/// <summary>
/// Returns a new formula that repairs the order after a substitution.
/// </summary>
/// <param name="level">Variable level of the new node.</param>
/// <param name="lo">The node's lo branch.</param>
/// <param name="hi">The node's hi branch.</param>
/// <returns></returns>
private DDIndex RepairOrder(int level, DDIndex lo, DDIndex hi)
{
var loNode = this.Manager.MemoryPool[lo.GetPosition()];
var hiNode = this.Manager.MemoryPool[hi.GetPosition()];
loNode = lo.IsComplemented() ? Flip(loNode) : loNode;
hiNode = hi.IsComplemented() ? Flip(hiNode) : hiNode;
var loConst = lo.IsConstant();
var hiConst = hi.IsConstant();
var loLevel = loConst ? int.MaxValue : loNode.Variable;
var hiLevel = hiConst ? int.MaxValue : hiNode.Variable;
if (level < loLevel && level < hiLevel)
{
return(this.Manager.Allocate(new BDDNode(level, lo, hi)));
}
else if (loLevel < hiLevel)
{
var l = RepairOrder(level, loNode.Low, hi);
var h = RepairOrder(level, loNode.High, hi);
return(this.Manager.Allocate(new BDDNode(loNode.Variable, l, h)));
}
else if (loLevel > hiLevel)
{
var l = RepairOrder(level, lo, hiNode.Low);
var h = RepairOrder(level, lo, hiNode.High);
return(this.Manager.Allocate(new BDDNode(hiNode.Variable, l, h)));
}
else
{
var l = RepairOrder(level, loNode.Low, hiNode.Low);
var h = RepairOrder(level, loNode.High, hiNode.High);
return(this.Manager.Allocate(new BDDNode(loNode.Variable, l, h)));
}
}
/// <summary>
/// Gets the "level" for the node, where the maximum
/// value is used for constants.
/// </summary>
/// <param name="idx">The node index.</param>
/// <param name="node">The node.</param>
/// <returns></returns>
private int Level(DDIndex idx, BDDNode node)
{
return(idx.IsConstant() ? int.MaxValue : node.Variable);
}