDS decision heuristic.
class VSIDS
{

private: 

  vec<int>      varOrder;      // Ordered list of all variables to select the free one with the highest activity.
  vec<int>      Buckets;       // Used to perform "bucket sort" to sort varOrder.
  unsigned int* varActivity;   // Activity of each variable.
  int           lastSearchPos; // Last search position within varOrder.
  int           numDecisions;  // Number of overall decisions.
 
public:
  
  // Constructor / Destructor.
  VSIDS(unsigned int* varActivityIn);      
  ~VSIDS(void) { /* Nothing to do. */ };

  // Select a free variable and the truth value it should be set to.
  int decide(int* Assignment);      

  // Sort varOrder using a variant of "bucket sort".
  void sort(bool setup);

  // Reset "lastSearchPtr".
  void resetVSIDSPtr(void) { lastSearchPos = numLiterals; }
};

// Constructor.
VSIDS::VSIDS(unsigned int* varActivityIn)
{
  lastSearchPos = numLiterals;
  varActivity   = varActivityIn;
  numDecisions  = 0;
  varOrder.growTo(numLiterals+1,0);
  Buckets.growTo(numBuckets+1,0);

#ifdef PseudoRandom

  srand(0);

#endif

}

// Select the next free variable and the truth value it should be set to.
int VSIDS::decide(int* Assignment)
{    
  // Variables.
  int Literal;

  // Increment number of decisions.
  numDecisions++;

#ifdef PseudoRandom

  // Select the next decision variable randomly.
  if ((numDecisions & PseudoRandomValue) == 0)
    {
      int RND = (rand() % lastSearchPos) + 1;

      // Check the "varActivity" array.
      while(RND > 0)
	{   
	  // Read current literal.
	  Literal = varOrder[RND];
	  
	  // Literal unassigned?
	  if(Assignment[Literal] == 0)
	    {
	      RND--;
	      
#ifdef FixedZeroPolarity

	      // Set "Literal" always to value "0".
	      Literal = (Literal << 1) + 1;

#else

	      // Check whether +Literal or -Literal has the higher activity.
	      Literal = Literal << 1; if (varActivity[Literal] < varActivity[Literal+1]) { Literal++; }

#endif
	      	      
	      // Return variable and truth value.
	      return Literal;
	    }
    
	  RND--;
	}      
    }
  
#endif

  // Check the entire "varActivity" array.
  while(lastSearchPos > 0)
    {   
      // Read current literal.
      Literal = varOrder[lastSearchPos];
      
      // Literal unassigned?
      if(Assignment[Literal] == 0)
        {
	  // Update lastSearchPos for the next decision.
	  lastSearchPos--;

#ifdef FixedZeroPolarity

	  // Set "Literal" always to value "0".
	  Literal = (Literal << 1) + 1;
	  
#else

	  // Check whether +Literal or -Literal has the higher activity.
	  Literal = Literal << 1; if (varActivity[Literal] < varActivity[Literal+1]) { Literal++; }

#endif

	  // Return variable and truth value.
	  return Literal;
        }

      // Decrement lastSearchPos.
      lastSearchPos--;
    }
  
  // No unassigned variable left --> benchmark is satisfiable.
  return 0;
}

// Sort varOrder using a variant of "bucket sort". After performing "sort" 
// the variables are ordered by an increasing activity.
void VSIDS::sort(bool setup)
{ 
  // Variables.
  int i, pos, shifting;
  unsigned int score;

  // Permit normalizing the variable's activities used below during the initialization phase.
  if (setup) { shifting = 0; } else { shifting = shiftAmount; }
  
  // Initialization.
  for(i=0; i<=numBuckets; i++) { Buckets[i] = 0; }
  
  // Compute the variable's score and update "Buckets".
  for(i=1; i<=numLiterals; i++) 
    {
      score = (varActivity[i << 1] + varActivity[(i << 1) + 1]) >> shifting;
      if (score > numBuckets) { Buckets[numBuckets]++; } else { Buckets[score]++; }
    }
  
  // Calculate the final values for all buckets.
  for(i=1; i<=numBuckets; i++) { Buckets[i] += Buckets[i-1]; }
  
  // Now, order the variables by an increasing activity.
  for(i=1; i<=numLiterals; i++)
    {
      score = (varActivity[i << 1] + varActivity[(i << 1) + 1]) >> shifting;
      if (score > numBuckets) { score = numBuckets; } 
      pos = Buckets[score];
      Buckets[score]--;
      varOrder[pos] = i;
    }

  // Reset lastSearchPos.
  resetVSIDSPtr();
}