brouter/brouter-util/src/main/java/btools/util/CompactLongMap.java

package btools.util;

import java.util.ArrayList;

/**
 * Memory efficient Map to map a long-key to an object-value
 *
 * Implementation is such that basically the 12 bytes
 * per entry is allocated that's needed to store
 * a long- and an object-value.
 * This class does not implement the Map interface
 * because it's not complete (remove() is not implemented,
 * CompactLongMap can only grow.)
 *
 * @author ab
 */
public class CompactLongMap<V>
{
  private long[][] al;
  private int[] pa;
  private int size = 0;
  private int _maxKeepExponent = 14; // the maximum exponent to keep the invalid arrays

  protected V value_in;
  protected V value_out;

  protected static final int MAXLISTS = 31; // enough for size Integer.MAX_VALUE
  private static boolean earlyDuplicateCheck;

  public CompactLongMap()
  {
    // pointer array
    pa = new int[MAXLISTS];

    // allocate key lists
    al = new long[MAXLISTS][];
    al[0] = new long[1]; // make the first array (the transient buffer)

    // same for the values
    vla = new Object[MAXLISTS][];
    vla[0] = new Object[1];

    earlyDuplicateCheck = Boolean.getBoolean( "earlyDuplicateCheck" );
  }


  /*
   *
   * The Map extension:
   * next 5 protected methods are needed to implement value-support
   * overwrite them all to support value structures other than the
   * long-values implemented here as a sample.
   *
   * Furthermore, put() and get() method need to be implemented
   * to access the values.
   *
   * Note that this map does not behave exactly like java.util.Map
   * - put(..) with already existing key throws exception
   * - get(..) with non-existing key thros exception
   *
   * If you have keys that cannot easily be mapped on long's, use
   * a hash-function to do the mapping. But note that, in comparison
   * to java.util.HashMap, in that case the keys itself are not saved,
   * only the hash-values, so you need to be sure that random duplicate
   * hashs are either excluded by the structure of your data or that
   * you can handle the possible IllegalArgumentException
   *
   */

  private Object[][] vla; // value list array


  public boolean put( long id, V value )
  {
    try
    {    
      value_in = value;
      if ( contains( id, true ) )
      {
        return true;
      }
      vla[0][0] = value;
      _add( id );
      return false;
    }
    finally
    {
      value_in = null;
      value_out = null;
    }
  }

  /**
   * Same as put( id, value ) but duplicate check
   * is skipped for performance. Be aware that you
   * can get a duplicate exception later on if the
   * map is restructured!
   * with System parameter earlyDuplicateCheck=true you
   * can enforce the early duplicate check for debugging
   *
   * @param id the key to insert
   * @param value the value to insert object
   * @exception IllegalArgumentException for duplicates if enabled
   */
  public void fastPut( long id, V value )
  {
    if ( earlyDuplicateCheck && contains( id ) )
    {
      throw new IllegalArgumentException( "duplicate key found in early check: " + id );
    }
    vla[0][0] = value;
    _add( id );
  }

  /**
   * Get the value for the given id
   * @param id the key to query
   * @return the object, or null if id not known
   */
  public V get( long id )
  {
    try
    {
      if ( contains( id, false ) )
      {
        return value_out;
      }
      return null;
    }
    finally
    {
      value_out = null;
    }
  }


  /**
   * @return the number of entries in this map
   */
  public int size()
  {
    return size;
  }


  private boolean _add( long id )
  {
    if ( size == Integer.MAX_VALUE )
    {
      throw new IllegalArgumentException( "cannot grow beyond size Integer.MAX_VALUE" );
    }

    // put the new entry in the first array
    al[0][0] = id;

    // determine the first empty array
    int bp = size++; // treat size as bitpattern
    int idx = 1;
    int n = 1;

    pa[0] = 1;
    pa[1] = 1;

    while ( (bp&1) == 1 )
    {
      bp >>= 1;
      pa[idx++] = n;
      n <<= 1;
    }

    // create it if not existant
    if ( al[idx] == null )
    {
      al[idx] = new long[n];
      vla[idx] = new Object[n];
    }

    // now merge the contents of arrays 0...idx-1 into idx
    while ( n > 0 )
    {
      long maxId = 0;
      int maxIdx = -1;

      for ( int i=0; i<idx; i++ )
      {
        int p = pa[i];
        if ( p > 0 )
        {
          long currentId = al[i][p-1];
          if ( maxIdx < 0 || currentId > maxId )
          {
            maxIdx = i;
            maxId = currentId;
          }
        }
      }

      // current maximum found, copy to target array
      if ( n < al[idx].length && maxId == al[idx][n] )
      {
        throw new IllegalArgumentException( "duplicate key found in late check: " + maxId );
      }
      --n;
      al[idx][n] = maxId;
      vla[idx][n] = vla[maxIdx][pa[maxIdx]-1];

      --pa[maxIdx];
    }

    // de-allocate empty arrays of a certain size (fix at 64kByte)
    while ( idx-- > _maxKeepExponent )
    {
      al[idx] = null;
      vla[idx] = null;
    }

    return false;
  }

  /**
   * @return true if "id" is contained in this set.
   */
  public boolean contains( long id )
  {
    try
    {
      return contains( id, false );
    }
    finally
    {
      value_out = null;
    }
  }

  protected boolean contains( long id, boolean doPut )
  {
    // determine the first empty array
    int bp = size; // treat size as bitpattern
    int idx = 1;

    while ( bp != 0 )
    {
      if ( (bp&1) == 1 )
      {
        // array at idx is valid, check
        if ( contains( idx, id, doPut ) )
        {
          return true;
        }
      }
      idx++;
      bp >>= 1;
    }
    return false;
  }


  // does sorted array "a" contain "id" ?
  private boolean contains( int idx, long id, boolean doPut )
  {
    long[] a = al[idx];
    int offset = a.length;
    int n = 0;

    while ( (offset >>= 1) > 0 )
    {
      int nn = n + offset;
      if ( a[nn] <= id )
      {
        n = nn;
      }
    }
    if ( a[n] == id )
    {
      value_out = (V)vla[idx][n];
      if ( doPut ) vla[idx][n] = value_in;
      return true;
    }
    return false;
  }

  protected void moveToFrozenArrays( long[] faid, ArrayList<V> flv )
  {
    for( int i=1; i<MAXLISTS; i++ )
    {
      pa[i] = 0;
    }

    for( int ti = 0; ti < size; ti++ ) // target-index
    {
      int bp = size; // treat size as bitpattern
      int minIdx = -1;
      long minId = 0;
      int idx = 1;
      while ( bp != 0 )
      {
        if ( (bp&1) == 1 )
        {
          int p = pa[idx];
          if ( p < al[idx].length )
          {
            long currentId = al[idx][p];
            if ( minIdx < 0 || currentId < minId )
            {
              minIdx = idx;
              minId = currentId;
            }
          }
        }
        idx++;
        bp >>= 1;
      }
      faid[ti] = minId;
      flv.add( (V)vla[minIdx][pa[minIdx]] );
      pa[minIdx]++;

      if ( ti > 0 && faid[ti-1] == minId )
      {
        throw new IllegalArgumentException( "duplicate key found in late check: " + minId );
      }
    }

    // free the non-frozen arrays
    al = null;
    vla = null;
  }

}