/// <summary>
/// And function for FDD's.
/// </summary>
/// <param name="u1">left side of the expression</param>
/// <param name="u2">right side of the expression</param>
/// <returns>a new BDD where u1 and u2 are bitwise and'ed</returns>
public static Bdd And(Fdd u1, Fdd u2)
{
int u1Size = Size(u1);
int u2Size = Size(u2);
int MinSize = Min(u1Size, u2Size);
Bdd result = new Bdd(false);
for (int i = 0; i < MinSize; i++)
{
result = Kernel.Or(result, Kernel.And(new Bdd(u1.Var + i), new Bdd(u2.Var + i)));
}
if (u1Size != u2Size)
{
if (u1Size > u2Size) //you reach this state when 2 Fdds does not have the same number
{ //of bits. What happens is then the smallest get buffered with 0's
for (int i = MinSize; i < u1Size; i++)
{
result = Kernel.Or(result, Kernel.And(new Bdd(u1.Var + i), new Bdd(false)));
}
}
else
{
for (int i = MinSize; i < u2Size; i++)
{
result = Kernel.Or(result, Kernel.And(new Bdd(false), new Bdd(u2.Var + i)));
}
}
}
return(result);
}
/// <summary>
/// restricts an FDD out of an expression, by giving it an integer value.
/// </summary>
/// <param name="root">the root of the tree the Fdd is a part of</param>
/// <param name="fdd">the Fdd to restrict</param>
/// <param name="restrictValue">the given ristrict value, must be between 0 and maxvalue of the Fdd.</param>
/// <returns>the restricted Bdd</returns>
public static Bdd Restrict(Bdd root, Fdd fdd, int restrictValue)
{
bool[] B = ToBitPattern(restrictValue);
for (int i = 0; i < B.Length; i++)
{
root = Kernel.Restrict(root, fdd.Var + i, B[i]);
}
RestrictDictionary.Add(fdd.Var, restrictValue);
return(root);
}
/// <summary>
/// Enforces maxvalues by disallowing values normally room for with the size of bits in an fdd
/// Value is normally expected to be the same as used in the constructor of the fdd.
/// Note: (powers of 2) -1) does not need to be constrained: 7, 255 etc.
/// </summary>
/// <param name="fdd">The fdd to constrain</param>
/// <param name="value">The values to enforce</param>
public static Bdd EnforceMaxValue(Fdd fdd, int value)
{
Bdd result;
//Always allow all bits where most significant bit isn't set
result = Kernel.Not(new Bdd(fdd.Var));
int start = (int)Math.Pow(2, Size(fdd) - 1); //lowest number with most significant bit set
for (int i = start; i <= value; i++)
{
result = Kernel.Or(result, Equal(fdd, i));
}
return(result);
}
/// <summary>
/// Creates a hard binding sort of like an fdd restrict.
/// Difference is that the binding will persist no matter
/// what changes is later added.
/// </summary>
/// <param name="fdd">the Fdd to create a binding on</param>
/// <param name="value">the constant number that is assigned to the Fdd.</param>
/// <returns></returns>
public static Bdd Equal(Fdd fdd, int value)
{
if (Log2(value) > FddDictionary[fdd.Var]) //value larger than fdd can hold.
{
return(new Bdd(false));
}
bool[] b = ToBitPattern(value, Size(fdd));
Bdd result = new Bdd(true);
for (int i = 0; i < b.Length; i++)
{
if (b[i])
{
result = Kernel.And(result, new Bdd(fdd.Var + i));
}
else
{
result = Kernel.And(result, Kernel.Not(new Bdd(fdd.Var + i)));
}
}
return(result);
}
/// <summary>
/// returns the bit-size of a given FDD.
/// </summary>
/// <param name="fdd">The FDD to get the size of</param>
/// <returns></returns>
public static int Size(Fdd fdd)
{
return(FddDictionary[fdd.Var]);
}
/// <summary>
/// Compares Fdd's based on their position in the FDD array
/// </summary>
/// <param name="fdd">The FDD to compare the current FDD to</param>
/// <returns>true if the FDD's have the same index, else false</returns>
public bool Equals(Fdd fdd)
{
return(this.GetHashCode() == fdd.GetHashCode()); //GetHashCode is unique
}
