/// <summary>
/// Advances to the next available final state.
/// </summary>
private ByteBuffer Advance()
{
if (position == 0)
{
return(null);
}
while (position > 0)
{
int lastIndex = position - 1;
int arc = arcs[lastIndex];
if (arc == 0)
{
// Remove the current node from the queue.
position--;
continue;
}
// Go to the next arc, but leave it on the stack
// so that we keep the recursion depth level accurate.
arcs[lastIndex] = fsa.GetNextArc(arc);
// Expand buffer if needed.
int bufferLength = this.buffer.Length;
if (lastIndex >= bufferLength)
{
Array.Resize(ref buffer, bufferLength + ExpectedMaxStates);
this.bufferWrapper = ByteBuffer.Wrap(buffer);
}
buffer[lastIndex] = fsa.GetArcLabel(arc);
if (!fsa.IsArcTerminal(arc))
{
// Recursively descend into the arc's node.
PushNode(fsa.GetEndNode(arc));
}
if (fsa.IsArcFinal(arc))
{
bufferWrapper.Clear();
bufferWrapper.Limit = (lastIndex + 1);
return(bufferWrapper);
}
}
return(null);
}
/// <summary>
/// Calculate perfect hash for a given input sequence of bytes. The perfect hash requires
/// that <see cref="FSA"/> is built with <see cref="FSAFlags.Numbers"/> and corresponds to the sequential
/// order of input sequences used at automaton construction time.
/// </summary>
/// <param name="sequence">The byte sequence to calculate perfect hash for.</param>
/// <param name="start">Start index in the sequence array.</param>
/// <param name="length">Length of the byte sequence, must be at least 1.</param>
/// <param name="node">The node to start traversal from, typically the root node (<see cref="FSA.GetRootNode()"/>).</param>
/// <returns>
/// Returns a unique integer assigned to the input sequence in the automaton (reflecting
/// the number of that sequence in the input used to build the automaton). Returns a negative
/// integer if the input sequence was not part of the input from which the automaton was created.
/// The type of mismatch is a constant defined in <see cref="MatchResult"/>.
/// </returns>
/// <seealso cref="PerfectHash(byte[])"/>
public int PerfectHash(byte[] sequence, int start, int length, int node)
{
Debug.Assert((fsa.Flags & FSAFlags.Numbers) != 0, $"FSA not built with {FSAFlags.Numbers} option.");
Debug.Assert(length > 0, "Must be a non-empty sequence.");
int hash = 0;
int end = start + length - 1;
int seqIndex = start;
byte label = sequence[seqIndex];
// Seek through the current node's labels, looking for 'label', update hash.
for (int arc = fsa.GetFirstArc(node); arc != 0;)
{
if (fsa.GetArcLabel(arc) == label)
{
if (fsa.IsArcFinal(arc))
{
if (seqIndex == end)
{
return(hash);
}
hash++;
}
if (fsa.IsArcTerminal(arc))
{
/* The automaton contains a prefix of the input sequence. */
return(MatchResult.AutomatonHasPrefix);
}
// The sequence is a prefix of one of the sequences stored in the automaton.
if (seqIndex == end)
{
return(MatchResult.SequenceIsAPrefix);
}
// Make a transition along the arc, go the target node's first arc.
arc = fsa.GetFirstArc(fsa.GetEndNode(arc));
label = sequence[++seqIndex];
continue;
}
else
{
if (fsa.IsArcFinal(arc))
{
hash++;
}
if (!fsa.IsArcTerminal(arc))
{
hash += fsa.GetRightLanguageCount(fsa.GetEndNode(arc));
}
}
arc = fsa.GetNextArc(arc);
}
if (seqIndex > start)
{
return(MatchResult.AutomatonHasPrefix);
}
else
{
// Labels of this node ended without a match on the sequence.
// Perfect hash does not exist.
return(MatchResult.NoMatch);
}
}