suballocatedintvector.java

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/*
 * The Apache Software License, Version 1.1
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 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
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 *       "This product includes software developed by the
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
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 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
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package org.apache.xml.utils;

/**
 * <meta name="usage" content="internal"/>
 * A very simple table that stores a list of int. Very similar API to our
 * IntVector class (same API); different internal storage.
 * 
 * This version uses an array-of-arrays solution. Read/write access is thus
 * a bit slower than the simple IntVector, and basic storage is a trifle
 * higher due to the top-level array -- but appending is O(1) fast rather
 * than O(N**2) slow, which will swamp those costs in situations where
 * long vectors are being built up.
 * 
 * Known issues:
 * 
 * Some methods are private because they haven't yet been tested properly.
 *
 * Retrieval performance is critical, since this is used at the core
 * of the DTM model. (Append performance is almost as important.)
 * That's pushing me toward just letting reads from unset indices
 * throw exceptions or return stale data; safer behavior would have
 * performance costs.
 * */
public class SuballocatedIntVector
{
  /** Size of blocks to allocate          */
  protected int m_blocksize;

  /** Bitwise addressing (much faster than div/remainder */
  protected int m_SHIFT, m_MASK;
  
  /** Number of blocks to (over)allocate by */
  protected  int m_numblocks=32;
  
  /** Array of arrays of ints          */
  protected int m_map[][];

  /** Number of ints in array          */
  protected int m_firstFree = 0;

  /** "Shortcut" handle to m_map[0]. Surprisingly helpful for short vectors. */
  protected int m_map0[];


  /**
   * Default constructor.  Note that the default
   * block size is currently 2K, which may be overkill for
   * small lists and undershootng for large ones.
   */
  public SuballocatedIntVector()
  {
    this(2048);
  }

  /**
   * Construct a IntVector, using the given block size. For
   * efficiency, we will round the requested size off to a power of
   * two.
   *
   * @param blocksize Size of block to allocate
   * */
  public SuballocatedIntVector(int blocksize)
  {
    //m_blocksize = blocksize;
    for(m_SHIFT=0;0!=(blocksize>>>=1);++m_SHIFT)
      ;
    m_blocksize=1<<m_SHIFT;
    m_MASK=m_blocksize-1;
		
    m_map0=new int[m_blocksize];
    m_map = new int[m_numblocks][];
    m_map[0]=m_map0;
  }
	
  /** We never _did_ use the increasesize parameter, so I'm phasing
   * this constructor out.
   *
   * @deprecated use SuballocatedIntVector(int)
   * @see SuballocatedIntVector(int)
   * */
  public SuballocatedIntVector(int blocksize,int increasesize)
  {
    this(blocksize);
  }

  /**
   * Get the length of the list.
   *
   * @return length of the list
   */
  public int size()
  {
    return m_firstFree;
  }
  
  /**
   * Set the length of the list. This will only work to truncate the list, and
   * even then it has not been heavily tested and may not be trustworthy.
   *
   * @return length of the list
   */
  public void setSize(int sz)
  {
    if(m_firstFree>sz) // Whups; had that backward!
      m_firstFree = sz;
  }

  /**
   * Append a int onto the vector.
   *
   * @param value Int to add to the list 
   */
  public  void addElement(int value)
  {
    if(m_firstFree<m_blocksize)
      m_map0[m_firstFree++]=value;
    else
    {
      // Growing the outer array should be rare. We initialize to a
      // total of m_blocksize squared elements, which at the default
      // size is 4M integers... and we grow by at least that much each
      // time.  However, attempts to microoptimize for this (assume
      // long enough and catch exceptions) yield no noticable
      // improvement.

      int index=m_firstFree>>>m_SHIFT;
      int offset=m_firstFree&m_MASK;

      if(index>=m_map.length)
      {
	int newsize=index+m_numblocks;
	int[][] newMap=new int[newsize][];
	System.arraycopy(m_map, 0, newMap, 0, m_map.length);
	m_map=newMap;
      }
      int[] block=m_map[index];
      if(null==block)
	block=m_map[index]=new int[m_blocksize];
      block[offset]=value;

      ++m_firstFree;
    }
  }
  
  /**
   * Append several int values onto the vector.
   *
   * @param value Int to add to the list 
   */
  private  void addElements(int value, int numberOfElements)
  {
    if(m_firstFree+numberOfElements<m_blocksize)
      for (int i = 0; i < numberOfElements; i++) 
      {
        m_map0[m_firstFree++]=value;
      }
    else
    {
      int index=m_firstFree>>>m_SHIFT;
      int offset=m_firstFree&m_MASK;
      m_firstFree+=numberOfElements;
      while( numberOfElements>0)
      {
        if(index>=m_map.length)
        {
          int newsize=index+m_numblocks;
          int[][] newMap=new int[newsize][];
          System.arraycopy(m_map, 0, newMap, 0, m_map.length);
          m_map=newMap;
        }
        int[] block=m_map[index];
        if(null==block)
          block=m_map[index]=new int[m_blocksize];
        int copied=(m_blocksize-offset < numberOfElements)
          ? m_blocksize-offset : numberOfElements;
        numberOfElements-=copied;
        while(copied-- > 0)
          block[offset++]=value;

        ++index;offset=0;
      }
    }
  }
  
  /**
   * Append several slots onto the vector, but do not set the values.
   * Note: "Not Set" means the value is unspecified.
   *
   * @param value Int to add to the list 
   */
  private  void addElements(int numberOfElements)
  {
    int newlen=m_firstFree+numberOfElements;
    if(newlen>m_blocksize)
    {
      int index=m_firstFree>>>m_SHIFT;
      int newindex=(m_firstFree+numberOfElements)>>>m_SHIFT;
      for(int i=index+1;i<=newindex;++i)
        m_map[i]=new int[m_blocksize];
    }
    m_firstFree=newlen;
  }
  
  /**
   * Inserts the specified node in this vector at the specified index.
   * Each component in this vector with an index greater or equal to
   * the specified index is shifted upward to have an index one greater
   * than the value it had previously.
   *
   * Insertion may be an EXPENSIVE operation!
   *
   * @param value Int to insert
   * @param at Index of where to insert 
   */
  private  void insertElementAt(int value, int at)
  {
    if(at==m_firstFree)
      addElement(value);
    else if (at>m_firstFree)
    {
      int index=at>>>m_SHIFT;