MoveToFront.java

/*
 * Copyright (c) 2011 Matthew Francis
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package org.xbib.io.compress.bzip2;


/**
 * A 256 entry Move To Front transform
 */
public class MoveToFront {

    /**
     * The Move To Front list
     */
    private final byte[] mtf = {
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
            24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,
            46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
            68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89,
            90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108,
            109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125,
            126, 127, (byte) 128, (byte) 129, (byte) 130, (byte) 131, (byte) 132, (byte) 133, (byte) 134,
            (byte) 135, (byte) 136, (byte) 137, (byte) 138, (byte) 139, (byte) 140, (byte) 141, (byte) 142,
            (byte) 143, (byte) 144, (byte) 145, (byte) 146, (byte) 147, (byte) 148, (byte) 149, (byte) 150,
            (byte) 151, (byte) 152, (byte) 153, (byte) 154, (byte) 155, (byte) 156, (byte) 157, (byte) 158,
            (byte) 159, (byte) 160, (byte) 161, (byte) 162, (byte) 163, (byte) 164, (byte) 165, (byte) 166,
            (byte) 167, (byte) 168, (byte) 169, (byte) 170, (byte) 171, (byte) 172, (byte) 173, (byte) 174,
            (byte) 175, (byte) 176, (byte) 177, (byte) 178, (byte) 179, (byte) 180, (byte) 181, (byte) 182,
            (byte) 183, (byte) 184, (byte) 185, (byte) 186, (byte) 187, (byte) 188, (byte) 189, (byte) 190,
            (byte) 191, (byte) 192, (byte) 193, (byte) 194, (byte) 195, (byte) 196, (byte) 197, (byte) 198,
            (byte) 199, (byte) 200, (byte) 201, (byte) 202, (byte) 203, (byte) 204, (byte) 205, (byte) 206,
            (byte) 207, (byte) 208, (byte) 209, (byte) 210, (byte) 211, (byte) 212, (byte) 213, (byte) 214,
            (byte) 215, (byte) 216, (byte) 217, (byte) 218, (byte) 219, (byte) 220, (byte) 221, (byte) 222,
            (byte) 223, (byte) 224, (byte) 225, (byte) 226, (byte) 227, (byte) 228, (byte) 229, (byte) 230,
            (byte) 231, (byte) 232, (byte) 233, (byte) 234, (byte) 235, (byte) 236, (byte) 237, (byte) 238,
            (byte) 239, (byte) 240, (byte) 241, (byte) 242, (byte) 243, (byte) 244, (byte) 245, (byte) 246,
            (byte) 247, (byte) 248, (byte) 249, (byte) 250, (byte) 251, (byte) 252, (byte) 253, (byte) 254,
            (byte) 255
    };


    /**
     * Moves a value to the head of the MTF list (forward Move To Front transform)
     *
     * @param value The value to move
     * @return The position the value moved from
     */
    public int valueToFront(final byte value) {

        final byte[] mtf = this.mtf;

        int index = 0;
        byte temp = mtf[0];
        if (value != temp) {
            mtf[0] = value;
            while (value != temp) {
                index++;
                final byte temp2 = temp;
                temp = mtf[index];
                mtf[index] = temp2;
            }
        }

        return index;

    }


    /**
     * Gets the value from a given index and moves it to the front of the MTF list (inverse Move To
     * Front transform)
     *
     * @param index The index to move
     * @return The value at the given index
     */
    public byte indexToFront(final int index) {

        final byte[] mtf = this.mtf;

        final byte value = mtf[index];
        System.arraycopy(mtf, 0, mtf, 1, index);
        mtf[0] = value;

        return value;

    }

}