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Lib-Cross-Java for the Connected Device Configuration v1.1.2
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/*
 * libxjava -- utility library for cross-Java-platform development
 *             Lib-Cross-Java CDC
 *
 * Copyright (c) 2010 Marcel Patzlaff ([email protected])
 *
 * 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 3 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 library.  If not, see .
 */

package com.github.libxjava.util;


/**
 * Simple ring buffer set.
 * It uses the standard Java hash mechanism to detect already
 * inserted objects.
 * 
 * @author Marcel Patzlaff
 * @version libxjava-cdc - 0.3
 */
public class HashRingSet {
    private static final int LOAD_FACTOR = 75;
    
    private final HashRingSetEntry[] _table;
    private final Object[] _content;
    
    private int _count;
    private int _pos;
    
    public HashRingSet(int capacity) {
        _content= new Object[capacity];
        _table= new HashRingSetEntry[(100 * capacity) / LOAD_FACTOR];
        _count= 0;
        _pos= 0;
    }
    
    public boolean add(Object obj) {
        synchronized(_content) {
            int hash= obj.hashCode();
            int index= (hash & 0x7FFFFFFF) % _table.length;
            for (HashRingSetEntry e = _table[index] ; e != null ; e = e.next) {
                if ((e.hash == hash) && _content[e.index].equals(obj)) {
                    return false;
                }
            }
            
            HashRingSetEntry e= new HashRingSetEntry();
            e.hash= hash;
            e.index= _pos;
            e.next= _table[index];
            _table[index]= e;

            if(_count >= _content.length) {
                if(!freePosition()) {
                    throw new Error("implementation bug");
                }
            } else {
                ++_count;
            }
            
            _content[_pos]= obj;
            _pos= (_pos + 1) % _content.length;
            
            return true;
        }
    }
    
    public boolean contains(Object obj) {
        synchronized(_content) {
            int hash= obj.hashCode();
            int index= (hash & 0x7FFFFFFF) % _table.length;
            for (HashRingSetEntry e = _table[index] ; e != null ; e = e.next) {
                if ((e.hash == hash) && _content[e.index].equals(obj)) {
                    return true;
                }
            }
            
            return false;
        }
    }
    
    public String toString() {
        synchronized(_content) {
            StringBuffer buffer= new StringBuffer();
            buffer.append('[');
            final int preLast= _count - 1;
            for(int c= 0, i= _content.length + _pos - _count; c <= preLast; ++c, ++i) {
                buffer.append(String.valueOf(_content[i % _content.length]));
                
                if(c < preLast) {
                    buffer.append(", ");
                }
            }
            
            buffer.append(']');
            return buffer.toString();
        }
    }
        
    private boolean freePosition() {
        int hash= _content[_pos].hashCode();
        int tableIndex= (hash & 0x7FFFFFFF) % _table.length;
        for (HashRingSetEntry e= _table[tableIndex], prev= null; e != null; prev=e, e= e.next) {
            if ((e.hash == hash) && (e.index == _pos)) {
                if (prev != null) {
                    prev.next = e.next;
                } else {
                    _table[tableIndex] = e.next;
                }
                
                return true;
            }
        }
        
        return false;
    }
}

class HashRingSetEntry {
    int index;
    int hash;
    HashRingSetEntry next;
}