thread_decide.cpp

多核环境下运行了可满足性分析的工具软件

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MiraXT -- Copyright (c) 2007, Tobias Schubert, Matthew Lewis, Natalia Kalinnik, Bernd Becker 

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// Selects and assigns the next variable. Not only "free" variables, but also all current 
// implications for which "Boolean Constraint Propagation" hasn't been done so far, will 
// be covered and selected first.
inline int Thread::decide(void)
{
  // Any unprocessed implications left?
  if (sEI != ucEI) { return decideImplication(); }
  
  // Increment the number of calls of "decide".
  decisionCount++;

  // What about deleting some clauses?
  if (currentDL == 0 && (DSprogress+256) < ucEI) { cleanClauseDB(); DSprogress = ucEI; }
  
  // Let's check if it is time for cleaning the database, dividing the current subproblem,
  // reducing the literal's activities, performing a restart, or terminating the search process.
  if ((decisionCount & 127) == 0)
    {  
      // Is it time to delete some clauses with a low activity?
      if(numClausesAdded > cleanOften && currentDL != 0)
        {
	  cleanOften = cleanOften + (cleanOften >> 2);
	  if (cleanOften > 16384) { cleanOften = 16384; }
	  numClausesAdded = 0;
	  cleanClauseDB();
        }
      
      // Is there some other thread waiting for a new and unchecked subproblem?
      if (currentDL != 0 && theDecisionQueue->needMoreDecisionStacks() == true)
        { theDecisionQueue->addDecisionStack(currentDL, DLLookupArray, DecisionStack); }
      
      // Is it time to reduce the literal's activities?
      if (literalActivityIncCount > reduceOften) 
        {
	  literalActivityIncCount = 0; 
	  reduceLiteralActivity();
	  myVSIDS->sort(false);
        }
      
      // What about a restart?
      if (restartCount > restartInc)
        {
	  restartCount = 0;
   	  restartInc = restartInc + (restartInc >> 1);
	  if (restartInc > restartMax) { restartInc = 500; restartMax += restartMax; }
	  myVSIDS->sort(false);
	  restartSearch();
        }

      // Check if we reached the given CPU limit?
      if ((decisionCount & 1023) == 0)
        { if ((getTime() - masterControl->startTime) >= maxTime) { return 0; } }

      // Terminate the search?
      if (masterControl->masterDone != 0) { return 0; }
    }

  //  Now it's time to select and assign the next variable.
  int myDecision = myVSIDS->decide(Assignment);
  if (myDecision != 0) { pushDecision(myDecision); }
  return myDecision;
}

// Reset "unitClauseSearchArray" (Implication Queue Sorting).
inline void Thread::resetUnitClauseSearchArray()
{ for(int L=0; L<=IQSize; L++) { unitClauseSearchArray[L].clearFast(); } }

// Swap the implications on positions "P1" and "P2" within the decision stack.
inline void Thread::swapImplicationsDS(int P1, int P2)
{    
  int H             = DecisionStack[P1];
  DecisionStack[P1] = DecisionStack[P2];
  DecisionStack[P2] = H;
  
  DSLookupArray[H >> 1]                 = P2;
  DSLookupArray[DecisionStack[P1] >> 1] = P1;
  
  H                   = forcingClauseDS[P1];
  forcingClauseDS[P1] = forcingClauseDS[P2];
  forcingClauseDS[P2] = H;
}

// Determine the correct implication queue of the implication "Literal" within "unitClauseSearchArray".
inline void Thread::addUnitDecisionSort(int Literal) 
{
  // Take a look at the "normalized" activity of "-Literal".
  unsigned int T = (literalActivity[Literal ^ 1] >> 16);

  // What about the activity?
  if (T != 0)
    {
      // Ok, so let's decide in which implication queue of "unitClauseSearchArray"
      // the current literal should be stored (implications for which "T" is equal 
      // zero will be processed in a chronological manner after processing all 
      // implications within the different implication queues first). 
      T = IQSize + ((T - IQSize) & -(T < IQSize));
      unitClauseSearchArray[T].push(Literal);
    }
}

// Determine the next implication to be processed.
inline bool Thread::decideImplication(void)
{
  // Get the first non-empty implication queue of "unitClauseSearchArray", 
  // starting with the queue storing the "most active implications" (i.e., 
  // storing the implications for which the literal with the opposite truth 
  // is currently very "active").
  int myPos = IQSize; while(myPos > 0 && unitClauseSearchArray[myPos].size() == 0) { myPos--; }
   
  // Is there any non-empty implication within the queue of "unitClauseSearchArray"?
  // If not, all remaining implications will be treated in chronological order.
  if(myPos > 0)
    {
      // What's the ID of the non-empty queue?
      if (myPos < IQSize)
        {
	  swapImplicationsDS(sEI,DSLookupArray[unitClauseSearchArray[myPos].last() >> 1]);
	  unitClauseSearchArray[myPos].pop();
        }
      else
        {
	  // Currently, the implication queue with ID "IQSize" is not empty,
	  // meaning that we have some implications with really a high activity. 
	  // So, let's check in detail which implication should be processed first.

	  unsigned int  MaxVal   = 0;
	  int           MaxPos   = 0;
	  int*          UCSA     = unitClauseSearchArray[IQSize];
	  int           sizeUCSA = unitClauseSearchArray[IQSize].size();
	                myPos    = 0;
	  int           myLit;
	  
	  while(myPos < sizeUCSA)
            {
	      myLit = UCSA[myPos];

	      if (literalActivity[myLit ^ 1] > MaxVal) 
                { MaxVal = literalActivity[myLit ^ 1]; MaxPos = myPos; }

	      myPos++;
            }
	  
	  MaxVal = UCSA[MaxPos];
	  unitClauseSearchArray[IQSize].rem(MaxPos);
	  swapImplicationsDS(sEI,DSLookupArray[MaxVal >> 1]);
        }
    }

  // Let's increment the "Stack End Index", since the next implication gets processed soon.
  sEI++;

  // Everything went fine.
  return true;
}