tokenqueue.java

SRI international 发布的OAA框架软件

package antlr_oaa;

/* ANTLR Translator Generator
 * Project led by Terence Parr at http://www.jGuru.com
 * Software rights: http://www.antlr.org/RIGHTS.html
 *
 * $Id: TokenQueue.java,v 1.1 2002/11/08 17:37:38 agno Exp $
 */

/** A private circular buffer object used by the token buffer */
class TokenQueue {
	// Physical circular buffer of tokens
	private Token[] buffer;
	// buffer.length-1 for quick modulous
	private int sizeLessOne;
	// physical index of front token
	private int offset;
	// number of tokens in the queue
	protected int nbrEntries;


	public TokenQueue(int minSize) {
		// Find first power of 2 >= to requested size
		int size;
		for (size = 2; size < minSize; size *= 2) {;}
		init(size);
	}
	/** Add token to end of the queue
	 * @param tok The token to add
	 */
	public final void append(Token tok)
	{
		if (nbrEntries == buffer.length)
		{
			expand();
		}
		buffer[(offset + nbrEntries) & sizeLessOne] = tok;
		nbrEntries++;
	}
	/** Fetch a token from the queue by index
	 * @param idx The index of the token to fetch, where zero is the token at the front of the queue
	 */
	public final Token elementAt(int idx) { 
		return buffer[(offset + idx) & sizeLessOne];
	}
	/** Expand the token buffer by doubling its capacity */
	private final void expand()
	{
		Token[] newBuffer = new Token[buffer.length * 2];
		// Copy the contents to the new buffer
		// Note that this will store the first logical item in the 
		// first physical array element.
                System.arraycopy(buffer, offset, newBuffer, 0, buffer.length - offset);
                System.arraycopy(buffer, 0, newBuffer, buffer.length - offset, offset);
                /*
		for (int i = 0; i < buffer.length; i++)
		{
			newBuffer[i] = elementAt(i);
		}
                */
		// Re-initialize with new contents, keep old nbrEntries
		buffer = newBuffer;
		sizeLessOne = buffer.length - 1;
		offset = 0;
	}
	/** Initialize the queue.
	 * @param size The initial size of the queue
	 */
	private final void init(int size) {
		// Allocate buffer
		buffer = new Token[size];
		// Other initialization
		sizeLessOne = size - 1;
		offset = 0;
		nbrEntries = 0;
	}
	/** Remove token from front of queue */
	public final void removeFirst() { 
		offset = (offset+1) & sizeLessOne;
		nbrEntries--;
	}
}