/// <summary>
/// Evaluates the reachable state space of a transition system given a initial state.
/// </summary>
/// <param name="I">The Bdd representing the initial state of the system.</param>
/// <param name="T">The Bdd representing all possible transition in the system.</param>
/// <param name="bpl">A list of variable pairs that represent pre- and post-states.</param>
/// <returns>The Bdd representing the reachable state space.</returns>
public static Bdd ReachableStates(Bdd I, Bdd T, BddPairList bpl)
{
Bdd Rp;
Bdd R = new Bdd(false);
do
{
Rp = R;
R = I | ExecuteTransition(R, T, bpl);
}while (!R.Equals(Rp));
return(R);
}
private static bool IsOnTrace(Bdd I, Bdd E, Bdd T, BddPairList bpl, int tracelength)
{
int count = 0;
Bdd R = I;
while (count < tracelength)
{
R = ExecuteTransition(R, T, bpl);
count++;
}
Bdd test = E >= R;
return(test.U == Kernel.bddtrue);
}
/// <summary>
/// Evaluates the number of transitions it takes to reach a state from a given initial
/// state in a transition system.
/// </summary>
/// <param name="I">The Bdd representing the initial state of the system.</param>
/// <param name="E">The state that what to be reached.</param>
/// <param name="T">The Bdd representing all possible transition in the system.</param>
/// <param name="bpl">A list of variable pairs that represent pre- and post-states.</param>
/// <returns>Number of transitions needed. -1 if no trace exists.</returns>
public static int Tracelength(Bdd I, Bdd E, Bdd T, BddPairList bpl)
{
int tracelength = 0;
Bdd Rp, test;
Bdd R = I;
do
{
Rp = R;
R = I | ExecuteTransition(R, T, bpl);
test = E >= R;
if (R.Equals(Rp) & test.U != Kernel.bddtrue)
{
return(-1);
}
tracelength++;
}while (test.U != Kernel.bddtrue);
return(tracelength);
}
private static int VarListQuantification(ref BddPairList varList, int u, Op op)
{
if (quantiHash.ContainsKey(u))
{
return(quantiHash[u]);
}
int low, high;
if (!IsTerminal(Low(u)))
{
low = VarListQuantification(ref varList, Low(u), op);
}
else
{
low = Low(u);
}
if (!IsTerminal(High(u)))
{
high = VarListQuantification(ref varList, High(u), op);
}
else
{
high = High(u);
}
int newU;
if (varList.QuantificationContainsKey(Var(u)))
{
newU = Apply(op, low, high);
}
else
{
newU = Mk(Var(u), low, high);
}
quantiHash.Add(u, newU);
return(newU);
}
private static int AppEx(Op op, int u1, int u2, ref BddPairList varList)
{
int u;
if (GAppEx.ContainsKey(u1, u2, op))
{
return(GAppEx[u1, u2, op]);
}
if (IsTerminal(u1) && IsTerminal(u2))
{
return(Lookup[(int)(byte)op, u1 * 2 + u2]);
}
else
{
switch (Var(u1).CompareTo(Var(u2)))
{
case 0: //equals
u = Mk(Var(u1), AppEx(op, Low(u1), Low(u2), ref varList), AppEx(op, High(u1), High(u2), ref varList));
break;
case -1: //less than
u = Mk(Var(u1), AppEx(op, Low(u1), u2, ref varList), AppEx(op, High(u1), u2, ref varList));
break;
default: //greater than
u = Mk(Var(u2), AppEx(op, u1, Low(u2), ref varList), AppEx(op, u1, High(u2), ref varList));
break;
}
}
if (varList.QuantificationContainsKey(Var(u)))
{
u = Apply(Op.DIS, Low(u), High(u));
}
GAppEx.Add(u1, u2, op, u);
return(u);
}
private static int VarListCompose(ref BddPairList bpl, int u)
{
if (u == 0 || u == 1)
{
return(u);
}
if (composeHash.ContainsKey(u))
{
return(composeHash[u]);
}
int newU = u;
if (bpl.ComposeContainsKey(Var(u)))
{
newU = Mk(bpl[Var(u)], VarListCompose(ref bpl, Low(u)), VarListCompose(ref bpl, High(u)));
}
else
{
newU = Mk(Var(u), VarListCompose(ref bpl, Low(u)), VarListCompose(ref bpl, High(u)));
}
composeHash.Add(u, newU);
return(newU);
}
//#######################################################################################
/// <summary>
/// Universal quantification on a list of variables.
/// </summary>
/// <param name="varList">List of variables</param>
/// <param name="root">bdd</param>
/// <returns>Resulting Bdd</returns>
public static Bdd VarListForAll(BddPairList varList, Bdd root)
{
int u = VarListQuantification(ref varList, root.U, Op.CON);
return(Bdd.CreateBdd(u));
}
//###########################################################################################
/// <summary>
/// Boolean operation and existential quantification on a list of variables.
/// The same operation as first using Apply() and then VarListExists().
/// </summary>
/// <param name="operatoR">Boolean operator</param>
/// <param name="root1">bdd</param>
/// <param name="root2">bdd</param>
/// <param name="varList">List of variables</param>
/// <returns>Resulting Bdd</returns>
public static Bdd ApplyExists(Op operatoR, Bdd root1, Bdd root2, BddPairList varList)
{
int u = AppEx(operatoR, root1.U, root2.U, ref varList);
return(Bdd.CreateBdd(u));
}
//################################################################################################
/// <summary>
/// Existential quantification on a list of variables.
/// </summary>
/// <param name="varList">List of variables</param>
/// <param name="root">bdd</param>
/// <returns>Resulting Bdd</returns>
public static Bdd VarListExists(BddPairList varList, Bdd root)
{
int u = VarListQuantification(ref varList, root.U, Op.DIS);
return(Bdd.CreateBdd(u));
}
/// <summary>
/// Substitution of a list of variablepairs in a Bdd.
/// </summary>
/// <param name="bpl">Variablepairlist</param>
/// <param name="root">bdd</param>
/// <returns>Resulting Bdd</returns>
public static Bdd VarListCompose(BddPairList bpl, Bdd root)
{
int u = VarListCompose(ref bpl, root.U);
return(Bdd.CreateBdd(u));
}
/// <summary>
/// List a possible sequence of transitions to reach a state from a given initial
/// state in a transition system.
/// </summary>
/// <param name="I">The Bdd representing the initial state of the system.</param>
/// <param name="E">The state that what to be reached.</param>
/// <param name="T">The Bdd representing all possible transition in the system.</param>
/// <param name="transitionlist">A collection of all possible transition in the
/// transition system and a string that describes each transition.</param>
/// <param name="bpl">A list of variable pairs that represent pre- and post-states.</param>
/// <param name="tracelength">The number of transitions it takes to reach a state from a given initial
/// state.</param>
/// <returns>A string representing a possible sequence of transitions. "No trace to state" if no trace exists.</returns>
public static string FindTrace(Bdd I, Bdd E, Bdd T, Dictionary <Bdd, string> transitionlist, BddPairList bpl, int tracelength)
{
Bdd R;
if (tracelength == 0)
{
return("[]");
}
else if (tracelength > 0)
{
foreach (KeyValuePair <Bdd, string> trans in transitionlist)
{
R = ExecuteTransition(I, trans.Key, bpl);
if (IsOnTrace(R, E, T, bpl, tracelength - 1))
{
return(trans.Value + " " + FindTrace(R, E, T, transitionlist, bpl, tracelength - 1));
}
}
}
return("No trace to the state.");
}
private static Bdd ExecuteTransition(Bdd R, Bdd T, BddPairList bpl)
{
Bdd temp = Kernel.ApplyExists(Op.CON, T, R, bpl);
return(Kernel.VarListCompose(bpl, temp));
}
