gt: 				key = ( key >> 1 ) + ( key & 1 );
context: package ibxm;
  
  import java.io.*;
  
  public class ProTracker {
  	public static boolean is_mod( byte[] header_1084_bytes ) {
  		boolean is_mod;
  		is_mod = false;
  		if( calculate_num_channels( header_1084_bytes ) > 0 ) {
  			is_mod = true;
  		}
  		return is_mod;
  	}
  
  	public static Module load_mod( byte[] header_1084_bytes, DataInput data_input ) throws IOException {
  		int num_channels, channel_idx, panning;
  		int sequence_length, restart_idx, sequence_idx;
  		int num_patterns, pattern_idx, instrument_idx;
  		Module module;
  		num_channels = calculate_num_channels( header_1084_bytes );
  		if( num_channels < 1 ) {
  			throw new IllegalArgumentException( "ProTracker: Unrecognised module format!" );
  		}
  		module = new Module();
  		module.song_title = ascii_text( header_1084_bytes, 0, 20 );
  		module.pal = ( num_channels == 4 );
  		module.global_volume = 64;
  		module.channel_gain = IBXM.FP_ONE * 3 / 8;
  		module.default_speed = 6;
  		module.default_tempo = 125;
  		module.set_num_channels( num_channels );
  		for( channel_idx = 0; channel_idx < num_channels; channel_idx++ ) {
  			panning = 64;
  			if( ( channel_idx & 0x03 ) == 0x01 || ( channel_idx & 0x03 ) == 0x02 ) {
  				panning = 192;
  			}
  			module.set_initial_panning( channel_idx, panning );
  		}
  		sequence_length = header_1084_bytes[ 950 ] & 0x7F;
  		restart_idx = header_1084_bytes[ 951 ] & 0x7F;
  		if( restart_idx >= sequence_length ) {
  			restart_idx = 0;
  		}
  		module.restart_sequence_index = restart_idx;
  		module.set_sequence_length( sequence_length );
  		for( sequence_idx = 0; sequence_idx < sequence_length; sequence_idx++ ) {
  			module.set_sequence( sequence_idx, header_1084_bytes[ 952 + sequence_idx ] & 0x7F );
  		}
  		num_patterns = calculate_num_patterns( header_1084_bytes );
  		module.set_num_patterns( num_patterns );
  		for( pattern_idx = 0; pattern_idx < num_patterns; pattern_idx++ ) {
  			module.set_pattern( pattern_idx, read_mod_pattern( data_input, num_channels ) );
  		}
  		module.set_num_instruments( 31 );
  		for( instrument_idx = 1; instrument_idx <= 31; instrument_idx++ ) {
  			module.set_instrument( instrument_idx, read_mod_instrument( header_1084_bytes, instrument_idx, data_input ) );
  		}
  		return module;
  	}
  
  	private static int calculate_num_patterns( byte[] module_header ) {
  		int num_patterns, order_entry, pattern_idx;
  		num_patterns = 0;
  		for( pattern_idx = 0; pattern_idx < 128; pattern_idx++ ) {
  			order_entry = module_header[ 952 + pattern_idx ] & 0x7F;
  			if( order_entry >= num_patterns ) {
  				num_patterns = order_entry + 1;
  			}
  		}
  		return num_patterns;
  	}
  	
  	private static int calculate_num_channels( byte[] module_header ) {
  		int num_channels;
  		switch( ( module_header[ 1082 ] << 8 ) | module_header[ 1083 ] ) {
  			case 0x4b2e: /* M.K. */
  			case 0x4b21: /* M!K! */
  			case 0x542e: /* N.T. */
  			case 0x5434: /* FLT4 */
  				num_channels = 4;
  				break;
  			case 0x484e: /* xCHN */
  				num_channels = module_header[ 1080 ] - 48;
  				break;
  			case 0x4348: /* xxCH */
  				num_channels = ( ( module_header[ 1080 ] - 48 ) * 10 ) + ( module_header[ 1081 ] - 48 );
  				break;
  			default:
  				/* Not recognised. */
  				num_channels = 0;
  				break;
  		}
  		return num_channels;
  	}
  
  	private static Pattern read_mod_pattern( DataInput data_input, int num_channels ) throws IOException {
  		int input_idx, output_idx;
  		int period, instrument, effect, effect_param;
  		Pattern pattern;
  		byte[] input_pattern_data, output_pattern_data;
  		pattern = new Pattern();
  		pattern.num_rows = 64;
  		input_pattern_data = new byte[ 64 * num_channels * 4 ];
  		output_pattern_data = new byte[ 64 * num_channels * 5 ];
  		data_input.readFully( input_pattern_data );
  		input_idx = 0;
  		output_idx = 0;
  		while( input_idx < input_pattern_data.length ) {
  			period = ( input_pattern_data[ input_idx ] & 0x0F ) << 8;
  			period = period | ( input_pattern_data[ input_idx + 1 ] & 0xFF );
  			output_pattern_data[ output_idx ] = to_key( period );
  			instrument = input_pattern_data[ input_idx ] & 0x10;
  			instrument = instrument | ( ( input_pattern_data[ input_idx + 2 ] & 0xF0 ) >> 4 );
  			output_pattern_data[ output_idx + 1 ] = ( byte ) instrument;
  			effect = input_pattern_data[ input_idx + 2 ] & 0x0F;
  			effect_param = input_pattern_data[ input_idx + 3 ] & 0xFF;
  			if( effect == 0x01 && effect_param == 0 ) {
  				/* Portamento up of zero has no effect. */
  				effect = 0;
  			}
  			if( effect == 0x02 && effect_param == 0 ) {
  				/* Portamento down of zero has no effect. */
  				effect = 0;
  			}
  			if( effect == 0x08 && num_channels == 4 ) {
  				/* Some Amiga mods use effect 0x08 for reasons other than panning.*/
  				effect = 0;
  				effect_param = 0;
  			}
  			if( effect == 0x0A && effect_param == 0 ) {
  				/* Volume slide of zero has no effect.*/
  				effect = 0;
  			}
  			if( effect == 0x05 && effect_param == 0 ) {
  				/* Porta + Volume slide of zero has no effect.*/
  				effect = 0x03;
  			}
  			if( effect == 0x06 && effect_param == 0 ) {
  				/* Vibrato + Volume slide of zero has no effect.*/
  				effect = 0x04;
  			}
  			output_pattern_data[ output_idx + 3 ] = ( byte ) effect;
  			output_pattern_data[ output_idx + 4 ] = ( byte ) effect_param;
  			input_idx += 4;
  			output_idx += 5;
  		}
  		pattern.set_pattern_data( output_pattern_data );
  		return pattern;
  	}
  
  	private static Instrument read_mod_instrument( byte[] mod_header, int idx, DataInput data_input ) throws IOException  {
  		int header_offset, sample_data_length;
  		int loop_start, loop_length, sample_idx, fine_tune;
  		Instrument instrument;
  		Sample sample;
  		byte[] raw_sample_data;
  		short[] sample_data;
  		header_offset = ( idx - 1 ) * 30 + 20;
  		instrument = new Instrument();
  		instrument.name = ascii_text( mod_header, header_offset, 22 );
  		sample = new Sample();
  		sample_data_length = unsigned_short_be( mod_header, header_offset + 22 ) << 1;
  		fine_tune = mod_header[ header_offset + 24 ] & 0x0F;
  		if( fine_tune > 7 ) {
  			fine_tune -= 16;
  		}
  		sample.transpose = ( fine_tune << IBXM.FP_SHIFT ) / 96;
  		sample.volume = mod_header[ header_offset + 25 ] & 0x7F;
  		loop_start = unsigned_short_be( mod_header, header_offset + 26 ) << 1;
  		loop_length = unsigned_short_be( mod_header, header_offset + 28 ) << 1;
  		if( loop_length < 4 ) {
  			loop_length = 0;
  		}
  		raw_sample_data = new byte[ sample_data_length ];
  		sample_data = new short[ sample_data_length ];
  		try {
  			data_input.readFully( raw_sample_data );
  		} catch( EOFException e ) {
  			System.out.println( "ProTracker: Instrument " + idx + " has samples missing." );
  		}
  		for( sample_idx = 0; sample_idx < raw_sample_data.length; sample_idx++ ) {
  			sample_data[ sample_idx ] = ( short ) ( raw_sample_data[ sample_idx ] << 8 );
  		}
  		sample.set_sample_data( sample_data, loop_start, loop_length, false );
  		instrument.set_num_samples( 1 );
  		instrument.set_sample( 0, sample );
  		return instrument;
  	}
  	
  	private static byte to_key( int period ) {
  		int oct, key;
  		if( period < 32 ) {
  			key = 0;
  		} else {
  			oct = LogTable.log_2( 7256 ) - LogTable.log_2( period );
  			if( oct < 0 ) {
  				key = 0;
  			} else {
  				key = oct * 12;
  				key = key >> ( IBXM.FP_SHIFT - 1 );
  