trigrambuffer.java

来自「It is the Speech recognition software. 」· Java 代码 · 共 78 行

/*
 * 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.language.ngram.large;



/**
 * Implements a buffer for trigrams read from disk.
 */
class TrigramBuffer extends NGramBuffer {
    
    /**
     * Constructs a TrigramBuffer object with the given byte[].
     *
     * @param trigramsOnDisk the byte[] with trigrams
     * @param numberNGrams the number of trigram follows in the byte[]
     */
    public TrigramBuffer(byte[] trigramsOnDisk,
			 int numberNGrams, boolean bigEndian) {
        super(trigramsOnDisk, numberNGrams, bigEndian);
    }


    /**
     * Finds the trigram probability ID for the given third word in a trigram.
     *
     * @param thirdWordID the ID of the third word
     *
     * @return the Trigram Probability ID of the given third word
     */
    public int findProbabilityID(int thirdWordID) {

        // System.out.println("Looking for: " + thirdWordID);

        int mid, start = 0, end = getNumberNGrams();
        // TrigramProbability trigram = null;
        int trigram = -1;

        while ((end - start) > 0) {
            mid = (start + end)/2;
            int midWordID = getWordID(mid);
	    if (midWordID < thirdWordID) {
                start = mid + 1;
            } else if (midWordID > thirdWordID) {
                end = mid;
            } else {
		trigram = getProbabilityID(mid);
                break;
	    }
        }
        return trigram;
    }


    /**
     * Returns the TrigramProbability of the nth follower.
     *
     * @param nthFollower which follower
     *
     * @return the TrigramProbability of the nth follower
     */
    public final int getProbabilityID(int nthFollower) {
        int nthPosition = nthFollower * LargeTrigramModel.BYTES_PER_TRIGRAM;
        setPosition(nthPosition + 2); // the 2 is to skip the word ID
        return readTwoBytesAsInt();
    }
}