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 <code>buffer[start]</code>, …,
* <code>buffer[(start+len+buffer.length-1)%buffer.length]</code>
*/
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 <code>b[offset]</code>, … <code>b[offset+length-1]</code> 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;
}
}