bigrambuffer.java

来自「It is the Speech recognition software. 」· Java 代码 · 共 82 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 bigrams read from disk.
 */
class BigramBuffer extends NGramBuffer {
    
    /**
     * Constructs a BigramBuffer object with the given byte[].
     *
     * @param bigramsOnDisk the byte[] with bigrams
     * @param numberNGrams the number of bigram follows in the byte[]
     */
    public BigramBuffer(byte[] bigramsOnDisk,
			int numberNGrams, boolean bigEndian) {
        super(bigramsOnDisk, numberNGrams, bigEndian);
    }


    /**
     * Finds the bigram probabilities for the given second word in a bigram.
     *
     * @param secondWordID the ID of the second word
     *
     * @return the BigramProbability of the given second word
     */
    public BigramProbability findBigram(int secondWordID) {

        int mid, start = 0, end = getNumberNGrams()-1;
        BigramProbability bigram = null;

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


    /**
     * Returns the BigramProbability of the nth follower.
     *
     * @param nthFollower which follower
     *
     * @return the BigramProbability of the nth follower
     */
    public final BigramProbability getBigramProbability(int nthFollower) {
        int nthPosition = nthFollower * LargeTrigramModel.BYTES_PER_BIGRAM;
	setPosition(nthPosition);

        int wordID = readTwoBytesAsInt();
        int probID = readTwoBytesAsInt();
        int backoffID = readTwoBytesAsInt();
        int firstTrigram = readTwoBytesAsInt();

        return (new BigramProbability
                (nthFollower, wordID, probID, backoffID, firstTrigram));
    }
}