linux/lib/zlib_inflate/inftrees.c
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   1/* inftrees.c -- generate Huffman trees for efficient decoding
   2 * Copyright (C) 1995-2005 Mark Adler
   3 * For conditions of distribution and use, see copyright notice in zlib.h
   4 */
   5
   6#include <linux/zutil.h>
   7#include "inftrees.h"
   8
   9#define MAXBITS 15
  10
  11/*
  12   Build a set of tables to decode the provided canonical Huffman code.
  13   The code lengths are lens[0..codes-1].  The result starts at *table,
  14   whose indices are 0..2^bits-1.  work is a writable array of at least
  15   lens shorts, which is used as a work area.  type is the type of code
  16   to be generated, CODES, LENS, or DISTS.  On return, zero is success,
  17   -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
  18   on return points to the next available entry's address.  bits is the
  19   requested root table index bits, and on return it is the actual root
  20   table index bits.  It will differ if the request is greater than the
  21   longest code or if it is less than the shortest code.
  22 */
  23int zlib_inflate_table(codetype type, unsigned short *lens, unsigned codes,
  24                        code **table, unsigned *bits, unsigned short *work)
  25{
  26    unsigned len;               /* a code's length in bits */
  27    unsigned sym;               /* index of code symbols */
  28    unsigned min, max;          /* minimum and maximum code lengths */
  29    unsigned root;              /* number of index bits for root table */
  30    unsigned curr;              /* number of index bits for current table */
  31    unsigned drop;              /* code bits to drop for sub-table */
  32    int left;                   /* number of prefix codes available */
  33    unsigned used;              /* code entries in table used */
  34    unsigned huff;              /* Huffman code */
  35    unsigned incr;              /* for incrementing code, index */
  36    unsigned fill;              /* index for replicating entries */
  37    unsigned low;               /* low bits for current root entry */
  38    unsigned mask;              /* mask for low root bits */
  39    code this;                  /* table entry for duplication */
  40    code *next;             /* next available space in table */
  41    const unsigned short *base;     /* base value table to use */
  42    const unsigned short *extra;    /* extra bits table to use */
  43    int end;                    /* use base and extra for symbol > end */
  44    unsigned short count[MAXBITS+1];    /* number of codes of each length */
  45    unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
  46    static const unsigned short lbase[31] = { /* Length codes 257..285 base */
  47        3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
  48        35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
  49    static const unsigned short lext[31] = { /* Length codes 257..285 extra */
  50        16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
  51        19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 201, 196};
  52    static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
  53        1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
  54        257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
  55        8193, 12289, 16385, 24577, 0, 0};
  56    static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
  57        16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
  58        23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
  59        28, 28, 29, 29, 64, 64};
  60
  61    /*
  62       Process a set of code lengths to create a canonical Huffman code.  The
  63       code lengths are lens[0..codes-1].  Each length corresponds to the
  64       symbols 0..codes-1.  The Huffman code is generated by first sorting the
  65       symbols by length from short to long, and retaining the symbol order
  66       for codes with equal lengths.  Then the code starts with all zero bits
  67       for the first code of the shortest length, and the codes are integer
  68       increments for the same length, and zeros are appended as the length
  69       increases.  For the deflate format, these bits are stored backwards
  70       from their more natural integer increment ordering, and so when the
  71       decoding tables are built in the large loop below, the integer codes
  72       are incremented backwards.
  73
  74       This routine assumes, but does not check, that all of the entries in
  75       lens[] are in the range 0..MAXBITS.  The caller must assure this.
  76       1..MAXBITS is interpreted as that code length.  zero means that that
  77       symbol does not occur in this code.
  78
  79       The codes are sorted by computing a count of codes for each length,
  80       creating from that a table of starting indices for each length in the
  81       sorted table, and then entering the symbols in order in the sorted
  82       table.  The sorted table is work[], with that space being provided by
  83       the caller.
  84
  85       The length counts are used for other purposes as well, i.e. finding
  86       the minimum and maximum length codes, determining if there are any
  87       codes at all, checking for a valid set of lengths, and looking ahead
  88       at length counts to determine sub-table sizes when building the
  89       decoding tables.
  90     */
  91
  92    /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
  93    for (len = 0; len <= MAXBITS; len++)
  94        count[len] = 0;
  95    for (sym = 0; sym < codes; sym++)
  96        count[lens[sym]]++;
  97
  98    /* bound code lengths, force root to be within code lengths */
  99    root = *bits;
 100    for (max = MAXBITS; max >= 1; max--)
 101        if (count[max] != 0) break;
 102    if (root > max) root = max;
 103    if (max == 0) {                     /* no symbols to code at all */
 104        this.op = (unsigned char)64;    /* invalid code marker */
 105        this.bits = (unsigned char)1;
 106        this.val = (unsigned short)0;
 107        *(*table)++ = this;             /* make a table to force an error */
 108        *(*table)++ = this;
 109        *bits = 1;
 110        return 0;     /* no symbols, but wait for decoding to report error */
 111    }
 112    for (min = 1; min <= MAXBITS; min++)
 113        if (count[min] != 0) break;
 114    if (root < min) root = min;
 115
 116    /* check for an over-subscribed or incomplete set of lengths */
 117    left = 1;
 118    for (len = 1; len <= MAXBITS; len++) {
 119        left <<= 1;
 120        left -= count[len];
 121        if (left < 0) return -1;        /* over-subscribed */
 122    }
 123    if (left > 0 && (type == CODES || max != 1))
 124        return -1;                      /* incomplete set */
 125
 126    /* generate offsets into symbol table for each length for sorting */
 127    offs[1] = 0;
 128    for (len = 1; len < MAXBITS; len++)
 129        offs[len + 1] = offs[len] + count[len];
 130
 131    /* sort symbols by length, by symbol order within each length */
 132    for (sym = 0; sym < codes; sym++)
 133        if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
 134
 135    /*
 136       Create and fill in decoding tables.  In this loop, the table being
 137       filled is at next and has curr index bits.  The code being used is huff
 138       with length len.  That code is converted to an index by dropping drop
 139       bits off of the bottom.  For codes where len is less than drop + curr,
 140       those top drop + curr - len bits are incremented through all values to
 141       fill the table with replicated entries.
 142
 143       root is the number of index bits for the root table.  When len exceeds
 144       root, sub-tables are created pointed to by the root entry with an index
 145       of the low root bits of huff.  This is saved in low to check for when a
 146       new sub-table should be started.  drop is zero when the root table is
 147       being filled, and drop is root when sub-tables are being filled.
 148
 149       When a new sub-table is needed, it is necessary to look ahead in the
 150       code lengths to determine what size sub-table is needed.  The length
 151       counts are used for this, and so count[] is decremented as codes are
 152       entered in the tables.
 153
 154       used keeps track of how many table entries have been allocated from the
 155       provided *table space.  It is checked when a LENS table is being made
 156       against the space in *table, ENOUGH, minus the maximum space needed by
 157       the worst case distance code, MAXD.  This should never happen, but the
 158       sufficiency of ENOUGH has not been proven exhaustively, hence the check.
 159       This assumes that when type == LENS, bits == 9.
 160
 161       sym increments through all symbols, and the loop terminates when
 162       all codes of length max, i.e. all codes, have been processed.  This
 163       routine permits incomplete codes, so another loop after this one fills
 164       in the rest of the decoding tables with invalid code markers.
 165     */
 166
 167    /* set up for code type */
 168    switch (type) {
 169    case CODES:
 170        base = extra = work;    /* dummy value--not used */
 171        end = 19;
 172        break;
 173    case LENS:
 174        base = lbase;
 175        base -= 257;
 176        extra = lext;
 177        extra -= 257;
 178        end = 256;
 179        break;
 180    default:            /* DISTS */
 181        base = dbase;
 182        extra = dext;
 183        end = -1;
 184    }
 185
 186    /* initialize state for loop */
 187    huff = 0;                   /* starting code */
 188    sym = 0;                    /* starting code symbol */
 189    len = min;                  /* starting code length */
 190    next = *table;              /* current table to fill in */
 191    curr = root;                /* current table index bits */
 192    drop = 0;                   /* current bits to drop from code for index */
 193    low = (unsigned)(-1);       /* trigger new sub-table when len > root */
 194    used = 1U << root;          /* use root table entries */
 195    mask = used - 1;            /* mask for comparing low */
 196
 197    /* check available table space */
 198    if (type == LENS && used >= ENOUGH - MAXD)
 199        return 1;
 200
 201    /* process all codes and make table entries */
 202    for (;;) {
 203        /* create table entry */
 204        this.bits = (unsigned char)(len - drop);
 205        if ((int)(work[sym]) < end) {
 206            this.op = (unsigned char)0;
 207            this.val = work[sym];
 208        }
 209        else if ((int)(work[sym]) > end) {
 210            this.op = (unsigned char)(extra[work[sym]]);
 211            this.val = base[work[sym]];
 212        }
 213        else {
 214            this.op = (unsigned char)(32 + 64);         /* end of block */
 215            this.val = 0;
 216        }
 217
 218        /* replicate for those indices with low len bits equal to huff */
 219        incr = 1U << (len - drop);
 220        fill = 1U << curr;
 221        min = fill;                 /* save offset to next table */
 222        do {
 223            fill -= incr;
 224            next[(huff >> drop) + fill] = this;
 225        } while (fill != 0);
 226
 227        /* backwards increment the len-bit code huff */
 228        incr = 1U << (len - 1);
 229        while (huff & incr)
 230            incr >>= 1;
 231        if (incr != 0) {
 232            huff &= incr - 1;
 233            huff += incr;
 234        }
 235        else
 236            huff = 0;
 237
 238        /* go to next symbol, update count, len */
 239        sym++;
 240        if (--(count[len]) == 0) {
 241            if (len == max) break;
 242            len = lens[work[sym]];
 243        }
 244
 245        /* create new sub-table if needed */
 246        if (len > root && (huff & mask) != low) {
 247            /* if first time, transition to sub-tables */
 248            if (drop == 0)
 249                drop = root;
 250
 251            /* increment past last table */
 252            next += min;            /* here min is 1 << curr */
 253
 254            /* determine length of next table */
 255            curr = len - drop;
 256            left = (int)(1 << curr);
 257            while (curr + drop < max) {
 258                left -= count[curr + drop];
 259                if (left <= 0) break;
 260                curr++;
 261                left <<= 1;
 262            }
 263
 264            /* check for enough space */
 265            used += 1U << curr;
 266            if (type == LENS && used >= ENOUGH - MAXD)
 267                return 1;
 268
 269            /* point entry in root table to sub-table */
 270            low = huff & mask;
 271            (*table)[low].op = (unsigned char)curr;
 272            (*table)[low].bits = (unsigned char)root;
 273            (*table)[low].val = (unsigned short)(next - *table);
 274        }
 275    }
 276
 277    /*
 278       Fill in rest of table for incomplete codes.  This loop is similar to the
 279       loop above in incrementing huff for table indices.  It is assumed that
 280       len is equal to curr + drop, so there is no loop needed to increment
 281       through high index bits.  When the current sub-table is filled, the loop
 282       drops back to the root table to fill in any remaining entries there.
 283     */
 284    this.op = (unsigned char)64;                /* invalid code marker */
 285    this.bits = (unsigned char)(len - drop);
 286    this.val = (unsigned short)0;
 287    while (huff != 0) {
 288        /* when done with sub-table, drop back to root table */
 289        if (drop != 0 && (huff & mask) != low) {
 290            drop = 0;
 291            len = root;
 292            next = *table;
 293            this.bits = (unsigned char)len;
 294        }
 295
 296        /* put invalid code marker in table */
 297        next[huff >> drop] = this;
 298
 299        /* backwards increment the len-bit code huff */
 300        incr = 1U << (len - 1);
 301        while (huff & incr)
 302            incr >>= 1;
 303        if (incr != 0) {
 304            huff &= incr - 1;
 305            huff += incr;
 306        }
 307        else
 308            huff = 0;
 309    }
 310
 311    /* set return parameters */
 312    *table += used;
 313    *bits = root;
 314    return 0;
 315}
 316
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