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Morfologik Finite State Automata Traversal.
package morfologik.fsa;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.util.BitSet;
import java.util.Collections;
import java.util.Iterator;
import java.util.Locale;
import java.util.Set;
/**
* This is a top abstract class for handling finite state automata. These
* automata are arc-based, a design described in Jan Daciuk's Incremental
* Construction of Finite-State Automata and Transducers, and Their Use in the
* Natural Language Processing (PhD thesis, Technical University of Gdansk).
*/
public abstract class FSA implements Iterable {
/**
* @return Returns the identifier of the root node of this automaton. Returns
* 0 if the start node is also the end node (the automaton is empty).
*/
public abstract int getRootNode();
/**
* @param node
* Identifier of the node.
* @return Returns the identifier of the first arc leaving node
* or 0 if the node has no outgoing arcs.
*/
public abstract int getFirstArc(int node);
/**
* @param arc
* The arc's identifier.
* @return Returns the identifier of the next arc after arc and
* leaving node. Zero is returned if no more arcs are
* available for the node.
*/
public abstract int getNextArc(int arc);
/**
* @param node
* Identifier of the node.
* @param label
* The arc's label.
* @return Returns the identifier of an arc leaving node and
* labeled with label. An identifier equal to 0 means the
* node has no outgoing arc labeled label.
*/
public abstract int getArc(int node, byte label);
/**
* @param arc
* The arc's identifier.
* @return Return the label associated with a given arc.
*/
public abstract byte getArcLabel(int arc);
/**
* @param arc
* The arc's identifier.
* @return Returns true if the destination node at the end of
* this arc corresponds to an input sequence created when
* building this automaton.
*/
public abstract boolean isArcFinal(int arc);
/**
* @param arc
* The arc's identifier.
* @return Returns true if this arc does not have a
* terminating node (@link {@link #getEndNode(int)} will throw an
* exception). Implies {@link #isArcFinal(int)}.
*/
public abstract boolean isArcTerminal(int arc);
/**
* @param arc
* The arc's identifier.
* @return Return the end node pointed to by a given arc.
* Terminal arcs (those that point to a terminal state) have no end
* node representation and throw a runtime exception.
*/
public abstract int getEndNode(int arc);
/**
* @return Returns a set of flags for this FSA instance.
*/
public abstract Set getFlags();
/**
* @param node
* Identifier of the node.
* @return Calculates and returns the number of arcs of a given node.
*/
public int getArcCount(int node) {
int count = 0;
for (int arc = getFirstArc(node); arc != 0; arc = getNextArc(arc)) {
count++;
}
return count;
}
/**
* @param node
* Identifier of the node.
*
* @return Returns the number of sequences reachable from the given state if
* the automaton was compiled with {@link FSAFlags#NUMBERS}. The size
* of the right language of the state, in other words.
*
* @throws UnsupportedOperationException
* If the automaton was not compiled with {@link FSAFlags#NUMBERS}.
* The value can then be computed by manual count of
* {@link #getSequences}.
*/
public int getRightLanguageCount(int node) {
throw new UnsupportedOperationException("Automaton not compiled with " + FSAFlags.NUMBERS);
}
/**
* Returns an iterator over all binary sequences starting at the given FSA
* state (node) and ending in final nodes. This corresponds to a set of
* suffixes of a given prefix from all sequences stored in the automaton.
*
*
* The returned iterator is a {@link ByteBuffer} whose contents changes on
* each call to {@link Iterator#next()}. The keep the contents between calls
* to {@link Iterator#next()}, one must copy the buffer to some other
* location.
*
*
*
* Important. It is guaranteed that the returned byte buffer is backed
* by a byte array and that the content of the byte buffer starts at the
* array's index 0.
*
*
* @param node
* Identifier of the starting node from which to return subsequences.
* @return An iterable over all sequences encoded starting at the given node.
*/
public Iterable getSequences(final int node) {
if (node == 0) {
return Collections. emptyList();
}
return new Iterable() {
public Iterator iterator() {
return new ByteSequenceIterator(FSA.this, node);
}
};
}
/**
* An alias of calling {@link #iterator} directly ({@link FSA} is also
* {@link Iterable}).
*
* @return Returns all sequences encoded in the automaton.
*/
public final Iterable getSequences() {
return getSequences(getRootNode());
}
/**
* Returns an iterator over all binary sequences starting from the initial FSA
* state (node) and ending in final nodes. The returned iterator is a
* {@link ByteBuffer} whose contents changes on each call to
* {@link Iterator#next()}. The keep the contents between calls to
* {@link Iterator#next()}, one must copy the buffer to some other location.
*
*
* Important. It is guaranteed that the returned byte buffer is backed
* by a byte array and that the content of the byte buffer starts at the
* array's index 0.
*
*/
public final Iterator iterator() {
return getSequences().iterator();
}
/**
* Visit all states. The order of visiting is undefined. This method may be
* faster than traversing the automaton in post or preorder since it can scan
* states linearly. Returning false from {@link StateVisitor#accept(int)}
* immediately terminates the traversal.
*
* @param v Visitor to receive traversal calls.
* @param A subclass of {@link StateVisitor}.
* @return Returns the argument (for access to anonymous class fields).
*/
public T visitAllStates(T v) {
return visitInPostOrder(v);
}
/**
* Same as {@link #visitInPostOrder(StateVisitor, int)}, starting from root
* automaton node.
*
* @param v Visitor to receive traversal calls.
* @param A subclass of {@link StateVisitor}.
* @return Returns the argument (for access to anonymous class fields).
*/
public T visitInPostOrder(T v) {
return visitInPostOrder(v, getRootNode());
}
/**
* Visits all states reachable from node in postorder. Returning
* false from {@link StateVisitor#accept(int)} immediately terminates the
* traversal.
*
* @param v Visitor to receive traversal calls.
* @param A subclass of {@link StateVisitor}.
* @param node Identifier of the node.
* @return Returns the argument (for access to anonymous class fields).
*/
public T visitInPostOrder(T v, int node) {
visitInPostOrder(v, node, new BitSet());
return v;
}
/** Private recursion. */
private boolean visitInPostOrder(StateVisitor v, int node, BitSet visited) {
if (visited.get(node))
return true;
visited.set(node);
for (int arc = getFirstArc(node); arc != 0; arc = getNextArc(arc)) {
if (!isArcTerminal(arc)) {
if (!visitInPostOrder(v, getEndNode(arc), visited))
return false;
}
}
return v.accept(node);
}
/**
* Same as {@link #visitInPreOrder(StateVisitor, int)}, starting from root
* automaton node.
*
* @param v Visitor to receive traversal calls.
* @param A subclass of {@link StateVisitor}.
* @return Returns the argument (for access to anonymous class fields).
*/
public T visitInPreOrder(T v) {
return visitInPreOrder(v, getRootNode());
}
/**
* Visits all states in preorder. Returning false from
* {@link StateVisitor#accept(int)} skips traversal of all sub-states of a
* given state.
*
* @param v Visitor to receive traversal calls.
* @param A subclass of {@link StateVisitor}.
* @param node Identifier of the node.
* @return Returns the argument (for access to anonymous class fields).
*/
public T visitInPreOrder(T v, int node) {
visitInPreOrder(v, node, new BitSet());
return v;
}
/**
* @param in The input stream.
* @return Reads all remaining bytes from an input stream and returns
* them as a byte array.
* @throws IOException Rethrown if an I/O exception occurs.
*/
protected static final byte[] readRemaining(InputStream in) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buffer = new byte[1024 * 8];
int len;
while ((len = in.read(buffer)) >= 0) {
baos.write(buffer, 0, len);
}
return baos.toByteArray();
}
/** Private recursion. */
private void visitInPreOrder(StateVisitor v, int node, BitSet visited) {
if (visited.get(node)) {
return;
}
visited.set(node);
if (v.accept(node)) {
for (int arc = getFirstArc(node); arc != 0; arc = getNextArc(arc)) {
if (!isArcTerminal(arc)) {
visitInPreOrder(v, getEndNode(arc), visited);
}
}
}
}
/**
* A factory for reading automata in any of the supported versions.
*
* @param stream
* The input stream to read automaton data from. The stream is not
* closed.
* @return Returns an instantiated automaton. Never null.
* @throws IOException
* If the input stream does not represent an automaton or is
* otherwise invalid.
*/
public static FSA read(InputStream stream) throws IOException {
final FSAHeader header = FSAHeader.read(stream);
switch (header.version) {
case FSA5.VERSION:
return new FSA5(stream);
case CFSA.VERSION:
return new CFSA(stream);
case CFSA2.VERSION:
return new CFSA2(stream);
default:
throw new IOException(
String.format(Locale.ROOT, "Unsupported automaton version: 0x%02x", header.version & 0xFF));
}
}
/**
* A factory for reading a specific FSA subclass, including proper casting.
*
* @param stream
* The input stream to read automaton data from. The stream is not
* closed.
* @param clazz A subclass of {@link FSA} to cast the read automaton to.
* @param A subclass of {@link FSA} to cast the read automaton to.
* @return Returns an instantiated automaton. Never null.
* @throws IOException
* If the input stream does not represent an automaton, is otherwise
* invalid or the class of the automaton read from the input stream
* is not assignable to clazz.
*/
public static T read(InputStream stream, Class clazz) throws IOException {
FSA fsa = read(stream);
if (!clazz.isInstance(fsa)) {
throw new IOException(String.format(Locale.ROOT, "Expected FSA type %s, but read an incompatible type %s.",
clazz.getName(), fsa.getClass().getName()));
}
return clazz.cast(fsa);
}
}
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