    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.EOFException;
    020import java.io.IOException;
    021import java.io.InputStream;
    022import java.util.ArrayList;
    023import java.util.Arrays;
    024import java.util.List;
    025
    026import org.apache.commons.compress.utils.ExactMath;
    027
    028/**
    029 * A BHSD codec is a means of encoding integer values as a sequence of bytes or vice versa using a specified "BHSD"
    030 * encoding mechanism. It uses a variable-length encoding and a modified sign representation such that small numbers are
    031 * represented as a single byte, whilst larger numbers take more bytes to encode. The number may be signed or unsigned;
    032 * if it is unsigned, it can be weighted towards positive numbers or equally distributed using a one's complement. The
    033 * Codec also supports delta coding, where a sequence of numbers is represented as a series of first-order differences.
    034 * So a delta encoding of the integers [1..10] would be represented as a sequence of 10x1s. This allows the absolute
    035 * value of a coded integer to fall outside of the 'small number' range, whilst still being encoded as a single byte.
    036 *
    037 * A BHSD codec is configured with four parameters:
    038 * <dl>
    039 * <dt>B</dt>
    040 * <dd>The maximum number of bytes that each value is encoded as. B must be a value between [1..5]. For a pass-through
    041 * coding (where each byte is encoded as itself, aka {@link #BYTE1}, B is 1 (each byte takes a maximum of 1 byte).</dd>
    042 * <dt>H</dt>
    043 * <dd>The radix of the integer. Values are defined as a sequence of values, where value {@code n} is multiplied by
    044 * {@code H^<sup>n</sup>}. So the number 1234 may be represented as the sequence 4 3 2 1 with a radix (H) of 10.
    045 * Note that other permutations are also possible; 43 2 1 will also encode 1234. The co-parameter L is defined as 256-H.
    046 * This is important because only the last value in a sequence may be &lt; L; all prior values must be &gt; L.</dd>
    047 * <dt>S</dt>
    048 * <dd>Whether the codec represents signed values (or not). This may have 3 values; 0 (unsigned), 1 (signed, one's
    049 * complement) or 2 (signed, two's complement)</dd>
    050 * <dt>D</dt>
    051 * <dd>Whether the codec represents a delta encoding. This may be 0 (no delta) or 1 (delta encoding). A delta encoding
    052 * of 1 indicates that values are cumulative; a sequence of {@code 1 1 1 1 1} will represent the sequence
    053 * {@code 1 2 3 4 5}. For this reason, the codec supports two variants of decode; one
    054 * {@link #decode(InputStream, long) with} and one {@link #decode(InputStream) without} a {@code last} parameter.
    055 * If the codec is a non-delta encoding, then the value is ignored if passed. If the codec is a delta encoding, it is a
    056 * run-time error to call the value without the extra parameter, and the previous value should be returned. (It was
    057 * designed this way to support multi-threaded access without requiring a new instance of the Codec to be cloned for
    058 * each use.)
    059 * </dd>
    060 * </dl>
    061 *
    062 * Codecs are notated as (B,H,S,D) and either D or S,D may be omitted if zero. Thus {@link #BYTE1} is denoted
    063 * (1,256,0,0) or (1,256). The {@link #toString()} method prints out the condensed form of the encoding. Often, the last
    064 * character in the name ({@link #BYTE1}, {@link #UNSIGNED5}) gives a clue as to the B value. Those that start with U
    065 * ({@link #UDELTA5}, {@link #UNSIGNED5}) are unsigned; otherwise, in most cases, they are signed. The presence of the
    066 * word Delta ({@link #DELTA5}, {@link #UDELTA5}) indicates a delta encoding is used.
    067 */
    068public final class BHSDCodec extends Codec {
    069
    070    /**
    071     * The maximum number of bytes in each coding word
    072     */
    073    private final int b;
    074
    075    /**
    076     * Whether delta encoding is used (0=false,1=true)
    077     */
    078    private final int d;
    079
    080    /**
    081     * The radix of the encoding
    082     */
    083    private final int h;
    084
    085    /**
    086     * The co-parameter of h; 256-h
    087     */
    088    private final int l;
    089
    090    /**
    091     * Represents signed numbers or not (0=unsigned,1/2=signed)
    092     */
    093    private final int s;
    094
    095    private long cardinality;
    096
    097    private final long smallest;
    098
    099    private final long largest;
    100
    101    /**
    102     * radix^i powers
    103     */
    104    private final long[] powers;
    105
    106    /**
    107     * Constructs an unsigned, non-delta Codec with the given B and H values.
    108     *
    109     * @param b the maximum number of bytes that a value can be encoded as [1..5]
    110     * @param h the radix of the encoding [1..256]
    111     */
    112    public BHSDCodec(final int b, final int h) {
    113        this(b, h, 0, 0);
    114    }
    115
    116    /**
    117     * Constructs a non-delta Codec with the given B, H and S values.
    118     *
    119     * @param b the maximum number of bytes that a value can be encoded as [1..5]
    120     * @param h the radix of the encoding [1..256]
    121     * @param s whether the encoding represents signed numbers (s=0 is unsigned; s=1 is signed with 1s complement; s=2
    122     *        is signed with ?)
    123     */
    124    public BHSDCodec(final int b, final int h, final int s) {
    125        this(b, h, s, 0);
    126    }
    127
    128    /**
    129     * Constructs a Codec with the given B, H, S and D values.
    130     *
    131     * @param b the maximum number of bytes that a value can be encoded as [1..5]
    132     * @param h the radix of the encoding [1..256]
    133     * @param s whether the encoding represents signed numbers (s=0 is unsigned; s=1 is signed with 1s complement; s=2
    134     *        is signed with ?)
    135     * @param d whether this is a delta encoding (d=0 is non-delta; d=1 is delta)
    136     */
    137    public BHSDCodec(final int b, final int h, final int s, final int d) {
    138        if (b < 1 || b > 5) {
    139            throw new IllegalArgumentException("1<=b<=5");
    140        }
    141        if (h < 1 || h > 256) {
    142            throw new IllegalArgumentException("1<=h<=256");
    143        }
    144        if (s < 0 || s > 2) {
    145            throw new IllegalArgumentException("0<=s<=2");
    146        }
    147        if (d < 0 || d > 1) {
    148            throw new IllegalArgumentException("0<=d<=1");
    149        }
    150        if (b == 1 && h != 256) {
    151            throw new IllegalArgumentException("b=1 -> h=256");
    152        }
    153        if (h == 256 && b == 5) {
    154            throw new IllegalArgumentException("h=256 -> b!=5");
    155        }
    156        this.b = b;
    157        this.h = h;
    158        this.s = s;
    159        this.d = d;
    160        this.l = 256 - h;
    161        if (h == 1) {
    162            cardinality = b * 255 + 1;
    163        } else {
    164            cardinality = (long) ((long) (l * (1 - Math.pow(h, b)) / (1 - h)) + Math.pow(h, b));
    165        }
    166        smallest = calculateSmallest();
    167        largest = calculateLargest();
    168
    169        powers = new long[b];
    170        Arrays.setAll(powers, c -> (long) Math.pow(h, c));
    171    }
    172
    173    private long calculateLargest() {
    174        long result;
    175        // TODO This can probably be optimized into a better mathematical
    176        // statement
    177        if (d == 1) {
    178            final BHSDCodec bh0 = new BHSDCodec(b, h);
    179            return bh0.largest();
    180        }
    181        switch (s) {
    182        case 0:
    183            result = cardinality() - 1;
    184            break;
    185        case 1:
    186            result = cardinality() / 2 - 1;
    187            break;
    188        case 2:
    189            result = (3L * cardinality()) / 4 - 1;
    190            break;
    191        default:
    192            throw new Error("Unknown s value");
    193        }
    194        return Math.min((s == 0 ? ((long) Integer.MAX_VALUE) << 1 : Integer.MAX_VALUE) - 1, result);
    195    }
    196
    197    private long calculateSmallest() {
    198        long result;
    199        if (d == 1 || !isSigned()) {
    200            if (cardinality >= 4294967296L) { // 2^32
    201                result = Integer.MIN_VALUE;
    202            } else {
    203                result = 0;
    204            }
    205        } else {
    206            result = Math.max(Integer.MIN_VALUE, -cardinality() / (1 << s));
    207        }
    208        return result;
    209    }
    210
    211    /**
    212     * Returns the cardinality of this codec; that is, the number of distinct values that it can contain.
    213     *
    214     * @return the cardinality of this codec
    215     */
    216    public long cardinality() {
    217        return cardinality;
    218    }
    219
    220    @Override
    221    public int decode(final InputStream in) throws IOException, Pack200Exception {
    222        if (d != 0) {
    223            throw new Pack200Exception("Delta encoding used without passing in last value; this is a coding error");
    224        }
    225        return decode(in, 0);
    226    }
    227
    228    @Override
    229    public int decode(final InputStream in, final long last) throws IOException, Pack200Exception {
    230        int n = 0;
    231        long z = 0;
    232        long x = 0;
    233
    234        do {
    235            x = in.read();
    236            lastBandLength++;
    237            z += x * powers[n];
    238            n++;
    239        } while (x >= l && n < b);
    240
    241        if (x == -1) {
    242            throw new EOFException("End of stream reached whilst decoding");
    243        }
    244
    245        if (isSigned()) {
    246            final int u = ((1 << s) - 1);
    247            if ((z & u) == u) {
    248                z = z >>> s ^ -1L;
    249            } else {
    250                z = z - (z >>> s);
    251            }
    252        }
    253        // This algorithm does the same thing, but is probably slower. Leaving
    254        // in for now for readability
    255        // if (isSigned()) {
    256        // long u = z;
    257        // long twoPowS = (long)Math.pow(2, s);
    258        // double twoPowSMinusOne = twoPowS-1;
    259        // if (u % twoPowS < twoPowSMinusOne) {
    260        // if (cardinality < Math.pow(2, 32)) {
    261        // z = (long) (u - (Math.floor(u/ twoPowS)));
    262        // } else {
    263        // z = cast32((long) (u - (Math.floor(u/ twoPowS))));
    264        // }
    265        // } else {
    266        // z = (long) (-Math.floor(u/ twoPowS) - 1);
    267        // }
    268        // }
    269        if (isDelta()) {
    270            z += last;
    271        }
    272        return (int) z;
    273    }
    274
    275    // private long cast32(long u) {
    276    // u = (long) ((long) ((u + Math.pow(2, 31)) % Math.pow(2, 32)) -
    277    // Math.pow(2, 31));
    278    // return u;
    279    // }
    280
    281    @Override
    282    public int[] decodeInts(final int n, final InputStream in) throws IOException, Pack200Exception {
    283        final int[] band = super.decodeInts(n, in);
    284        if (isDelta()) {
    285            for (int i = 0; i < band.length; i++) {
    286                while (band[i] > largest) {
    287                    band[i] -= cardinality;
    288                }
    289                while (band[i] < smallest) {
    290                    band[i] = ExactMath.add(band[i], cardinality);
    291                }
    292            }
    293        }
    294        return band;
    295    }
    296
    297    @Override
    298    public int[] decodeInts(final int n, final InputStream in, final int firstValue)
    299        throws IOException, Pack200Exception {
    300        final int[] band = super.decodeInts(n, in, firstValue);
    301        if (isDelta()) {
    302            for (int i = 0; i < band.length; i++) {
    303                while (band[i] > largest) {
    304                    band[i] -= cardinality;
    305                }
    306                while (band[i] < smallest) {
    307                    band[i] = ExactMath.add(band[i], cardinality);
    308                }
    309            }
    310        }
    311        return band;
    312    }
    313
    314    @Override
    315    public byte[] encode(final int value) throws Pack200Exception {
    316        return encode(value, 0);
    317    }
    318
    319    @Override
    320    public byte[] encode(final int value, final int last) throws Pack200Exception {
    321        if (!encodes(value)) {
    322            throw new Pack200Exception("The codec " + this + " does not encode the value " + value);
    323        }
    324
    325        long z = value;
    326        if (isDelta()) {
    327            z -= last;
    328        }
    329        if (isSigned()) {
    330            if (z < Integer.MIN_VALUE) {
    331                z += 4294967296L;
    332            } else if (z > Integer.MAX_VALUE) {
    333                z -= 4294967296L;
    334            }
    335            if (z < 0) {
    336                z = (-z << s) - 1;
    337            } else if (s == 1) {
    338                z = z << s;
    339            } else {
    340                z += (z - z % 3) / 3;
    341            }
    342        } else if (z < 0) {
    343            // Need to use integer overflow here to represent negatives.
    344            // 4294967296L is the 1 << 32.
    345            z += Math.min(cardinality, 4294967296L);
    346        }
    347        if (z < 0) {
    348            throw new Pack200Exception("unable to encode");
    349        }
    350
    351        final List<Byte> byteList = new ArrayList<>();
    352        for (int n = 0; n < b; n++) {
    353            long byteN;
    354            if (z < l) {
    355                byteN = z;
    356            } else {
    357                byteN = z % h;
    358                while (byteN < l) {
    359                    byteN += h;
    360                }
    361            }
    362            byteList.add(Byte.valueOf((byte) byteN));
    363            if (byteN < l) {
    364                break;
    365            }
    366            z -= byteN;
    367            z /= h;
    368        }
    369        final byte[] bytes = new byte[byteList.size()];
    370        for (int i = 0; i < bytes.length; i++) {
    371            bytes[i] = byteList.get(i).byteValue();
    372        }
    373        return bytes;
    374    }
    375
    376    /**
    377     * True if this encoding can code the given value
    378     *
    379     * @param value the value to check
    380     * @return {@code true} if the encoding can encode this value
    381     */
    382    public boolean encodes(final long value) {
    383        return value >= smallest && value <= largest;
    384    }
    385
    386    @Override
    387    public boolean equals(final Object o) {
    388        if (o instanceof BHSDCodec) {
    389            final BHSDCodec codec = (BHSDCodec) o;
    390            return codec.b == b && codec.h == h && codec.s == s && codec.d == d;
    391        }
    392        return false;
    393    }
    394
    395    /**
    396     * @return the b
    397     */
    398    public int getB() {
    399        return b;
    400    }
    401
    402    /**
    403     * @return the h
    404     */
    405    public int getH() {
    406        return h;
    407    }
    408
    409    /**
    410     * @return the l
    411     */
    412    public int getL() {
    413        return l;
    414    }
    415
    416    /**
    417     * @return the s
    418     */
    419    public int getS() {
    420        return s;
    421    }
    422
    423    @Override
    424    public int hashCode() {
    425        return ((b * 37 + h) * 37 + s) * 37 + d;
    426    }
    427
    428    /**
    429     * Returns true if this codec is a delta codec
    430     *
    431     * @return true if this codec is a delta codec
    432     */
    433    public boolean isDelta() {
    434        return d != 0;
    435    }
    436
    437    /**
    438     * Returns true if this codec is a signed codec
    439     *
    440     * @return true if this codec is a signed codec
    441     */
    442    public boolean isSigned() {
    443        return s != 0;
    444    }
    445
    446    /**
    447     * Returns the largest value that this codec can represent.
    448     *
    449     * @return the largest value that this codec can represent.
    450     */
    451    public long largest() {
    452        return largest;
    453    }
    454
    455    /**
    456     * Returns the smallest value that this codec can represent.
    457     *
    458     * @return the smallest value that this codec can represent.
    459     */
    460    public long smallest() {
    461        return smallest;
    462    }
    463
    464    /**
    465     * Returns the codec in the form (1,256) or (1,64,1,1). Note that trailing zero fields are not shown.
    466     */
    467    @Override
    468    public String toString() {
    469        final StringBuilder buffer = new StringBuilder(11);
    470        buffer.append('(');
    471        buffer.append(b);
    472        buffer.append(',');
    473        buffer.append(h);
    474        if (s != 0 || d != 0) {
    475            buffer.append(',');
    476            buffer.append(s);
    477        }
    478        if (d != 0) {
    479            buffer.append(',');
    480            buffer.append(d);
    481        }
    482        buffer.append(')');
    483        return buffer.toString();
    484    }
    485}