SentenceHMMStateArc.java

/*
 * Copyright 1999-2002 Carnegie Mellon University.  
 * Portions Copyright 2002 Sun Microsystems, Inc.  
 * Portions Copyright 2002 Mitsubishi Electric Research Laboratories.
 * All Rights Reserved.  Use is subject to license terms.
 * 
 * See the file "license.terms" for information on usage and
 * redistribution of this file, and for a DISCLAIMER OF ALL 
 * WARRANTIES.
 *
 */

package edu.cmu.sphinx.linguist.flat;

import edu.cmu.sphinx.linguist.SearchState;
import edu.cmu.sphinx.linguist.SearchStateArc;

/**
 * Represents a transition in a sentence HMM. Each transition is described by the next state and the associated acoustic
 * and language probability for the transition.
 * <p>
 * All probabilities are in the LogMath log domain
 */
public class SentenceHMMStateArc implements SearchStateArc {

    private final SentenceHMMState nextState;
    private final float logLanguageProbability;
    private final float logInsertionProbability;
    private final int hashCode;


    /**
     * Creates a SentenceHMMStateArc
     *
     * @param nextState               the next state
     * @param logLanguageProbability  the log language probability
     * @param logInsertionProbability the log insertion probability
     */
    public SentenceHMMStateArc(SentenceHMMState nextState,
                               float logLanguageProbability,
                               float logInsertionProbability) {
        this.nextState = nextState;
        this.logLanguageProbability = logLanguageProbability;
        this.logInsertionProbability = logInsertionProbability;

        hashCode = 111 + nextState.hashCode() +
                17 * Float.floatToIntBits(logLanguageProbability) +
                23 * Float.floatToIntBits(logInsertionProbability);

    }


    /**
     * Determines if the given object is equal to this object
     *
     * @param o the object to compare to
     * @return <code>true</code> if the objects are equal
     */
    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        } else if (o instanceof SentenceHMMStateArc) {
            SentenceHMMStateArc other = (SentenceHMMStateArc) o;
            return nextState == other.nextState &&
                    logLanguageProbability == other.logLanguageProbability &&
                    logInsertionProbability == other.logInsertionProbability;

        } else {
            return false;
        }
    }


    /**
     * Returns a hashCode for this object
     *
     * @return the hashCode
     */
    @Override
    public int hashCode() {
        return hashCode;
    }


    /**
     * Retrieves the next state
     *
     * @return the next state
     */
    public SearchState getState() {
        return nextState;
    }


    /**
     * For backwards compatibility
     * <p>
     * Returns the next state as a SentenceHMSMtate
     *
     * @return the next state
     */
    public SentenceHMMState getNextState() {
        return (SentenceHMMState) getState();
    }


    /**
     * Retrieves the language transition probability for this transition
     *
     * @return the language  transition probability in the logmath log domain
     */
    public float getLanguageProbability() {
        return logLanguageProbability;
    }


    /**
     * Retrieves the insertion probability for this transition
     *
     * @return the insertion probability  in the logmath log domain
     */
    public float getInsertionProbability() {
        return logInsertionProbability;
    }


    /**
     * Gets the composite probability of entering this state
     *
     * @return the log probability
     */
    public float getProbability() {
        return logLanguageProbability +
                logInsertionProbability;
    }
}