Base91.java

package net.solarnetwork.io;

import java.io.ByteArrayOutputStream;

/**
 * Modified version of Jochaim Henke's original code from
 * http://base91.sourceforge.net/
 * 
 * basE91 encoding/decoding routines
 * 
 * Copyright (c) 2000-2006 Joachim Henke All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * - Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer. - Redistributions in binary
 * form must reproduce the above copyright notice, this list of conditions and
 * the following disclaimer in the documentation and/or other materials provided
 * with the distribution. - Neither the name of Joachim Henke nor the names of
 * his contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * @author Joachim Henke (Original version)
 * @author Benedikt Waldvogel (Modifications)
 */
public class Base91 {

	public static final byte[] ENCODING_TABLE;
	private static final byte[] DECODING_TABLE;
	private static final int BASE;
	private static final float AVERAGE_ENCODING_RATIO = 1.2297f;

	static {
		String ts = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%&()*+,./:;<=>?@[]^_`{|}~\"";
		ENCODING_TABLE = ts.getBytes();
		BASE = ENCODING_TABLE.length;

		DECODING_TABLE = new byte[256];
		for ( int i = 0; i < 256; ++i )
			DECODING_TABLE[i] = -1;

		for ( int i = 0; i < BASE; ++i )
			DECODING_TABLE[ENCODING_TABLE[i]] = (byte) i;
	}

	public static byte[] encode(byte[] data) {

		int estimatedSize = (int) Math.ceil(data.length * AVERAGE_ENCODING_RATIO);
		ByteArrayOutputStream output = new ByteArrayOutputStream(estimatedSize);

		int ebq = 0;
		int en = 0;
		for ( int i = 0; i < data.length; ++i ) {
			ebq |= (data[i] & 255) << en;
			en += 8;
			if ( en > 13 ) {
				int ev = ebq & 8191;

				if ( ev > 88 ) {
					ebq >>= 13;
					en -= 13;
				} else {
					ev = ebq & 16383;
					ebq >>= 14;
					en -= 14;
				}
				output.write(ENCODING_TABLE[ev % BASE]);
				output.write(ENCODING_TABLE[ev / BASE]);
			}
		}

		if ( en > 0 ) {
			output.write(ENCODING_TABLE[ebq % BASE]);
			if ( en > 7 || ebq > 90 ) {
				output.write(ENCODING_TABLE[ebq / BASE]);
			}
		}

		return output.toByteArray();
	}

	public static byte[] decode(byte[] data) {

		// if (data.length == 0)
		// return new byte[] {};

		int dbq = 0;
		int dn = 0;
		int dv = -1;

		int estimatedSize = Math.round(data.length / AVERAGE_ENCODING_RATIO);
		ByteArrayOutputStream output = new ByteArrayOutputStream(estimatedSize);

		for ( int i = 0; i < data.length; ++i ) {
			if ( DECODING_TABLE[data[i]] == -1 )
				continue;
			if ( dv == -1 )
				dv = DECODING_TABLE[data[i]];
			else {
				dv += DECODING_TABLE[data[i]] * BASE;
				dbq |= dv << dn;
				dn += (dv & 8191) > 88 ? 13 : 14;
				do {
					output.write((byte) dbq);
					dbq >>= 8;
					dn -= 8;
				} while ( dn > 7 );
				dv = -1;
			}
		}

		if ( dv != -1 ) {
			output.write((byte) (dbq | dv << dn));
		}

		return output.toByteArray();
	}
}