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

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;


public final class DiffCoderDataInputStream extends DataInputStream
{
  private long[] lastValues = new long[10];
	
  public DiffCoderDataInputStream( InputStream is )
  {
	 super( is );
  }
  
  public long readDiffed( int idx ) throws IOException
  {
	  long d = readSigned();
	  long  v = lastValues[idx] + d;
	  lastValues[idx] = v;
	  return v;
  }

  public long readSigned() throws IOException
  {
	  long v = readUnsigned();
	  return ( v & 1 ) == 0 ? v >> 1 : -(v >> 1 );
  }

  public long readUnsigned() throws IOException
  {
		long v = 0;
		int shift = 0;
		for(;;)
		{
		  long i7 = readByte() & 0xff;
		  v |= (( i7 & 0x7f ) << shift);
		  if ( ( i7 & 0x80 ) == 0 ) break;
		  shift += 7;
		}
		return v;
  }
}