solver.c

多核环境下运行了可满足性分析的工具软件

/****************************************************************************************[Solver.C]
MiniSat -- Copyright (c) 2003-2006, Niklas Een, Niklas Sorensson

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, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT
OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
**************************************************************************************************/

#include "Solver.h"
#include "Sort.h"
#include <cmath>

namespace minisat {

  //=================================================================================================
  // Constructor/Destructor:

  Solver::Solver() :
    
    // More parameters:
    //
 
    verbosity        (0)
    
    
    , ok               (true)
    , qhead            (0)
    , simpDB_assigns   (-1)
    , simpDB_props     (0)
    , order_heap       (VarOrderLt(activity))
    , random_seed      (91648253)
    , remove_satisfied (true)
  {}
  
  
  Solver::~Solver()
  {
    for (int i = 0; i < learnts.size(); i++) free(learnts[i]);
    for (int i = 0; i < clauses.size(); i++) free(clauses[i]);
  }
  
  
  //=================================================================================================
  // Minor methods:
  
  
  // Creates a new SAT variable in the solver. If 'decision_var' is cleared, variable will not be
  // used as a decision variable (NOTE! This has effects on the meaning of a SATISFIABLE result).
  //
  Var Solver::newVar(bool sign, bool dvar)
  {
    int v = nVars();
    watches   .push();          // (list for positive literal)
    watches   .push();          // (list for negative literal)
    reason    .push(NULL);
    assigns   .push(toInt(l_Undef));
    level     .push(-1);
    activity  .push(0);
    seen      .push(0);

    polarity    .push((char)sign);
    decision_var.push((char)dvar);

    insertVarOrder(v);
    return v;
  }


  bool Solver::addClause(vec<Lit>& ps)
  {
    assert(decisionLevel() == 0);

    if (!ok)
      return false;
    else{
      // Check if clause is satisfied and remove false/duplicate literals:
      sort(ps);
      Lit p; int i, j;
      for (i = j = 0, p = lit_Undef; i < ps.size(); i++)
	if (value(ps[i]) == l_True || ps[i] == ~p)
	  return true;
	else if (value(ps[i]) != l_False && ps[i] != p)
	  ps[j++] = p = ps[i];
      ps.shrink(i - j);
    }
    
    if (ps.size() == 0)
      return ok = false;
    else if (ps.size() == 1){
      assert(value(ps[0]) == l_Undef);
      uncheckedEnqueue(ps[0]);
      return propagate() == NULL;
    }else{
      Clause* c = Clause_new(ps, false);
      clauses.push(c);
      attachClause(*c);
    }
    
    return true;
  }


  void Solver::attachClause(Clause& c) {
    assert(c.size() > 1);
    watches[toInt(~c[0])].push(&c);
    watches[toInt(~c[1])].push(&c);
    if (c.learnt()) learnts_literals += c.size();
    else            clauses_literals += c.size(); }
  

  void Solver::detachClause(Clause& c) {
    assert(c.size() > 1);
    assert(find(watches[toInt(~c[0])], &c));
    assert(find(watches[toInt(~c[1])], &c));
    remove(watches[toInt(~c[0])], &c);
    remove(watches[toInt(~c[1])], &c);
    if (c.learnt()) learnts_literals -= c.size();
    else            clauses_literals -= c.size(); }


  void Solver::removeClause(Clause& c) {
    detachClause(c);
    free(&c); }


  bool Solver::satisfied(const Clause& c) const {
    for (int i = 0; i < c.size(); i++)
      if (value(c[i]) == l_True)
	return true;
    return false; }
  

  // Revert to the state at given level (keeping all assignment at 'level' but not beyond).
  //
  void Solver::cancelUntil(int level) {
    if (decisionLevel() > level){
      for (int c = trail.size()-1; c >= trail_lim[level]; c--){
	Var     x  = var(trail[c]);
	assigns[x] = toInt(l_Undef);
	insertVarOrder(x); }
      qhead = trail_lim[level];
      trail.shrink(trail.size() - trail_lim[level]);
      trail_lim.shrink(trail_lim.size() - level);
    } }
  
  void Solver::uncheckedEnqueue(Lit p, Clause* from)
  {
    assert(value(p) == l_Undef);
    assigns [var(p)] = toInt(lbool(!sign(p)));  // <<== abstract but not uttermost effecient
    level   [var(p)] = decisionLevel();
    reason  [var(p)] = from;
    trail.push(p);
  }

  /*_________________________________________________________________________________________________
    |
    |  propagate : [void]  ->  [Clause*]
    |  
    |  Description:
    |    Propagates all enqueued facts. If a conflict arises, the conflicting clause is returned,
    |    otherwise NULL.
    |  
    |    Post-conditions:
    |      * the propagation queue is empty, even if there was a conflict.
    |________________________________________________________________________________________________@*/
  Clause* Solver::propagate()
  {
    Clause* confl     = NULL;
    int     num_props = 0;
    
    while (qhead < trail.size()){
      Lit            p   = trail[qhead++];     // 'p' is enqueued fact to propagate.
      vec<Clause*>&  ws  = watches[toInt(p)];
      Clause         **i, **j, **end;
      num_props++;
      
      for (i = j = (Clause**)ws, end = i + ws.size();  i != end;){
	Clause& c = **i++;
	
	// Make sure the false literal is data[1]:
	Lit false_lit = ~p;
	if (c[0] == false_lit)
	  c[0] = c[1], c[1] = false_lit;
	
	assert(c[1] == false_lit);
	
	// If 0th watch is true, then clause is already satisfied.
	Lit first = c[0];
	if (value(first) == l_True){
	  *j++ = &c;
	}else{
	  // Look for new watch:
	  for (int k = 2; k < c.size(); k++)
	    if (value(c[k]) != l_False){
	      c[1] = c[k]; c[k] = false_lit;
	      watches[toInt(~c[1])].push(&c);
	      goto FoundWatch; }
	  
	  // Did not find watch -- clause is unit under assignment:
	  *j++ = &c;
	  if (value(first) == l_False){
	    confl = &c;
	    qhead = trail.size();
	    // Copy the remaining watches:
	    while (i < end)
	      *j++ = *i++;
	  }else
	    uncheckedEnqueue(first, &c);
	}
      FoundWatch:;
      }
      ws.shrink(i - j);
    }
    propagations += num_props;
    simpDB_props -= num_props;
    
    return confl;
  }


  void Solver::removeSatisfied(vec<Clause*>& cs)
  {
    int i,j;
    for (i = j = 0; i < cs.size(); i++){
      if (satisfied(*cs[i]))
	removeClause(*cs[i]);
      else
	cs[j++] = cs[i];
    }
    cs.shrink(i - j);
  }


  /*_________________________________________________________________________________________________
    |
    |  simplify : [void]  ->  [bool]
    |  
    |  Description:
    |    Simplify the clause database according to the current top-level assigment. Currently, the only
    |    thing done here is the removal of satisfied clauses, but more things can be put here.
    |________________________________________________________________________________________________@*/
  bool Solver::simplify()
  {
    assert(decisionLevel() == 0);
    
    if (!ok || propagate() != NULL)
      return ok = false;
    
    if (nAssigns() == simpDB_assigns || (simpDB_props > 0))
      return true;

    // Remove satisfied clauses:
    removeSatisfied(learnts);
    if (remove_satisfied)        // Can be turned off.
      removeSatisfied(clauses);
    
    // Remove fixed variables from the variable heap:
    order_heap.filter(VarFilter(*this));
    
    simpDB_assigns = nAssigns();
    simpDB_props   = clauses_literals + learnts_literals;   // (shouldn't depend on stats really, but it will do for now)

    return true;
  }

} // end namespace minisat