LCOV - code coverage report
Current view: directory - modules/zlib/src - inftrees.c (source / functions) Found Hit Coverage
Test: app.info Lines: 123 100 81.3 %
Date: 2012-06-02 Functions: 1 1 100.0 %

       1                 : /* inftrees.c -- generate Huffman trees for efficient decoding
       2                 :  * Copyright (C) 1995-2010 Mark Adler
       3                 :  * For conditions of distribution and use, see copyright notice in zlib.h
       4                 :  */
       5                 : 
       6                 : #include "zutil.h"
       7                 : #include "inftrees.h"
       8                 : 
       9                 : #define MAXBITS 15
      10                 : 
      11                 : const char inflate_copyright[] =
      12                 :    " inflate 1.2.5 Copyright 1995-2010 Mark Adler ";
      13                 : /*
      14                 :   If you use the zlib library in a product, an acknowledgment is welcome
      15                 :   in the documentation of your product. If for some reason you cannot
      16                 :   include such an acknowledgment, I would appreciate that you keep this
      17                 :   copyright string in the executable of your product.
      18                 :  */
      19                 : 
      20                 : /*
      21                 :    Build a set of tables to decode the provided canonical Huffman code.
      22                 :    The code lengths are lens[0..codes-1].  The result starts at *table,
      23                 :    whose indices are 0..2^bits-1.  work is a writable array of at least
      24                 :    lens shorts, which is used as a work area.  type is the type of code
      25                 :    to be generated, CODES, LENS, or DISTS.  On return, zero is success,
      26                 :    -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
      27                 :    on return points to the next available entry's address.  bits is the
      28                 :    requested root table index bits, and on return it is the actual root
      29                 :    table index bits.  It will differ if the request is greater than the
      30                 :    longest code or if it is less than the shortest code.
      31                 :  */
      32            3285 : int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)
      33                 : codetype type;
      34                 : unsigned short FAR *lens;
      35                 : unsigned codes;
      36                 : code FAR * FAR *table;
      37                 : unsigned FAR *bits;
      38                 : unsigned short FAR *work;
      39                 : {
      40                 :     unsigned len;               /* a code's length in bits */
      41                 :     unsigned sym;               /* index of code symbols */
      42                 :     unsigned min, max;          /* minimum and maximum code lengths */
      43                 :     unsigned root;              /* number of index bits for root table */
      44                 :     unsigned curr;              /* number of index bits for current table */
      45                 :     unsigned drop;              /* code bits to drop for sub-table */
      46                 :     int left;                   /* number of prefix codes available */
      47                 :     unsigned used;              /* code entries in table used */
      48                 :     unsigned huff;              /* Huffman code */
      49                 :     unsigned incr;              /* for incrementing code, index */
      50                 :     unsigned fill;              /* index for replicating entries */
      51                 :     unsigned low;               /* low bits for current root entry */
      52                 :     unsigned mask;              /* mask for low root bits */
      53                 :     code here;                  /* table entry for duplication */
      54                 :     code FAR *next;             /* next available space in table */
      55                 :     const unsigned short FAR *base;     /* base value table to use */
      56                 :     const unsigned short FAR *extra;    /* extra bits table to use */
      57                 :     int end;                    /* use base and extra for symbol > end */
      58                 :     unsigned short count[MAXBITS+1];    /* number of codes of each length */
      59                 :     unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
      60                 :     static const unsigned short lbase[31] = { /* Length codes 257..285 base */
      61                 :         3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
      62                 :         35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
      63                 :     static const unsigned short lext[31] = { /* Length codes 257..285 extra */
      64                 :         16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
      65                 :         19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 73, 195};
      66                 :     static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
      67                 :         1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
      68                 :         257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
      69                 :         8193, 12289, 16385, 24577, 0, 0};
      70                 :     static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
      71                 :         16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
      72                 :         23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
      73                 :         28, 28, 29, 29, 64, 64};
      74                 : 
      75                 :     /*
      76                 :        Process a set of code lengths to create a canonical Huffman code.  The
      77                 :        code lengths are lens[0..codes-1].  Each length corresponds to the
      78                 :        symbols 0..codes-1.  The Huffman code is generated by first sorting the
      79                 :        symbols by length from short to long, and retaining the symbol order
      80                 :        for codes with equal lengths.  Then the code starts with all zero bits
      81                 :        for the first code of the shortest length, and the codes are integer
      82                 :        increments for the same length, and zeros are appended as the length
      83                 :        increases.  For the deflate format, these bits are stored backwards
      84                 :        from their more natural integer increment ordering, and so when the
      85                 :        decoding tables are built in the large loop below, the integer codes
      86                 :        are incremented backwards.
      87                 : 
      88                 :        This routine assumes, but does not check, that all of the entries in
      89                 :        lens[] are in the range 0..MAXBITS.  The caller must assure this.
      90                 :        1..MAXBITS is interpreted as that code length.  zero means that that
      91                 :        symbol does not occur in this code.
      92                 : 
      93                 :        The codes are sorted by computing a count of codes for each length,
      94                 :        creating from that a table of starting indices for each length in the
      95                 :        sorted table, and then entering the symbols in order in the sorted
      96                 :        table.  The sorted table is work[], with that space being provided by
      97                 :        the caller.
      98                 : 
      99                 :        The length counts are used for other purposes as well, i.e. finding
     100                 :        the minimum and maximum length codes, determining if there are any
     101                 :        codes at all, checking for a valid set of lengths, and looking ahead
     102                 :        at length counts to determine sub-table sizes when building the
     103                 :        decoding tables.
     104                 :      */
     105                 : 
     106                 :     /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
     107           55845 :     for (len = 0; len <= MAXBITS; len++)
     108           52560 :         count[len] = 0;
     109          344536 :     for (sym = 0; sym < codes; sym++)
     110          341251 :         count[lens[sym]]++;
     111                 : 
     112                 :     /* bound code lengths, force root to be within code lengths */
     113            3285 :     root = *bits;
     114           31390 :     for (max = MAXBITS; max >= 1; max--)
     115           31390 :         if (count[max] != 0) break;
     116            3285 :     if (root > max) root = max;
     117            3285 :     if (max == 0) {                     /* no symbols to code at all */
     118               0 :         here.op = (unsigned char)64;    /* invalid code marker */
     119               0 :         here.bits = (unsigned char)1;
     120               0 :         here.val = (unsigned short)0;
     121               0 :         *(*table)++ = here;             /* make a table to force an error */
     122               0 :         *(*table)++ = here;
     123               0 :         *bits = 1;
     124               0 :         return 0;     /* no symbols, but wait for decoding to report error */
     125                 :     }
     126            9030 :     for (min = 1; min < max; min++)
     127            9030 :         if (count[min] != 0) break;
     128            3285 :     if (root < min) root = min;
     129                 : 
     130                 :     /* check for an over-subscribed or incomplete set of lengths */
     131            3285 :     left = 1;
     132           52560 :     for (len = 1; len <= MAXBITS; len++) {
     133           49275 :         left <<= 1;
     134           49275 :         left -= count[len];
     135           49275 :         if (left < 0) return -1;        /* over-subscribed */
     136                 :     }
     137            3285 :     if (left > 0 && (type == CODES || max != 1))
     138               0 :         return -1;                      /* incomplete set */
     139                 : 
     140                 :     /* generate offsets into symbol table for each length for sorting */
     141            3285 :     offs[1] = 0;
     142           49275 :     for (len = 1; len < MAXBITS; len++)
     143           45990 :         offs[len + 1] = offs[len] + count[len];
     144                 : 
     145                 :     /* sort symbols by length, by symbol order within each length */
     146          344536 :     for (sym = 0; sym < codes; sym++)
     147          341251 :         if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
     148                 : 
     149                 :     /*
     150                 :        Create and fill in decoding tables.  In this loop, the table being
     151                 :        filled is at next and has curr index bits.  The code being used is huff
     152                 :        with length len.  That code is converted to an index by dropping drop
     153                 :        bits off of the bottom.  For codes where len is less than drop + curr,
     154                 :        those top drop + curr - len bits are incremented through all values to
     155                 :        fill the table with replicated entries.
     156                 : 
     157                 :        root is the number of index bits for the root table.  When len exceeds
     158                 :        root, sub-tables are created pointed to by the root entry with an index
     159                 :        of the low root bits of huff.  This is saved in low to check for when a
     160                 :        new sub-table should be started.  drop is zero when the root table is
     161                 :        being filled, and drop is root when sub-tables are being filled.
     162                 : 
     163                 :        When a new sub-table is needed, it is necessary to look ahead in the
     164                 :        code lengths to determine what size sub-table is needed.  The length
     165                 :        counts are used for this, and so count[] is decremented as codes are
     166                 :        entered in the tables.
     167                 : 
     168                 :        used keeps track of how many table entries have been allocated from the
     169                 :        provided *table space.  It is checked for LENS and DIST tables against
     170                 :        the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
     171                 :        the initial root table size constants.  See the comments in inftrees.h
     172                 :        for more information.
     173                 : 
     174                 :        sym increments through all symbols, and the loop terminates when
     175                 :        all codes of length max, i.e. all codes, have been processed.  This
     176                 :        routine permits incomplete codes, so another loop after this one fills
     177                 :        in the rest of the decoding tables with invalid code markers.
     178                 :      */
     179                 : 
     180                 :     /* set up for code type */
     181            3285 :     switch (type) {
     182                 :     case CODES:
     183            1095 :         base = extra = work;    /* dummy value--not used */
     184            1095 :         end = 19;
     185            1095 :         break;
     186                 :     case LENS:
     187            1095 :         base = lbase;
     188            1095 :         base -= 257;
     189            1095 :         extra = lext;
     190            1095 :         extra -= 257;
     191            1095 :         end = 256;
     192            1095 :         break;
     193                 :     default:            /* DISTS */
     194            1095 :         base = dbase;
     195            1095 :         extra = dext;
     196            1095 :         end = -1;
     197                 :     }
     198                 : 
     199                 :     /* initialize state for loop */
     200            3285 :     huff = 0;                   /* starting code */
     201            3285 :     sym = 0;                    /* starting code symbol */
     202            3285 :     len = min;                  /* starting code length */
     203            3285 :     next = *table;              /* current table to fill in */
     204            3285 :     curr = root;                /* current table index bits */
     205            3285 :     drop = 0;                   /* current bits to drop from code for index */
     206            3285 :     low = (unsigned)(-1);       /* trigger new sub-table when len > root */
     207            3285 :     used = 1U << root;          /* use root table entries */
     208            3285 :     mask = used - 1;            /* mask for comparing low */
     209                 : 
     210                 :     /* check available table space */
     211            3285 :     if ((type == LENS && used >= ENOUGH_LENS) ||
     212            1095 :         (type == DISTS && used >= ENOUGH_DISTS))
     213               0 :         return 1;
     214                 : 
     215                 :     /* process all codes and make table entries */
     216                 :     for (;;) {
     217                 :         /* create table entry */
     218          100195 :         here.bits = (unsigned char)(len - drop);
     219          100195 :         if ((int)(work[sym]) < end) {
     220           70284 :             here.op = (unsigned char)0;
     221           70284 :             here.val = work[sym];
     222                 :         }
     223           29911 :         else if ((int)(work[sym]) > end) {
     224           28816 :             here.op = (unsigned char)(extra[work[sym]]);
     225           28816 :             here.val = base[work[sym]];
     226                 :         }
     227                 :         else {
     228            1095 :             here.op = (unsigned char)(32 + 64);         /* end of block */
     229            1095 :             here.val = 0;
     230                 :         }
     231                 : 
     232                 :         /* replicate for those indices with low len bits equal to huff */
     233          100195 :         incr = 1U << (len - drop);
     234          100195 :         fill = 1U << curr;
     235          100195 :         min = fill;                 /* save offset to next table */
     236                 :         do {
     237          418034 :             fill -= incr;
     238          418034 :             next[(huff >> drop) + fill] = here;
     239          418034 :         } while (fill != 0);
     240                 : 
     241                 :         /* backwards increment the len-bit code huff */
     242          100195 :         incr = 1U << (len - 1);
     243          297300 :         while (huff & incr)
     244           96910 :             incr >>= 1;
     245          100195 :         if (incr != 0) {
     246           96910 :             huff &= incr - 1;
     247           96910 :             huff += incr;
     248                 :         }
     249                 :         else
     250            3285 :             huff = 0;
     251                 : 
     252                 :         /* go to next symbol, update count, len */
     253          100195 :         sym++;
     254          100195 :         if (--(count[len]) == 0) {
     255           15187 :             if (len == max) break;
     256           11902 :             len = lens[work[sym]];
     257                 :         }
     258                 : 
     259                 :         /* create new sub-table if needed */
     260           96910 :         if (len > root && (huff & mask) != low) {
     261                 :             /* if first time, transition to sub-tables */
     262             120 :             if (drop == 0)
     263              20 :                 drop = root;
     264                 : 
     265                 :             /* increment past last table */
     266             120 :             next += min;            /* here min is 1 << curr */
     267                 : 
     268                 :             /* determine length of next table */
     269             120 :             curr = len - drop;
     270             120 :             left = (int)(1 << curr);
     271             245 :             while (curr + drop < max) {
     272              85 :                 left -= count[curr + drop];
     273              85 :                 if (left <= 0) break;
     274               5 :                 curr++;
     275               5 :                 left <<= 1;
     276                 :             }
     277                 : 
     278                 :             /* check for enough space */
     279             120 :             used += 1U << curr;
     280             120 :             if ((type == LENS && used >= ENOUGH_LENS) ||
     281              21 :                 (type == DISTS && used >= ENOUGH_DISTS))
     282               0 :                 return 1;
     283                 : 
     284                 :             /* point entry in root table to sub-table */
     285             120 :             low = huff & mask;
     286             120 :             (*table)[low].op = (unsigned char)curr;
     287             120 :             (*table)[low].bits = (unsigned char)root;
     288             120 :             (*table)[low].val = (unsigned short)(next - *table);
     289                 :         }
     290           96910 :     }
     291                 : 
     292                 :     /*
     293                 :        Fill in rest of table for incomplete codes.  This loop is similar to the
     294                 :        loop above in incrementing huff for table indices.  It is assumed that
     295                 :        len is equal to curr + drop, so there is no loop needed to increment
     296                 :        through high index bits.  When the current sub-table is filled, the loop
     297                 :        drops back to the root table to fill in any remaining entries there.
     298                 :      */
     299            3285 :     here.op = (unsigned char)64;                /* invalid code marker */
     300            3285 :     here.bits = (unsigned char)(len - drop);
     301            3285 :     here.val = (unsigned short)0;
     302            6570 :     while (huff != 0) {
     303                 :         /* when done with sub-table, drop back to root table */
     304               0 :         if (drop != 0 && (huff & mask) != low) {
     305               0 :             drop = 0;
     306               0 :             len = root;
     307               0 :             next = *table;
     308               0 :             here.bits = (unsigned char)len;
     309                 :         }
     310                 : 
     311                 :         /* put invalid code marker in table */
     312               0 :         next[huff >> drop] = here;
     313                 : 
     314                 :         /* backwards increment the len-bit code huff */
     315               0 :         incr = 1U << (len - 1);
     316               0 :         while (huff & incr)
     317               0 :             incr >>= 1;
     318               0 :         if (incr != 0) {
     319               0 :             huff &= incr - 1;
     320               0 :             huff += incr;
     321                 :         }
     322                 :         else
     323               0 :             huff = 0;
     324                 :     }
     325                 : 
     326                 :     /* set return parameters */
     327            3285 :     *table += used;
     328            3285 :     *bits = root;
     329            3285 :     return 0;
     330                 : }

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