brouter/brouter-codec/src/main/java/btools/codec/StatCoderContext.java

package btools.codec;

import java.util.TreeMap;

import btools.util.BitCoderContext;

public final class StatCoderContext extends BitCoderContext
{
  private static TreeMap<String, long[]> statsPerName;
  private long lastbitpos = 0;

  public StatCoderContext( byte[] ab )
  {
    super( ab );
  }

  /**
   * assign the de-/encoded bits since the last call assignBits to the given
   * name. Used for encoding statistics
   * 
   * @see #getBitReport
   */
  public void assignBits( String name )
  {
    long bitpos = getWritingBitPosition();
    if ( statsPerName == null )
    {
      statsPerName = new TreeMap<String, long[]>();
    }
    long[] stats = statsPerName.get( name );
    if ( stats == null )
    {
      stats = new long[2];
      statsPerName.put( name, stats );
    }
    stats[0] += bitpos - lastbitpos;
    stats[1] += 1;
    lastbitpos = bitpos;
  }

  /**
   * Get a textual report on the bit-statistics
   * 
   * @see #assignBits
   */
  public static String getBitReport()
  {
    if ( statsPerName == null )
    {
      return "<empty bit report>";
    }
    StringBuilder sb = new StringBuilder();
    for ( String name : statsPerName.keySet() )
    {
      long[] stats = statsPerName.get( name );
      sb.append( name + " count=" + stats[1] + " bits=" + stats[0] + "\n" );
    }
    statsPerName = null;
    return sb.toString();
  }

  /**
   * encode an unsigned integer with some of of least significant bits
   * considered noisy
   * 
   * @see #decodeNoisyNumber
   */
  public void encodeNoisyNumber( int value, int noisybits )
  {
    if ( value < 0 )
    {
      throw new IllegalArgumentException( "encodeVarBits expects positive value" );
    }
    if ( noisybits > 0 )
    {
      int mask = 0xffffffff >>> ( 32 - noisybits );
      encodeBounded( mask, value & mask );
      value >>= noisybits;
    }
    encodeVarBits( value );
  }

  /**
   * decode an unsigned integer with some of of least significant bits
   * considered noisy
   * 
   * @see #encodeNoisyNumber
   */
  public int decodeNoisyNumber( int noisybits )
  {
    int value = decodeBits( noisybits );
    return value | ( decodeVarBits() << noisybits );
  }

  /**
   * encode a signed integer with some of of least significant bits considered
   * noisy
   * 
   * @see #decodeNoisyDiff
   */
  public void encodeNoisyDiff( int value, int noisybits )
  {
    if ( noisybits > 0 )
    {
      value += 1 << ( noisybits - 1 );
      int mask = 0xffffffff >>> ( 32 - noisybits );
      encodeBounded( mask, value & mask );
      value >>= noisybits;
    }
    encodeVarBits( value < 0 ? -value : value );
    if ( value != 0 )
    {
      encodeBit( value < 0 );
    }
  }

  /**
   * decode a signed integer with some of of least significant bits considered
   * noisy
   * 
   * @see #encodeNoisyDiff
   */
  public int decodeNoisyDiff( int noisybits )
  {
    int value = 0;
    if ( noisybits > 0 )
    {
      value = decodeBits( noisybits ) - ( 1 << ( noisybits - 1 ) );
    }
    int val2 = decodeVarBits() << noisybits;
    if ( val2 != 0 )
    {
      if ( decodeBit() )
      {
        val2 = -val2;
      }
    }
    return value + val2;
  }

  /**
   * encode a signed integer with the typical range and median taken from the
   * predicted value
   * 
   * @see #decodePredictedValue
   */
  public void encodePredictedValue( int value, int predictor )
  {
    int p = predictor < 0 ? -predictor : predictor;
    int noisybits = 0;

    while (p > 2)
    {
      noisybits++;
      p >>= 1;
    }
    encodeNoisyDiff( value - predictor, noisybits );
  }

  /**
   * decode a signed integer with the typical range and median taken from the
   * predicted value
   * 
   * @see #encodePredictedValue
   */
  public int decodePredictedValue( int predictor )
  {
    int p = predictor < 0 ? -predictor : predictor;
    int noisybits = 0;
    while (p > 2)
    {
      noisybits++;
      p >>= 1;
    }
    return predictor + decodeNoisyDiff( noisybits );
  }

  /**
   * encode an integer-array making use of the fact that it is sorted. This is
   * done, starting with the most significant bit, by recursively encoding the
   * number of values with the current bit being 0. This yields an number of
   * bits per value that only depends on the typical distance between subsequent
   * values and also benefits
   * 
   * @param values
   *          the array to encode
   * @param offset
   *          position in this array where to start
   * @param subsize
   *          number of values to encode
   * @param nextbit
   *          bitmask with the most significant bit set to 1
   * @param mask
   *          should be 0
   */
  public void encodeSortedArray( int[] values, int offset, int subsize, int nextbit, int mask )
  {
    if ( subsize == 1 ) // last-choice shortcut
    {
      while (nextbit != 0)
      {
        encodeBit( ( values[offset] & nextbit ) != 0 );
        nextbit >>= 1;
      }
    }
    if ( nextbit == 0 )
    {
      return;
    }

    int data = mask & values[offset];
    mask |= nextbit;

    // count 0-bit-fraction
    int i = offset;
    int end = subsize + offset;
    for ( ; i < end; i++ )
    {
      if ( ( values[i] & mask ) != data )
      {
        break;
      }
    }
    int size1 = i - offset;
    int size2 = subsize - size1;

    encodeBounded( subsize, size1 );
    if ( size1 > 0 )
    {
      encodeSortedArray( values, offset, size1, nextbit >> 1, mask );
    }
    if ( size2 > 0 )
    {
      encodeSortedArray( values, i, size2, nextbit >> 1, mask );
    }
  }

  /**
   * @see #encodeSortedArray
   * 
   * @param values
   *          the array to encode
   * @param offset
   *          position in this array where to start
   * @param subsize
   *          number of values to encode
   * @param nextbit
   *          bitmask with the most significant bit set to 1
   * @param value
   *          should be 0
   */
  public void decodeSortedArray( int[] values, int offset, int subsize, int nextbit, int value )
  {
    if ( subsize == 1 ) // last-choice shortcut
    {
      while (nextbit != 0)
      {
        if ( decodeBit() )
        {
          value |= nextbit;
        }
        nextbit >>= 1;
      }
      values[offset] = value;
      return;
    }
    if ( nextbit == 0 )
    {
      while (subsize-- > 0)
      {
        values[offset++] = value;
      }
      return;
    }

    int size1 = decodeBounded( subsize );
    int size2 = subsize - size1;

    if ( size1 > 0 )
    {
      decodeSortedArray( values, offset, size1, nextbit >> 1, value );
    }
    if ( size2 > 0 )
    {
      decodeSortedArray( values, offset + size1, size2, nextbit >> 1, value | nextbit );
    }
  }

}