1 /*

     2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     3  *

     4  * This code is free software; you can redistribute it and/or modify it

     5  * under the terms of the GNU General Public License version 2 only, as

     6  * published by the Free Software Foundation.  Oracle designates this

     7  * particular file as subject to the "Classpath" exception as provided

     8  * by Oracle in the LICENSE file that accompanied this code.

     9  *

    10  * This code is distributed in the hope that it will be useful, but WITHOUT

    11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    13  * version 2 for more details (a copy is included in the LICENSE file that

    14  * accompanied this code).

    15  *

    16  * You should have received a copy of the GNU General Public License version

    17  * 2 along with this work; if not, write to the Free Software Foundation,

    18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    19  *

    20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    21  * or visit www.oracle.com if you need additional information or have any

    22  * questions.

    23  */

    24 

    25 /* inftrees.c -- generate Huffman trees for efficient decoding

    26  * Copyright (C) 1995-2013 Mark Adler

    27  * For conditions of distribution and use, see copyright notice in zlib.h

    28  */

    29 

    30 #include "zutil.h"

    31 #include "inftrees.h"

    32 

    33 #define MAXBITS 15

    34 

    35 const char inflate_copyright[] =

    36    " inflate 1.2.8 Copyright 1995-2013 Mark Adler ";

    37 /*

    38   If you use the zlib library in a product, an acknowledgment is welcome

    39   in the documentation of your product. If for some reason you cannot

    40   include such an acknowledgment, I would appreciate that you keep this

    41   copyright string in the executable of your product.

    42  */

    43 

    44 /*

    45    Build a set of tables to decode the provided canonical Huffman code.

    46    The code lengths are lens[0..codes-1].  The result starts at *table,

    47    whose indices are 0..2^bits-1.  work is a writable array of at least

    48    lens shorts, which is used as a work area.  type is the type of code

    49    to be generated, CODES, LENS, or DISTS.  On return, zero is success,

    50    -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table

    51    on return points to the next available entry's address.  bits is the

    52    requested root table index bits, and on return it is the actual root

    53    table index bits.  It will differ if the request is greater than the

    54    longest code or if it is less than the shortest code.

    55  */

    56 int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)

    57 codetype type;

    58 unsigned short FAR *lens;

    59 unsigned codes;

    60 code FAR * FAR *table;

    61 unsigned FAR *bits;

    62 unsigned short FAR *work;

    63 {

    64     unsigned len;               /* a code's length in bits */

    65     unsigned sym;               /* index of code symbols */

    66     unsigned min, max;          /* minimum and maximum code lengths */

    67     unsigned root;              /* number of index bits for root table */

    68     unsigned curr;              /* number of index bits for current table */

    69     unsigned drop;              /* code bits to drop for sub-table */

    70     int left;                   /* number of prefix codes available */

    71     unsigned used;              /* code entries in table used */

    72     unsigned huff;              /* Huffman code */

    73     unsigned incr;              /* for incrementing code, index */

    74     unsigned fill;              /* index for replicating entries */

    75     unsigned low;               /* low bits for current root entry */

    76     unsigned mask;              /* mask for low root bits */

    77     code here;                  /* table entry for duplication */

    78     code FAR *next;             /* next available space in table */

    79     const unsigned short FAR *base;     /* base value table to use */

    80     const unsigned short FAR *extra;    /* extra bits table to use */

    81     int end;                    /* use base and extra for symbol > end */

    82     unsigned short count[MAXBITS+1];    /* number of codes of each length */

    83     unsigned short offs[MAXBITS+1];     /* offsets in table for each length */

    84     static const unsigned short lbase[31] = { /* Length codes 257..285 base */

    85         3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,

    86         35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};

    87     static const unsigned short lext[31] = { /* Length codes 257..285 extra */

    88         16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,

    89         19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 72, 78};

    90     static const unsigned short dbase[32] = { /* Distance codes 0..29 base */

    91         1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,

    92         257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,

    93         8193, 12289, 16385, 24577, 0, 0};

    94     static const unsigned short dext[32] = { /* Distance codes 0..29 extra */

    95         16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,

    96         23, 23, 24, 24, 25, 25, 26, 26, 27, 27,

    97         28, 28, 29, 29, 64, 64};

    98 

    99     /*

   100        Process a set of code lengths to create a canonical Huffman code.  The

   101        code lengths are lens[0..codes-1].  Each length corresponds to the

   102        symbols 0..codes-1.  The Huffman code is generated by first sorting the

   103        symbols by length from short to long, and retaining the symbol order

   104        for codes with equal lengths.  Then the code starts with all zero bits

   105        for the first code of the shortest length, and the codes are integer

   106        increments for the same length, and zeros are appended as the length

   107        increases.  For the deflate format, these bits are stored backwards

   108        from their more natural integer increment ordering, and so when the

   109        decoding tables are built in the large loop below, the integer codes

   110        are incremented backwards.

   111 

   112        This routine assumes, but does not check, that all of the entries in

   113        lens[] are in the range 0..MAXBITS.  The caller must assure this.

   114        1..MAXBITS is interpreted as that code length.  zero means that that

   115        symbol does not occur in this code.

   116 

   117        The codes are sorted by computing a count of codes for each length,

   118        creating from that a table of starting indices for each length in the

   119        sorted table, and then entering the symbols in order in the sorted

   120        table.  The sorted table is work[], with that space being provided by

   121        the caller.

   122 

   123        The length counts are used for other purposes as well, i.e. finding

   124        the minimum and maximum length codes, determining if there are any

   125        codes at all, checking for a valid set of lengths, and looking ahead

   126        at length counts to determine sub-table sizes when building the

   127        decoding tables.

   128      */

   129 

   130     /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */

   131     for (len = 0; len <= MAXBITS; len++)

   132         count[len] = 0;

   133     for (sym = 0; sym < codes; sym++)

   134         count[lens[sym]]++;

   135 

   136     /* bound code lengths, force root to be within code lengths */

   137     root = *bits;

   138     for (max = MAXBITS; max >= 1; max--)

   139         if (count[max] != 0) break;

   140     if (root > max) root = max;

   141     if (max == 0) {                     /* no symbols to code at all */

   142         here.op = (unsigned char)64;    /* invalid code marker */

   143         here.bits = (unsigned char)1;

   144         here.val = (unsigned short)0;

   145         *(*table)++ = here;             /* make a table to force an error */

   146         *(*table)++ = here;

   147         *bits = 1;

   148         return 0;     /* no symbols, but wait for decoding to report error */

   149     }

   150     for (min = 1; min < max; min++)

   151         if (count[min] != 0) break;

   152     if (root < min) root = min;

   153 

   154     /* check for an over-subscribed or incomplete set of lengths */

   155     left = 1;

   156     for (len = 1; len <= MAXBITS; len++) {

   157         left <<= 1;

   158         left -= count[len];

   159         if (left < 0) return -1;        /* over-subscribed */

   160     }

   161     if (left > 0 && (type == CODES || max != 1))

   162         return -1;                      /* incomplete set */

   163 

   164     /* generate offsets into symbol table for each length for sorting */

   165     offs[1] = 0;

   166     for (len = 1; len < MAXBITS; len++)

   167         offs[len + 1] = offs[len] + count[len];

   168 

   169     /* sort symbols by length, by symbol order within each length */

   170     for (sym = 0; sym < codes; sym++)

   171         if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;

   172 

   173     /*

   174        Create and fill in decoding tables.  In this loop, the table being

   175        filled is at next and has curr index bits.  The code being used is huff

   176        with length len.  That code is converted to an index by dropping drop

   177        bits off of the bottom.  For codes where len is less than drop + curr,

   178        those top drop + curr - len bits are incremented through all values to

   179        fill the table with replicated entries.

   180 

   181        root is the number of index bits for the root table.  When len exceeds

   182        root, sub-tables are created pointed to by the root entry with an index

   183        of the low root bits of huff.  This is saved in low to check for when a

   184        new sub-table should be started.  drop is zero when the root table is

   185        being filled, and drop is root when sub-tables are being filled.

   186 

   187        When a new sub-table is needed, it is necessary to look ahead in the

   188        code lengths to determine what size sub-table is needed.  The length

   189        counts are used for this, and so count[] is decremented as codes are

   190        entered in the tables.

   191 

   192        used keeps track of how many table entries have been allocated from the

   193        provided *table space.  It is checked for LENS and DIST tables against

   194        the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in

   195        the initial root table size constants.  See the comments in inftrees.h

   196        for more information.

   197 

   198        sym increments through all symbols, and the loop terminates when

   199        all codes of length max, i.e. all codes, have been processed.  This

   200        routine permits incomplete codes, so another loop after this one fills

   201        in the rest of the decoding tables with invalid code markers.

   202      */

   203 

   204     /* set up for code type */

   205     switch (type) {

   206     case CODES:

   207         base = extra = work;    /* dummy value--not used */

   208         end = 19;

   209         break;

   210     case LENS:

   211         base = lbase;

   212         base -= 257;

   213         extra = lext;

   214         extra -= 257;

   215         end = 256;

   216         break;

   217     default:            /* DISTS */

   218         base = dbase;

   219         extra = dext;

   220         end = -1;

   221     }

   222 

   223     /* initialize state for loop */

   224     huff = 0;                   /* starting code */

   225     sym = 0;                    /* starting code symbol */

   226     len = min;                  /* starting code length */

   227     next = *table;              /* current table to fill in */

   228     curr = root;                /* current table index bits */

   229     drop = 0;                   /* current bits to drop from code for index */

   230     low = (unsigned)(-1);       /* trigger new sub-table when len > root */

   231     used = 1U << root;          /* use root table entries */

   232     mask = used - 1;            /* mask for comparing low */

   233 

   234     /* check available table space */

   235     if ((type == LENS && used > ENOUGH_LENS) ||

   236         (type == DISTS && used > ENOUGH_DISTS))

   237         return 1;

   238 

   239     /* process all codes and make table entries */

   240     for (;;) {

   241         /* create table entry */

   242         here.bits = (unsigned char)(len - drop);

   243         if ((int)(work[sym]) < end) {

   244             here.op = (unsigned char)0;

   245             here.val = work[sym];

   246         }

   247         else if ((int)(work[sym]) > end) {

   248             here.op = (unsigned char)(extra[work[sym]]);

   249             here.val = base[work[sym]];

   250         }

   251         else {

   252             here.op = (unsigned char)(32 + 64);         /* end of block */

   253             here.val = 0;

   254         }

   255 

   256         /* replicate for those indices with low len bits equal to huff */

   257         incr = 1U << (len - drop);

   258         fill = 1U << curr;

   259         min = fill;                 /* save offset to next table */

   260         do {

   261             fill -= incr;

   262             next[(huff >> drop) + fill] = here;

   263         } while (fill != 0);

   264 

   265         /* backwards increment the len-bit code huff */

   266         incr = 1U << (len - 1);

   267         while (huff & incr)

   268             incr >>= 1;

   269         if (incr != 0) {

   270             huff &= incr - 1;

   271             huff += incr;

   272         }

   273         else

   274             huff = 0;

   275 

   276         /* go to next symbol, update count, len */

   277         sym++;

   278         if (--(count[len]) == 0) {

   279             if (len == max) break;

   280             len = lens[work[sym]];

   281         }

   282 

   283         /* create new sub-table if needed */

   284         if (len > root && (huff & mask) != low) {

   285             /* if first time, transition to sub-tables */

   286             if (drop == 0)

   287                 drop = root;

   288 

   289             /* increment past last table */

   290             next += min;            /* here min is 1 << curr */

   291 

   292             /* determine length of next table */

   293             curr = len - drop;

   294             left = (int)(1 << curr);

   295             while (curr + drop < max) {

   296                 left -= count[curr + drop];

   297                 if (left <= 0) break;

   298                 curr++;

   299                 left <<= 1;

   300             }

   301 

   302             /* check for enough space */

   303             used += 1U << curr;

   304             if ((type == LENS && used > ENOUGH_LENS) ||

   305                 (type == DISTS && used > ENOUGH_DISTS))

   306                 return 1;

   307 

   308             /* point entry in root table to sub-table */

   309             low = huff & mask;

   310             (*table)[low].op = (unsigned char)curr;

   311             (*table)[low].bits = (unsigned char)root;

   312             (*table)[low].val = (unsigned short)(next - *table);

   313         }

   314     }

   315 

   316     /* fill in remaining table entry if code is incomplete (guaranteed to have

   317        at most one remaining entry, since if the code is incomplete, the

   318        maximum code length that was allowed to get this far is one bit) */

   319     if (huff != 0) {

   320         here.op = (unsigned char)64;            /* invalid code marker */

   321         here.bits = (unsigned char)(len - drop);

   322         here.val = (unsigned short)0;

   323         next[huff] = here;

   324     }

   325 

   326     /* set return parameters */

   327     *table += used;

   328     *bits = root;

   329     return 0;

   330 }