private void UndoOne()
{
Lit l = Lit.LitFromVal(this.trail.Peek());
int x = l.Var;
this.assigns[x] = Assign.UNDEF;
this.reason[x] = null;
this.level[x] = -1;
this.trail.Pop();
}
public bool Search()
{
while (true)
{
Clause confl = this.Propogate();
if (confl != null)
{
//this.PrintLearnts();
if (this.DecisionLevel == 0)
{
return(false);
}
int backtrack_level = 0;
List <Lit> learnt_clause;
this.Analyze(confl, out learnt_clause, out backtrack_level);
//System.Console.WriteLine();
if (backtrack_level == 0)
{
int y = 0;
}
this.CancelUntil(Math.Max(backtrack_level, 0)); // 0 for root level?
this.Record(learnt_clause);
}
else
{
if (this.NAssigns == this.NVars)
{
return(true);
}
else // Pick new variable
{
foreach (var x in this.assigns)
{
if (x.Value == Assign.UNDEF)
{
this.Assume(Lit.LitFromVal((x.Key * 2) + 1));
break;
}
}
}
}
}
return(true);
}
// Page 15
private void Analyze(Clause confl, out List <Lit> out_learnt, out int btlevel)
{
int counter = 0;
Lit p = Lit.LIT_UNDEF;
List <Lit> p_reason;
List <int> seen = new List <int>(); // May need to optimize this
btlevel = 0;
out_learnt = new List <Lit>();
out_learnt.Add(Lit.LIT_UNDEF); // Reserve space for lits[0]
do
{
p_reason = confl.CalcReason(this, p);
foreach (Lit q in p_reason)
{
if (!seen.Contains(q.Var))
{
seen.Add(q.Var);
if (this.level[q.Var] == this.DecisionLevel)
{
++counter;
}
else if (this.level[q.Var] > 0)
{
//out_learnt.Add(Lit.LitFromVal(q.Val));
out_learnt.Add(Lit.NegativeLit(q));
btlevel = Math.Max(btlevel, this.level[q.Var]);
}
}
}
do
{
p = Lit.LitFromVal(this.trail.Peek());
confl = this.reason[p.Var];
this.UndoOne();
} while (!seen.Contains(p.Var));
--counter;
} while(counter > 0);
out_learnt[0] = Lit.NegativeLit(p);
}