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Blazegraph Modifications to the DSI utils. This are forked from version 1.10.0 under LGPLv2.1.
There is a newer version: 2.1.4
package it.unimi.dsi.util;

/*		 
 * DSI utilities
 *
 * Copyright (C) 2006-2009 Paolo Boldi 
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 2.1 of the License, or (at your option)
 *  any later version.
 *
 *  This library is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 *  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 */

import java.util.Arrays;

/** A circular char buffer, that can be used to implement a sliding
 *  window over a text. The buffer has a maximum size, fixed at construction time. As new characters
 *  are {@linkplain #add(char[], int, int) added}, the oldest ones are discarded if necessary. At all
 *  times, the number of available characters present in the buffer is {@link #size()} (it will never be larger
 *  than the buffer size). The characters present in the buffer are provided through the {@link #toCharArray(char[], int, int)}
 *  method and alike.
 */
public class CircularCharArrayBuffer {
	private static final boolean DEBUG = false;
	
	/** The buffer. */
	private final char[] buffer;
	/** The number of character available in the buffer. */
	private int len;
	/** The index of the first character available in the buffer:
	 *  hence the available characters are buffer[start], …,
	 *  buffer[(start+len+buffer.length-1)%buffer.length]
	 */
	private int start;
	
	/** Creates a new circular buffer.
	 * 
	 * @param maxChar the buffer size.
	 */
	public CircularCharArrayBuffer( int maxChar ) {
		buffer = new char[ maxChar ];
		if ( DEBUG ) Arrays.fill( buffer, ' ' );
	}
	
	/** Adds the characters b[offset], … b[offset+length-1] to the
	 *  buffer (possibly just the last ones, and possibly discarding the oldest characters in the buffer).
	 * 
	 * @param b the array whence characters are copied.
	 * @param offset the starting point.
	 * @param length the (maximum) number of characters to be copied.
	 */
	public void add( char[] b, int offset, int length ) {
		if ( buffer.length == 0 ) return;
		int toBeCopied = length;
		if ( DEBUG ) System.out.println( "Called add(" + new String( b, offset, toBeCopied ) + ")" );
		if ( toBeCopied > buffer.length )  {
			offset += toBeCopied - buffer.length;
			toBeCopied = buffer.length;
		}
		// Now length contains the number of bytes to be _really_ copied
		int toEnd = Math.min( toBeCopied, buffer.length - ( start + len ) % buffer.length );
		// toEnd is the number of bytes that are free from the first free position to the end of the buffer
		System.arraycopy( b, offset, buffer, ( start + len ) % buffer.length, toEnd );
		if ( toBeCopied > toEnd ) {
			// length - toEnd is the number of other characters remaining
			System.arraycopy( b, offset + toEnd, buffer, 0, toBeCopied - toEnd );
		}
		if ( toBeCopied > buffer.length - len ) {
			start = ( start + toBeCopied + len ) % buffer.length;
		}
		// After filling, length is just buffer.length
		len = Math.min( buffer.length, len + toBeCopied );
		
	}
	
	/** Copies the content of the buffer to an array.
	 * 
	 * @param b the buffer where the content is to be copied.
	 * @param offset the starting index where copy should start from.
	 * @param length the maximum number of characters to be copied.
	 */
	public void toCharArray( char[] b, int offset, int length ) {
		if ( buffer.length == 0 ) return;
		int t = Math.min( length, len );
		int toEnd = Math.min( t, buffer.length - start );
		System.arraycopy( buffer, start, b, offset, toEnd );
		if ( toEnd < t ) System.arraycopy( buffer, 0, b, offset + toEnd, t - toEnd );
	}
	
	/** Copies the content of the buffer to an array.
	 * 
	 * @param b the buffer where the content is to be copied.
	 */
	public void toCharArray( char[] b ) {
		toCharArray( b, 0, b.length );
	}
	
	/** Returns a new array containing a copy of the buffer content.
	 * 
	 * @return a copy of the buffer content.
	 */
	public char[] toCharArray() {
		char[] b = new char[ size() ];
		toCharArray( b );
		return b;
	}
	
	/** The number of characters present in the buffer.
	 * 
	 * @return the number of characters present in the buffer.
	 */
	public int size() {
		return len;
	}
	
	/** Clears the buffer content, before reuse. */
	public void clear() {
		len = 0;
	}
	
}