Add a decoder for Simulink derived MAT files.

/*

 * Copyright 2014 Matthew Dawson <matthew@mjdsystems.ca>

 */

package ca.mjdsystems.jmatio.io;

import java.io.EOFException;

import java.io.IOException;

import java.io.InputStream;

import java.util.HashMap;

import java.util.Map;

/** This class decodes the Simulink base64 representation of a MAT file.

 *

 * @author Matthew Dawson <matthew@mjdsystems.ca>

 */

public class SimulinkDecoder extends InputStream

{

    public SimulinkDecoder(String input)

    {

        this.input = input.getBytes();

        for (byte i = 0; i < 64; ++i) {

            decoderRing.put((byte)(i + ' '), i);

        }

        System.out.println("S " + input.length() + " B " + this.input.length);

    }

    @Override

    public int read() throws IOException

    {

        try {

            int ret;

            switch (pos % 4) {

                case 0: {

                    byte first = decoderRing.get(input[pos++]);

                    byte second = decoderRing.get(input[pos++]);

                    ret = (first << 2) | (second >> 4);

                    leftover = (byte) (second & 0x0f);

                    break;

                }

                case 2: {

                    byte next = decoderRing.get(input[pos++]);

                    ret = (leftover << 4) | (next >> 2);

                    leftover = (byte) (next & 0x03);

                    break;

                }

                case 3: {

                    byte next = decoderRing.get(input[pos++]);

                    ret = (leftover << 6) | next;

                    break;

                }

                default:

                    throw new RuntimeException("Case " + (pos % 4));

            }

            return ret;

        } catch (ArrayIndexOutOfBoundsException ex) {

            pos = -1; // Ensure that the exception will be re-thrown, avoiding a buffer overflow.

            throw new EOFException("No more bytes!");

        }

    }

    private final byte[] input;

    private int pos;

    private byte leftover;

    final private Map<Byte, Byte> decoderRing = new HashMap<Byte, Byte>();

}