/**
 * DataOutputStream extended by varlength diff coding
 *
 * @author ab
 */
package btools.util;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;


public final class DiffCoderDataOutputStream extends DataOutputStream
{
  private long[] lastValues = new long[10];
	
  public DiffCoderDataOutputStream( OutputStream os )
  {
	 super( os );
  }
  
  public void writeDiffed( long v, int idx ) throws IOException
  {
	  long d = v - lastValues[idx];
	  lastValues[idx] = v;
	  writeSigned( d );
  }

  public void writeSigned( long v ) throws IOException
  {
    writeUnsigned( v < 0 ? ( (-v) << 1 ) | 1 : v << 1 );
  }

  public void writeUnsigned( long v ) throws IOException
  {
	do
	{
	  long i7 = v & 0x7f;
	  v >>= 7;
	  if ( v != 0 ) i7 |= 0x80;
	  writeByte( (byte)( i7 & 0xff ) );
	}
	while( v != 0 );
  }
}