DecoderFrontEnd.java

/*
 * Copyright 2005-2015 by BerryWorks Software, LLC. All rights reserved.
 *
 * This file is part of EDIReader. You may obtain a license for its use directly from
 * BerryWorks Software, and you may also choose to use this software under the terms of the
 * GPL version 3. Other products in the EDIReader software suite are available only by licensing
 * with BerryWorks. Only those files bearing the GPL statement below are available under the GPL.
 *
 * EDIReader is free software: you can redistribute it and/or modify it under the terms of the
 * GNU General Public License as published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * EDIReader is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with EDIReader.  If not,
 * see <http://www.gnu.org/licenses/>.
 */

package com.berryworks.edireader.util.base64;

/**
 * This class is part of the internal implementation
 * of the base-64 encoding/decoding.
 */
public abstract class DecoderFrontEnd extends AbstractEncoderDecoder {

    private static final int capitalA = 65;
    private static final int capitalZ = 90;
    private static final int lowerCaseA = 97;
    private static final int lowerCaseZ = 122;
    private static final int digit0 = 48;
    private static final int digit9 = 57;
    private static final int plus = 43;
    private static final int slash = 47;

    @Override
    public void consume(byte b) {

        /**
         * First map the A-Z, a-z. 0-9, +/ ASCII chars into
         * the corresponding 6-bit binary values.
         * If we encounter something other than one of these, just return.
         * Note that the "=" used as padding is also deliberately ignored.
         */
        int unsignedInt = b & 127;
        if (unsignedInt >= capitalA) {
            if (unsignedInt <= capitalZ) unsignedInt -= capitalA;
            else if (unsignedInt >= lowerCaseA) {
                if (unsignedInt <= lowerCaseZ) unsignedInt -= lowerCaseA - 26;
                else return;
            } else return;
        } else if (unsignedInt >= digit0)
            if (unsignedInt <= digit9) unsignedInt -= digit0 - 52;
            else return;
        else if (unsignedInt == plus) unsignedInt = 62;
        else if (unsignedInt == slash) unsignedInt = 63;
        else return;

        /**
         * Now emit this result as a single byte or as two bytes
         * depending upon what state we are in.
         */
        switch (state) {
            default:
            case STATE62:
                emit((byte) unsignedInt);
                state = STATE24;
                break;
            case STATE24:
                emit((byte) (unsignedInt >>> 4));
                emit((byte) (unsignedInt & 15));
                state = STATE42;
                break;
            case STATE42:
                emit((byte) (unsignedInt >>> 2));
                emit((byte) (unsignedInt & 3));
                state = STATE66;
                break;
            case STATE66:
                emit((byte) unsignedInt);
                state = STATE62;
                break;
        }
    }
}