Base91.java

package de.bwaldvogel.base91;

import java.io.ByteArrayOutputStream;

/**
 * Modified version of Jochaim Henke's original code from
 * http://base91.sourceforge.net/
 * <p/>
 * basE91 encoding/decoding routines
 * <p/>
 * Copyright (c) 2000-2006 Joachim Henke All rights reserved.
 * <p/>
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * <p/>
 * - 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.
 * <p/>
 * 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();
  }
}