/// <summary>Create a Boolean classifier.</summary>
/// <param name="solver">Character algebra (the algebra is not stored in the classifier)</param>
/// <param name="bdd">Elements that map to true.</param>
public BooleanClassifier(CharSetSolver solver, BDD bdd)
{
// We want to optimize for ASCII, so query the BDD for each ASCII character in
// order to precompute a lookup table we'll use at match time.
var ascii = new bool[128];
for (int i = 0; i < ascii.Length; i++)
{
ascii[i] = bdd.Contains(i);
}
// At this point, we'll never consult the BDD for ASCII characters, so as an
// optimization we can remove them from the BDD in hopes of simplifying it and making
// it faster to query for the non-ASCII characters we will use it for. However, while
// this is typically an optimization, it isn't always: the act of removing some
// characters from the BDD can actually make the branching more complicated. The
// extreme case of this is when the BDD is True, meaning everything maps to True, which
// is as simple a BDD as you can get. In such a case, even though it's rare, this would
// definitively be a deoptimization, so we avoid doing so. Other trivial cases are handled
// by And itself, e.g. if the BDD == False, then And will just return False.
if (!bdd.IsFull)
{
bdd = solver.And(solver._nonAscii, bdd);
}
_ascii = ascii;
_nonAscii = bdd;
}
public bool IsTrue(char c)
{
bool[] ascii = _ascii;
return(c < ascii.Length ? ascii[c] : _nonAscii.Contains(c));
}