    001/*
    002 *  Licensed to the Apache Software Foundation (ASF) under one or more
    003 *  contributor license agreements.  See the NOTICE file distributed with
    004 *  this work for additional information regarding copyright ownership.
    005 *  The ASF licenses this file to You under the Apache License, Version 2.0
    006 *  (the "License"); you may not use this file except in compliance with
    007 *  the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 */
    017package org.apache.commons.compress.harmony.pack200;
    018
    019import java.io.IOException;
    020import java.io.InputStream;
    021import java.util.Arrays;
    022
    023/**
    024 * A PopulationCodec is a Codec that is well suited to encoding data that shows statistical or repetitive patterns,
    025 * containing for example a few numbers which are repeated a lot throughout the set, but not necessarily sequentially.
    026 */
    027public class PopulationCodec extends Codec {
    028
    029    private final Codec favouredCodec;
    030    private Codec tokenCodec;
    031    private final Codec unfavouredCodec;
    032    private int l;
    033    private int[] favoured;
    034
    035    public PopulationCodec(final Codec favouredCodec, final Codec tokenCodec, final Codec unvafouredCodec) {
    036        this.favouredCodec = favouredCodec;
    037        this.tokenCodec = tokenCodec;
    038        this.unfavouredCodec = unvafouredCodec;
    039    }
    040
    041    public PopulationCodec(final Codec favouredCodec, final int l, final Codec unfavouredCodec) {
    042        if (l >= 256 || l <= 0) {
    043            throw new IllegalArgumentException("L must be between 1..255");
    044        }
    045        this.favouredCodec = favouredCodec;
    046        this.l = l;
    047        this.unfavouredCodec = unfavouredCodec;
    048    }
    049
    050    @Override
    051    public int decode(final InputStream in) throws IOException, Pack200Exception {
    052        throw new Pack200Exception("Population encoding does not work unless the number of elements are known");
    053    }
    054
    055    @Override
    056    public int decode(final InputStream in, final long last) throws IOException, Pack200Exception {
    057        throw new Pack200Exception("Population encoding does not work unless the number of elements are known");
    058    }
    059
    060    @Override
    061    public int[] decodeInts(final int n, final InputStream in) throws IOException, Pack200Exception {
    062        lastBandLength = 0;
    063        favoured = new int[n]; // there must be <= n values, but probably a lot
    064        // less
    065        int[] result;
    066        // read table of favorites first
    067        int smallest = Integer.MAX_VALUE, absoluteSmallest;
    068        int last = 0;
    069        int value = 0, absoluteValue;
    070        int k = -1;
    071        while (true) {
    072            value = favouredCodec.decode(in, last);
    073            if (k > -1 && (value == smallest || value == last)) {
    074                break;
    075            }
    076            favoured[++k] = value;
    077            absoluteSmallest = Math.abs(smallest);
    078            absoluteValue = Math.abs(value);
    079            if (absoluteSmallest > absoluteValue) {
    080                smallest = value;
    081            } else if (absoluteSmallest == absoluteValue) {
    082                // ensure that -X and +X -> +X
    083                smallest = absoluteSmallest;
    084            }
    085            last = value;
    086        }
    087        lastBandLength += k;
    088        // if tokenCodec needs to be derived from the T, L and K values
    089        if (tokenCodec == null) {
    090            if (k < 256) {
    091                tokenCodec = Codec.BYTE1;
    092            } else {
    093                // if k >= 256, b >= 2
    094                int b = 1;
    095                BHSDCodec codec = null;
    096                while (++b < 5) {
    097                    codec = new BHSDCodec(b, 256 - l, 0);
    098                    if (codec.encodes(k)) {
    099                        tokenCodec = codec;
    100                        break;
    101                    }
    102                }
    103                if (tokenCodec == null) {
    104                    throw new Pack200Exception("Cannot calculate token codec from " + k + " and " + l);
    105                }
    106            }
    107        }
    108        // read favorites
    109        lastBandLength += n;
    110        result = tokenCodec.decodeInts(n, in);
    111        // read unfavorites
    112        last = 0;
    113        for (int i = 0; i < n; i++) {
    114            final int index = result[i];
    115            if (index == 0) {
    116                lastBandLength++;
    117                result[i] = last = unfavouredCodec.decode(in, last);
    118            } else {
    119                result[i] = favoured[index - 1];
    120            }
    121        }
    122        return result;
    123    }
    124
    125    @Override
    126    public byte[] encode(final int value) throws Pack200Exception {
    127        throw new Pack200Exception("Population encoding does not work unless the number of elements are known");
    128    }
    129
    130    @Override
    131    public byte[] encode(final int value, final int last) throws Pack200Exception {
    132        throw new Pack200Exception("Population encoding does not work unless the number of elements are known");
    133    }
    134
    135    public byte[] encode(final int[] favoured, final int[] tokens, final int[] unfavoured) throws Pack200Exception {
    136        final int[] favoured2 = Arrays.copyOf(favoured, favoured.length + 1);
    137        favoured2[favoured2.length - 1] = favoured[favoured.length - 1]; // repeat last value;
    138        final byte[] favouredEncoded = favouredCodec.encode(favoured2);
    139        final byte[] tokensEncoded = tokenCodec.encode(tokens);
    140        final byte[] unfavouredEncoded = unfavouredCodec.encode(unfavoured);
    141        final byte[] band = new byte[favouredEncoded.length + tokensEncoded.length + unfavouredEncoded.length];
    142        System.arraycopy(favouredEncoded, 0, band, 0, favouredEncoded.length);
    143        System.arraycopy(tokensEncoded, 0, band, favouredEncoded.length, tokensEncoded.length);
    144        System.arraycopy(unfavouredEncoded, 0, band, favouredEncoded.length + tokensEncoded.length,
    145            unfavouredEncoded.length);
    146        return band;
    147    }
    148
    149    public int[] getFavoured() {
    150        return favoured;
    151    }
    152
    153    public Codec getFavouredCodec() {
    154        return favouredCodec;
    155    }
    156
    157    public Codec getTokenCodec() {
    158        return tokenCodec;
    159    }
    160
    161    public Codec getUnfavouredCodec() {
    162        return unfavouredCodec;
    163    }
    164}