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Bobo is a Faceted Search implementation written purely in Java, an extension of Apache Lucene

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/**
 *
 */
package com.browseengine.bobo.util;

import java.util.ArrayList;

public class BigIntBuffer {
  private static final int PAGESIZE = 1024;
  private static final int MASK = 0x3FF;
  private static final int SHIFT = 10;

  private final ArrayList _buffer;
  private int _allocSize;
  private int _mark;

  public BigIntBuffer() {
    _buffer = new ArrayList();
    _allocSize = 0;
    _mark = 0;
  }

  public int alloc(int size) {
    if (size > PAGESIZE) throw new IllegalArgumentException("size too big");

    if ((_mark + size) > _allocSize) {
      int[] page = new int[PAGESIZE];
      _buffer.add(page);
      _allocSize += PAGESIZE;
    }
    int ptr = _mark;
    _mark += size;

    return ptr;
  }

  public void reset() {
    _mark = 0;
  }

  public void set(int ptr, int val) {
    int[] page = _buffer.get(ptr >> SHIFT);
    page[ptr & MASK] = val;
  }

  public int get(int ptr) {
    int[] page = _buffer.get(ptr >> SHIFT);
    return page[ptr & MASK];
  }
}