    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one
    003     * or more contributor license agreements.  See the NOTICE file
    004     * distributed with this work for additional information
    005     * regarding copyright ownership.  The ASF licenses this file
    006     * to you under the Apache License, Version 2.0 (the
    007     * "License"); you may not use this file except in compliance
    008     * with the License.  You may obtain a copy of the License at
    009     *
    010     * http://www.apache.org/licenses/LICENSE-2.0
    011     *
    012     * Unless required by applicable law or agreed to in writing,
    013     * software distributed under the License is distributed on an
    014     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    015     * KIND, either express or implied.  See the License for the
    016     * specific language governing permissions and limitations
    017     * under the License.
    018     */
    019
    020    /*
    021     * This package is based on the work done by Keiron Liddle, Aftex Software
    022     * <keiron@aftexsw.com> to whom the Ant project is very grateful for his
    023     * great code.
    024     */
    025    package org.apache.commons.compress.compressors.bzip2;
    026
    027    import java.io.IOException;
    028    import java.io.InputStream;
    029
    030    import org.apache.commons.compress.compressors.CompressorInputStream;
    031
    032    /**
    033     * An input stream that decompresses from the BZip2 format to be read as any other stream.
    034     *
    035     * @NotThreadSafe
    036     */
    037    public class BZip2CompressorInputStream extends CompressorInputStream implements
    038                                                                              BZip2Constants {
    039
    040        /**
    041         * Index of the last char in the block, so the block size == last + 1.
    042         */
    043        private int last;
    044
    045        /**
    046         * Index in zptr[] of original string after sorting.
    047         */
    048        private int origPtr;
    049
    050        /**
    051         * always: in the range 0 .. 9. The current block size is 100000 * this
    052         * number.
    053         */
    054        private int blockSize100k;
    055
    056        private boolean blockRandomised;
    057
    058        private int bsBuff;
    059        private int bsLive;
    060        private final CRC crc = new CRC();
    061
    062        private int nInUse;
    063
    064        private InputStream in;
    065
    066        private int currentChar = -1;
    067
    068        private static final int EOF = 0;
    069        private static final int START_BLOCK_STATE = 1;
    070        private static final int RAND_PART_A_STATE = 2;
    071        private static final int RAND_PART_B_STATE = 3;
    072        private static final int RAND_PART_C_STATE = 4;
    073        private static final int NO_RAND_PART_A_STATE = 5;
    074        private static final int NO_RAND_PART_B_STATE = 6;
    075        private static final int NO_RAND_PART_C_STATE = 7;
    076
    077        private int currentState = START_BLOCK_STATE;
    078
    079        private int storedBlockCRC, storedCombinedCRC;
    080        private int computedBlockCRC, computedCombinedCRC;
    081
    082        // Variables used by setup* methods exclusively
    083
    084        private int su_count;
    085        private int su_ch2;
    086        private int su_chPrev;
    087        private int su_i2;
    088        private int su_j2;
    089        private int su_rNToGo;
    090        private int su_rTPos;
    091        private int su_tPos;
    092        private char su_z;
    093
    094        /**
    095         * All memory intensive stuff. This field is initialized by initBlock().
    096         */
    097        private BZip2CompressorInputStream.Data data;
    098
    099        /**
    100         * Constructs a new BZip2CompressorInputStream which decompresses bytes read from the
    101         * specified stream.
    102         *
    103         * @throws IOException
    104         *             if the stream content is malformed or an I/O error occurs.
    105         * @throws NullPointerException
    106         *             if <tt>in == null</tt>
    107         */
    108        public BZip2CompressorInputStream(final InputStream in) throws IOException {
    109            super();
    110
    111            this.in = in;
    112            init();
    113        }
    114
    115        /** {@inheritDoc} */
    116        public int read() throws IOException {
    117            if (this.in != null) {
    118                return read0();
    119            } else {
    120                throw new IOException("stream closed");
    121            }
    122        }
    123
    124        /*
    125         * (non-Javadoc)
    126         *
    127         * @see java.io.InputStream#read(byte[], int, int)
    128         */
    129        public int read(final byte[] dest, final int offs, final int len)
    130            throws IOException {
    131            if (offs < 0) {
    132                throw new IndexOutOfBoundsException("offs(" + offs + ") < 0.");
    133            }
    134            if (len < 0) {
    135                throw new IndexOutOfBoundsException("len(" + len + ") < 0.");
    136            }
    137            if (offs + len > dest.length) {
    138                throw new IndexOutOfBoundsException("offs(" + offs + ") + len("
    139                                                    + len + ") > dest.length(" + dest.length + ").");
    140            }
    141            if (this.in == null) {
    142                throw new IOException("stream closed");
    143            }
    144
    145            final int hi = offs + len;
    146            int destOffs = offs;
    147            for (int b; (destOffs < hi) && ((b = read0()) >= 0);) {
    148                dest[destOffs++] = (byte) b;
    149            }
    150
    151            return (destOffs == offs) ? -1 : (destOffs - offs);
    152        }
    153
    154        private void makeMaps() {
    155            final boolean[] inUse = this.data.inUse;
    156            final byte[] seqToUnseq = this.data.seqToUnseq;
    157
    158            int nInUseShadow = 0;
    159
    160            for (int i = 0; i < 256; i++) {
    161                if (inUse[i])
    162                    seqToUnseq[nInUseShadow++] = (byte) i;
    163            }
    164
    165            this.nInUse = nInUseShadow;
    166        }
    167
    168        private int read0() throws IOException {
    169            final int retChar = this.currentChar;
    170
    171            switch (this.currentState) {
    172            case EOF:
    173                return -1;
    174
    175            case START_BLOCK_STATE:
    176                throw new IllegalStateException();
    177
    178            case RAND_PART_A_STATE:
    179                throw new IllegalStateException();
    180
    181            case RAND_PART_B_STATE:
    182                setupRandPartB();
    183                break;
    184
    185            case RAND_PART_C_STATE:
    186                setupRandPartC();
    187                break;
    188
    189            case NO_RAND_PART_A_STATE:
    190                throw new IllegalStateException();
    191
    192            case NO_RAND_PART_B_STATE:
    193                setupNoRandPartB();
    194                break;
    195
    196            case NO_RAND_PART_C_STATE:
    197                setupNoRandPartC();
    198                break;
    199
    200            default:
    201                throw new IllegalStateException();
    202            }
    203
    204            return retChar;
    205        }
    206
    207        private void init() throws IOException {
    208            if (null == in) {
    209                throw new IOException("No InputStream");
    210            }
    211            if (in.available() == 0) {
    212                throw new IOException("Empty InputStream");
    213            }
    214            checkMagicChar('B', "first");
    215            checkMagicChar('Z', "second");
    216            checkMagicChar('h', "third");
    217
    218            int blockSize = this.in.read();
    219            if ((blockSize < '1') || (blockSize > '9')) {
    220                throw new IOException("Stream is not BZip2 formatted: illegal "
    221                                      + "blocksize " + (char) blockSize);
    222            }
    223
    224            this.blockSize100k = blockSize - '0';
    225
    226            initBlock();
    227            setupBlock();
    228        }
    229
    230        private void checkMagicChar(char expected, String position)
    231            throws IOException {
    232            int magic = this.in.read();
    233            if (magic != expected) {
    234                throw new IOException("Stream is not BZip2 formatted: expected '"
    235                                      + expected + "' as " + position + " byte but got '"
    236                                      + (char) magic + "'");
    237            }
    238        }
    239
    240        private void initBlock() throws IOException {
    241            char magic0 = bsGetUByte();
    242            char magic1 = bsGetUByte();
    243            char magic2 = bsGetUByte();
    244            char magic3 = bsGetUByte();
    245            char magic4 = bsGetUByte();
    246            char magic5 = bsGetUByte();
    247
    248            if (magic0 == 0x17 && magic1 == 0x72 && magic2 == 0x45
    249                && magic3 == 0x38 && magic4 == 0x50 && magic5 == 0x90) {
    250                complete(); // end of file
    251            } else if (magic0 != 0x31 || // '1'
    252                       magic1 != 0x41 || // ')'
    253                       magic2 != 0x59 || // 'Y'
    254                       magic3 != 0x26 || // '&'
    255                       magic4 != 0x53 || // 'S'
    256                       magic5 != 0x59 // 'Y'
    257                       ) {
    258                this.currentState = EOF;
    259                throw new IOException("bad block header");
    260            } else {
    261                this.storedBlockCRC = bsGetInt();
    262                this.blockRandomised = bsR(1) == 1;
    263
    264                /**
    265                 * Allocate data here instead in constructor, so we do not allocate
    266                 * it if the input file is empty.
    267                 */
    268                if (this.data == null) {
    269                    this.data = new Data(this.blockSize100k);
    270                }
    271
    272                // currBlockNo++;
    273                getAndMoveToFrontDecode();
    274
    275                this.crc.initialiseCRC();
    276                this.currentState = START_BLOCK_STATE;
    277            }
    278        }
    279
    280        private void endBlock() throws IOException {
    281            this.computedBlockCRC = this.crc.getFinalCRC();
    282
    283            // A bad CRC is considered a fatal error.
    284            if (this.storedBlockCRC != this.computedBlockCRC) {
    285                // make next blocks readable without error
    286                // (repair feature, not yet documented, not tested)
    287                this.computedCombinedCRC = (this.storedCombinedCRC << 1)
    288                    | (this.storedCombinedCRC >>> 31);
    289                this.computedCombinedCRC ^= this.storedBlockCRC;
    290
    291                throw new IOException("BZip2 CRC error");
    292            }
    293
    294            this.computedCombinedCRC = (this.computedCombinedCRC << 1)
    295                | (this.computedCombinedCRC >>> 31);
    296            this.computedCombinedCRC ^= this.computedBlockCRC;
    297        }
    298
    299        private void complete() throws IOException {
    300            this.storedCombinedCRC = bsGetInt();
    301            this.currentState = EOF;
    302            this.data = null;
    303
    304            if (this.storedCombinedCRC != this.computedCombinedCRC) {
    305                throw new IOException("BZip2 CRC error");
    306            }
    307        }
    308
    309        public void close() throws IOException {
    310            InputStream inShadow = this.in;
    311            if (inShadow != null) {
    312                try {
    313                    if (inShadow != System.in) {
    314                        inShadow.close();
    315                    }
    316                } finally {
    317                    this.data = null;
    318                    this.in = null;
    319                }
    320            }
    321        }
    322
    323        private int bsR(final int n) throws IOException {
    324            int bsLiveShadow = this.bsLive;
    325            int bsBuffShadow = this.bsBuff;
    326
    327            if (bsLiveShadow < n) {
    328                final InputStream inShadow = this.in;
    329                do {
    330                    int thech = inShadow.read();
    331
    332                    if (thech < 0) {
    333                        throw new IOException("unexpected end of stream");
    334                    }
    335
    336                    bsBuffShadow = (bsBuffShadow << 8) | thech;
    337                    bsLiveShadow += 8;
    338                } while (bsLiveShadow < n);
    339
    340                this.bsBuff = bsBuffShadow;
    341            }
    342
    343            this.bsLive = bsLiveShadow - n;
    344            return (bsBuffShadow >> (bsLiveShadow - n)) & ((1 << n) - 1);
    345        }
    346
    347        private boolean bsGetBit() throws IOException {
    348            int bsLiveShadow = this.bsLive;
    349            int bsBuffShadow = this.bsBuff;
    350
    351            if (bsLiveShadow < 1) {
    352                int thech = this.in.read();
    353
    354                if (thech < 0) {
    355                    throw new IOException("unexpected end of stream");
    356                }
    357
    358                bsBuffShadow = (bsBuffShadow << 8) | thech;
    359                bsLiveShadow += 8;
    360                this.bsBuff = bsBuffShadow;
    361            }
    362
    363            this.bsLive = bsLiveShadow - 1;
    364            return ((bsBuffShadow >> (bsLiveShadow - 1)) & 1) != 0;
    365        }
    366
    367        private char bsGetUByte() throws IOException {
    368            return (char) bsR(8);
    369        }
    370
    371        private int bsGetInt() throws IOException {
    372            return (((((bsR(8) << 8) | bsR(8)) << 8) | bsR(8)) << 8) | bsR(8);
    373        }
    374
    375        /**
    376         * Called by createHuffmanDecodingTables() exclusively.
    377         */
    378        private static void hbCreateDecodeTables(final int[] limit,
    379                                                 final int[] base, final int[] perm, final char[] length,
    380                                                 final int minLen, final int maxLen, final int alphaSize) {
    381            for (int i = minLen, pp = 0; i <= maxLen; i++) {
    382                for (int j = 0; j < alphaSize; j++) {
    383                    if (length[j] == i) {
    384                        perm[pp++] = j;
    385                    }
    386                }
    387            }
    388
    389            for (int i = MAX_CODE_LEN; --i > 0;) {
    390                base[i] = 0;
    391                limit[i] = 0;
    392            }
    393
    394            for (int i = 0; i < alphaSize; i++) {
    395                base[length[i] + 1]++;
    396            }
    397
    398            for (int i = 1, b = base[0]; i < MAX_CODE_LEN; i++) {
    399                b += base[i];
    400                base[i] = b;
    401            }
    402
    403            for (int i = minLen, vec = 0, b = base[i]; i <= maxLen; i++) {
    404                final int nb = base[i + 1];
    405                vec += nb - b;
    406                b = nb;
    407                limit[i] = vec - 1;
    408                vec <<= 1;
    409            }
    410
    411            for (int i = minLen + 1; i <= maxLen; i++) {
    412                base[i] = ((limit[i - 1] + 1) << 1) - base[i];
    413            }
    414        }
    415
    416        private void recvDecodingTables() throws IOException {
    417            final Data dataShadow = this.data;
    418            final boolean[] inUse = dataShadow.inUse;
    419            final byte[] pos = dataShadow.recvDecodingTables_pos;
    420            final byte[] selector = dataShadow.selector;
    421            final byte[] selectorMtf = dataShadow.selectorMtf;
    422
    423            int inUse16 = 0;
    424
    425            /* Receive the mapping table */
    426            for (int i = 0; i < 16; i++) {
    427                if (bsGetBit()) {
    428                    inUse16 |= 1 << i;
    429                }
    430            }
    431
    432            for (int i = 256; --i >= 0;) {
    433                inUse[i] = false;
    434            }
    435
    436            for (int i = 0; i < 16; i++) {
    437                if ((inUse16 & (1 << i)) != 0) {
    438                    final int i16 = i << 4;
    439                    for (int j = 0; j < 16; j++) {
    440                        if (bsGetBit()) {
    441                            inUse[i16 + j] = true;
    442                        }
    443                    }
    444                }
    445            }
    446
    447            makeMaps();
    448            final int alphaSize = this.nInUse + 2;
    449
    450            /* Now the selectors */
    451            final int nGroups = bsR(3);
    452            final int nSelectors = bsR(15);
    453
    454            for (int i = 0; i < nSelectors; i++) {
    455                int j = 0;
    456                while (bsGetBit()) {
    457                    j++;
    458                }
    459                selectorMtf[i] = (byte) j;
    460            }
    461
    462            /* Undo the MTF values for the selectors. */
    463            for (int v = nGroups; --v >= 0;) {
    464                pos[v] = (byte) v;
    465            }
    466
    467            for (int i = 0; i < nSelectors; i++) {
    468                int v = selectorMtf[i] & 0xff;
    469                final byte tmp = pos[v];
    470                while (v > 0) {
    471                    // nearly all times v is zero, 4 in most other cases
    472                    pos[v] = pos[v - 1];
    473                    v--;
    474                }
    475                pos[0] = tmp;
    476                selector[i] = tmp;
    477            }
    478
    479            final char[][] len = dataShadow.temp_charArray2d;
    480
    481            /* Now the coding tables */
    482            for (int t = 0; t < nGroups; t++) {
    483                int curr = bsR(5);
    484                final char[] len_t = len[t];
    485                for (int i = 0; i < alphaSize; i++) {
    486                    while (bsGetBit()) {
    487                        curr += bsGetBit() ? -1 : 1;
    488                    }
    489                    len_t[i] = (char) curr;
    490                }
    491            }
    492
    493            // finally create the Huffman tables
    494            createHuffmanDecodingTables(alphaSize, nGroups);
    495        }
    496
    497        /**
    498         * Called by recvDecodingTables() exclusively.
    499         */
    500        private void createHuffmanDecodingTables(final int alphaSize,
    501                                                 final int nGroups) {
    502            final Data dataShadow = this.data;
    503            final char[][] len = dataShadow.temp_charArray2d;
    504            final int[] minLens = dataShadow.minLens;
    505            final int[][] limit = dataShadow.limit;
    506            final int[][] base = dataShadow.base;
    507            final int[][] perm = dataShadow.perm;
    508
    509            for (int t = 0; t < nGroups; t++) {
    510                int minLen = 32;
    511                int maxLen = 0;
    512                final char[] len_t = len[t];
    513                for (int i = alphaSize; --i >= 0;) {
    514                    final char lent = len_t[i];
    515                    if (lent > maxLen) {
    516                        maxLen = lent;
    517                    }
    518                    if (lent < minLen) {
    519                        minLen = lent;
    520                    }
    521                }
    522                hbCreateDecodeTables(limit[t], base[t], perm[t], len[t], minLen,
    523                                     maxLen, alphaSize);
    524                minLens[t] = minLen;
    525            }
    526        }
    527
    528        private void getAndMoveToFrontDecode() throws IOException {
    529            this.origPtr = bsR(24);
    530            recvDecodingTables();
    531
    532            final InputStream inShadow = this.in;
    533            final Data dataShadow = this.data;
    534            final byte[] ll8 = dataShadow.ll8;
    535            final int[] unzftab = dataShadow.unzftab;
    536            final byte[] selector = dataShadow.selector;
    537            final byte[] seqToUnseq = dataShadow.seqToUnseq;
    538            final char[] yy = dataShadow.getAndMoveToFrontDecode_yy;
    539            final int[] minLens = dataShadow.minLens;
    540            final int[][] limit = dataShadow.limit;
    541            final int[][] base = dataShadow.base;
    542            final int[][] perm = dataShadow.perm;
    543            final int limitLast = this.blockSize100k * 100000;
    544
    545            /*
    546             * Setting up the unzftab entries here is not strictly necessary, but it
    547             * does save having to do it later in a separate pass, and so saves a
    548             * block's worth of cache misses.
    549             */
    550            for (int i = 256; --i >= 0;) {
    551                yy[i] = (char) i;
    552                unzftab[i] = 0;
    553            }
    554
    555            int groupNo = 0;
    556            int groupPos = G_SIZE - 1;
    557            final int eob = this.nInUse + 1;
    558            int nextSym = getAndMoveToFrontDecode0(0);
    559            int bsBuffShadow = this.bsBuff;
    560            int bsLiveShadow = this.bsLive;
    561            int lastShadow = -1;
    562            int zt = selector[groupNo] & 0xff;
    563            int[] base_zt = base[zt];
    564            int[] limit_zt = limit[zt];
    565            int[] perm_zt = perm[zt];
    566            int minLens_zt = minLens[zt];
    567
    568            while (nextSym != eob) {
    569                if ((nextSym == RUNA) || (nextSym == RUNB)) {
    570                    int s = -1;
    571
    572                    for (int n = 1; true; n <<= 1) {
    573                        if (nextSym == RUNA) {
    574                            s += n;
    575                        } else if (nextSym == RUNB) {
    576                            s += n << 1;
    577                        } else {
    578                            break;
    579                        }
    580
    581                        if (groupPos == 0) {
    582                            groupPos = G_SIZE - 1;
    583                            zt = selector[++groupNo] & 0xff;
    584                            base_zt = base[zt];
    585                            limit_zt = limit[zt];
    586                            perm_zt = perm[zt];
    587                            minLens_zt = minLens[zt];
    588                        } else {
    589                            groupPos--;
    590                        }
    591
    592                        int zn = minLens_zt;
    593
    594                        // Inlined:
    595                        // int zvec = bsR(zn);
    596                        while (bsLiveShadow < zn) {
    597                            final int thech = inShadow.read();
    598                            if (thech >= 0) {
    599                                bsBuffShadow = (bsBuffShadow << 8) | thech;
    600                                bsLiveShadow += 8;
    601                                continue;
    602                            } else {
    603                                throw new IOException("unexpected end of stream");
    604                            }
    605                        }
    606                        int zvec = (bsBuffShadow >> (bsLiveShadow - zn))
    607                            & ((1 << zn) - 1);
    608                        bsLiveShadow -= zn;
    609
    610                        while (zvec > limit_zt[zn]) {
    611                            zn++;
    612                            while (bsLiveShadow < 1) {
    613                                final int thech = inShadow.read();
    614                                if (thech >= 0) {
    615                                    bsBuffShadow = (bsBuffShadow << 8) | thech;
    616                                    bsLiveShadow += 8;
    617                                    continue;
    618                                } else {
    619                                    throw new IOException(
    620                                                          "unexpected end of stream");
    621                                }
    622                            }
    623                            bsLiveShadow--;
    624                            zvec = (zvec << 1)
    625                                | ((bsBuffShadow >> bsLiveShadow) & 1);
    626                        }
    627                        nextSym = perm_zt[zvec - base_zt[zn]];
    628                    }
    629
    630                    final byte ch = seqToUnseq[yy[0]];
    631                    unzftab[ch & 0xff] += s + 1;
    632
    633                    while (s-- >= 0) {
    634                        ll8[++lastShadow] = ch;
    635                    }
    636
    637                    if (lastShadow >= limitLast) {
    638                        throw new IOException("block overrun");
    639                    }
    640                } else {
    641                    if (++lastShadow >= limitLast) {
    642                        throw new IOException("block overrun");
    643                    }
    644
    645                    final char tmp = yy[nextSym - 1];
    646                    unzftab[seqToUnseq[tmp] & 0xff]++;
    647                    ll8[lastShadow] = seqToUnseq[tmp];
    648
    649                    /*
    650                     * This loop is hammered during decompression, hence avoid
    651                     * native method call overhead of System.arraycopy for very
    652                     * small ranges to copy.
    653                     */
    654                    if (nextSym <= 16) {
    655                        for (int j = nextSym - 1; j > 0;) {
    656                            yy[j] = yy[--j];
    657                        }
    658                    } else {
    659                        System.arraycopy(yy, 0, yy, 1, nextSym - 1);
    660                    }
    661
    662                    yy[0] = tmp;
    663
    664                    if (groupPos == 0) {
    665                        groupPos = G_SIZE - 1;
    666                        zt = selector[++groupNo] & 0xff;
    667                        base_zt = base[zt];
    668                        limit_zt = limit[zt];
    669                        perm_zt = perm[zt];
    670                        minLens_zt = minLens[zt];
    671                    } else {
    672                        groupPos--;
    673                    }
    674
    675                    int zn = minLens_zt;
    676
    677                    // Inlined:
    678                    // int zvec = bsR(zn);
    679                    while (bsLiveShadow < zn) {
    680                        final int thech = inShadow.read();
    681                        if (thech >= 0) {
    682                            bsBuffShadow = (bsBuffShadow << 8) | thech;
    683                            bsLiveShadow += 8;
    684                            continue;
    685                        } else {
    686                            throw new IOException("unexpected end of stream");
    687                        }
    688                    }
    689                    int zvec = (bsBuffShadow >> (bsLiveShadow - zn))
    690                        & ((1 << zn) - 1);
    691                    bsLiveShadow -= zn;
    692
    693                    while (zvec > limit_zt[zn]) {
    694                        zn++;
    695                        while (bsLiveShadow < 1) {
    696                            final int thech = inShadow.read();
    697                            if (thech >= 0) {
    698                                bsBuffShadow = (bsBuffShadow << 8) | thech;
    699                                bsLiveShadow += 8;
    700                                continue;
    701                            } else {
    702                                throw new IOException("unexpected end of stream");
    703                            }
    704                        }
    705                        bsLiveShadow--;
    706                        zvec = (zvec << 1) | ((bsBuffShadow >> bsLiveShadow) & 1);
    707                    }
    708                    nextSym = perm_zt[zvec - base_zt[zn]];
    709                }
    710            }
    711
    712            this.last = lastShadow;
    713            this.bsLive = bsLiveShadow;
    714            this.bsBuff = bsBuffShadow;
    715        }
    716
    717        private int getAndMoveToFrontDecode0(final int groupNo) throws IOException {
    718            final InputStream inShadow = this.in;
    719            final Data dataShadow = this.data;
    720            final int zt = dataShadow.selector[groupNo] & 0xff;
    721            final int[] limit_zt = dataShadow.limit[zt];
    722            int zn = dataShadow.minLens[zt];
    723            int zvec = bsR(zn);
    724            int bsLiveShadow = this.bsLive;
    725            int bsBuffShadow = this.bsBuff;
    726
    727            while (zvec > limit_zt[zn]) {
    728                zn++;
    729                while (bsLiveShadow < 1) {
    730                    final int thech = inShadow.read();
    731
    732                    if (thech >= 0) {
    733                        bsBuffShadow = (bsBuffShadow << 8) | thech;
    734                        bsLiveShadow += 8;
    735                        continue;
    736                    } else {
    737                        throw new IOException("unexpected end of stream");
    738                    }
    739                }
    740                bsLiveShadow--;
    741                zvec = (zvec << 1) | ((bsBuffShadow >> bsLiveShadow) & 1);
    742            }
    743
    744            this.bsLive = bsLiveShadow;
    745            this.bsBuff = bsBuffShadow;
    746
    747            return dataShadow.perm[zt][zvec - dataShadow.base[zt][zn]];
    748        }
    749
    750        private void setupBlock() throws IOException {
    751            if (this.data == null) {
    752                return;
    753            }
    754
    755            final int[] cftab = this.data.cftab;
    756            final int[] tt = this.data.initTT(this.last + 1);
    757            final byte[] ll8 = this.data.ll8;
    758            cftab[0] = 0;
    759            System.arraycopy(this.data.unzftab, 0, cftab, 1, 256);
    760
    761            for (int i = 1, c = cftab[0]; i <= 256; i++) {
    762                c += cftab[i];
    763                cftab[i] = c;
    764            }
    765
    766            for (int i = 0, lastShadow = this.last; i <= lastShadow; i++) {
    767                tt[cftab[ll8[i] & 0xff]++] = i;
    768            }
    769
    770            if ((this.origPtr < 0) || (this.origPtr >= tt.length)) {
    771                throw new IOException("stream corrupted");
    772            }
    773
    774            this.su_tPos = tt[this.origPtr];
    775            this.su_count = 0;
    776            this.su_i2 = 0;
    777            this.su_ch2 = 256; /* not a char and not EOF */
    778
    779            if (this.blockRandomised) {
    780                this.su_rNToGo = 0;
    781                this.su_rTPos = 0;
    782                setupRandPartA();
    783            } else {
    784                setupNoRandPartA();
    785            }
    786        }
    787
    788        private void setupRandPartA() throws IOException {
    789            if (this.su_i2 <= this.last) {
    790                this.su_chPrev = this.su_ch2;
    791                int su_ch2Shadow = this.data.ll8[this.su_tPos] & 0xff;
    792                this.su_tPos = this.data.tt[this.su_tPos];
    793                if (this.su_rNToGo == 0) {
    794                    this.su_rNToGo = Rand.rNums(this.su_rTPos) - 1;
    795                    if (++this.su_rTPos == 512) {
    796                        this.su_rTPos = 0;
    797                    }
    798                } else {
    799                    this.su_rNToGo--;
    800                }
    801                this.su_ch2 = su_ch2Shadow ^= (this.su_rNToGo == 1) ? 1 : 0;
    802                this.su_i2++;
    803                this.currentChar = su_ch2Shadow;
    804                this.currentState = RAND_PART_B_STATE;
    805                this.crc.updateCRC(su_ch2Shadow);
    806            } else {
    807                endBlock();
    808                initBlock();
    809                setupBlock();
    810            }
    811        }
    812
    813        private void setupNoRandPartA() throws IOException {
    814            if (this.su_i2 <= this.last) {
    815                this.su_chPrev = this.su_ch2;
    816                int su_ch2Shadow = this.data.ll8[this.su_tPos] & 0xff;
    817                this.su_ch2 = su_ch2Shadow;
    818                this.su_tPos = this.data.tt[this.su_tPos];
    819                this.su_i2++;
    820                this.currentChar = su_ch2Shadow;
    821                this.currentState = NO_RAND_PART_B_STATE;
    822                this.crc.updateCRC(su_ch2Shadow);
    823            } else {
    824                this.currentState = NO_RAND_PART_A_STATE;
    825                endBlock();
    826                initBlock();
    827                setupBlock();
    828            }
    829        }
    830
    831        private void setupRandPartB() throws IOException {
    832            if (this.su_ch2 != this.su_chPrev) {
    833                this.currentState = RAND_PART_A_STATE;
    834                this.su_count = 1;
    835                setupRandPartA();
    836            } else if (++this.su_count >= 4) {
    837                this.su_z = (char) (this.data.ll8[this.su_tPos] & 0xff);
    838                this.su_tPos = this.data.tt[this.su_tPos];
    839                if (this.su_rNToGo == 0) {
    840                    this.su_rNToGo = Rand.rNums(this.su_rTPos) - 1;
    841                    if (++this.su_rTPos == 512) {
    842                        this.su_rTPos = 0;
    843                    }
    844                } else {
    845                    this.su_rNToGo--;
    846                }
    847                this.su_j2 = 0;
    848                this.currentState = RAND_PART_C_STATE;
    849                if (this.su_rNToGo == 1) {
    850                    this.su_z ^= 1;
    851                }
    852                setupRandPartC();
    853            } else {
    854                this.currentState = RAND_PART_A_STATE;
    855                setupRandPartA();
    856            }
    857        }
    858
    859        private void setupRandPartC() throws IOException {
    860            if (this.su_j2 < this.su_z) {
    861                this.currentChar = this.su_ch2;
    862                this.crc.updateCRC(this.su_ch2);
    863                this.su_j2++;
    864            } else {
    865                this.currentState = RAND_PART_A_STATE;
    866                this.su_i2++;
    867                this.su_count = 0;
    868                setupRandPartA();
    869            }
    870        }
    871
    872        private void setupNoRandPartB() throws IOException {
    873            if (this.su_ch2 != this.su_chPrev) {
    874                this.su_count = 1;
    875                setupNoRandPartA();
    876            } else if (++this.su_count >= 4) {
    877                this.su_z = (char) (this.data.ll8[this.su_tPos] & 0xff);
    878                this.su_tPos = this.data.tt[this.su_tPos];
    879                this.su_j2 = 0;
    880                setupNoRandPartC();
    881            } else {
    882                setupNoRandPartA();
    883            }
    884        }
    885
    886        private void setupNoRandPartC() throws IOException {
    887            if (this.su_j2 < this.su_z) {
    888                int su_ch2Shadow = this.su_ch2;
    889                this.currentChar = su_ch2Shadow;
    890                this.crc.updateCRC(su_ch2Shadow);
    891                this.su_j2++;
    892                this.currentState = NO_RAND_PART_C_STATE;
    893            } else {
    894                this.su_i2++;
    895                this.su_count = 0;
    896                setupNoRandPartA();
    897            }
    898        }
    899
    900        private static final class Data extends Object {
    901
    902            // (with blockSize 900k)
    903            final boolean[] inUse = new boolean[256]; // 256 byte
    904
    905            final byte[] seqToUnseq = new byte[256]; // 256 byte
    906            final byte[] selector = new byte[MAX_SELECTORS]; // 18002 byte
    907            final byte[] selectorMtf = new byte[MAX_SELECTORS]; // 18002 byte
    908
    909            /**
    910             * Freq table collected to save a pass over the data during
    911             * decompression.
    912             */
    913            final int[] unzftab = new int[256]; // 1024 byte
    914
    915            final int[][] limit = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192 byte
    916            final int[][] base = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192 byte
    917            final int[][] perm = new int[N_GROUPS][MAX_ALPHA_SIZE]; // 6192 byte
    918            final int[] minLens = new int[N_GROUPS]; // 24 byte
    919
    920            final int[] cftab = new int[257]; // 1028 byte
    921            final char[] getAndMoveToFrontDecode_yy = new char[256]; // 512 byte
    922            final char[][] temp_charArray2d = new char[N_GROUPS][MAX_ALPHA_SIZE]; // 3096
    923            // byte
    924            final byte[] recvDecodingTables_pos = new byte[N_GROUPS]; // 6 byte
    925            // ---------------
    926            // 60798 byte
    927
    928            int[] tt; // 3600000 byte
    929            byte[] ll8; // 900000 byte
    930
    931            // ---------------
    932            // 4560782 byte
    933            // ===============
    934
    935            Data(int blockSize100k) {
    936                super();
    937
    938                this.ll8 = new byte[blockSize100k * BZip2Constants.BASEBLOCKSIZE];
    939            }
    940
    941            /**
    942             * Initializes the {@link #tt} array.
    943             *
    944             * This method is called when the required length of the array is known.
    945             * I don't initialize it at construction time to avoid unneccessary
    946             * memory allocation when compressing small files.
    947             */
    948            final int[] initTT(int length) {
    949                int[] ttShadow = this.tt;
    950
    951                // tt.length should always be >= length, but theoretically
    952                // it can happen, if the compressor mixed small and large
    953                // blocks. Normally only the last block will be smaller
    954                // than others.
    955                if ((ttShadow == null) || (ttShadow.length < length)) {
    956                    this.tt = ttShadow = new int[length];
    957                }
    958
    959                return ttShadow;
    960            }
    961
    962        }
    963
    964        /**
    965         * Checks if the signature matches what is expected for a bzip2 file.
    966         *
    967         * @param signature
    968         *            the bytes to check
    969         * @param length
    970         *            the number of bytes to check
    971         * @return true, if this stream is a bzip2 compressed stream, false otherwise
    972         *
    973         * @since Apache Commons Compress 1.1
    974         */
    975        public static boolean matches(byte[] signature, int length) {
    976
    977            if (length < 3) {
    978                return false;
    979            }
    980
    981            if (signature[0] != 'B') {
    982                return false;
    983            }
    984
    985            if (signature[1] != 'Z') {
    986                return false;
    987            }
    988
    989            if (signature[2] != 'h') {
    990                return false;
    991            }
    992
    993            return true;
    994        }
    995    }