libkern/zlib/inftrees.c

   1 /*
   2  * Copyright (c) 2008-2016, 2020 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
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  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
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  27  */
  28 /* inftrees.c -- generate Huffman trees for efficient decoding
  29  * Copyright (C) 1995-2005 Mark Adler
  30  * For conditions of distribution and use, see copyright notice in zlib.h
  31  */
  32
  33 #include "zutil.h"
  34 #include "inftrees.h"
  35
  36 #define MAXBITS 15
  37
  38 const char inflate_copyright[] =
  39    " inflate 1.2.3 Copyright 1995-2005 Mark Adler ";
  40 /*
  41   If you use the zlib library in a product, an acknowledgment is welcome
  42   in the documentation of your product. If for some reason you cannot
  43   include such an acknowledgment, I would appreciate that you keep this
  44   copyright string in the executable of your product.
  45  */
  46
  47 /*
  48    Build a set of tables to decode the provided canonical Huffman code.
  49    The code lengths are lens[0..codes-1].  The result starts at *table,
  50    whose indices are 0..2^bits-1.  work is a writable array of at least
  51    lens shorts, which is used as a work area.  type is the type of code
  52    to be generated, CODES, LENS, or DISTS.  On return, zero is success,
  53    -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
  54    on return points to the next available entry's address.  bits is the
  55    requested root table index bits, and on return it is the actual root
  56    table index bits.  It will differ if the request is greater than the
  57    longest code or if it is less than the shortest code.
  58  */
  59 int
  60 inflate_table(codetype type, unsigned short FAR *lens, unsigned codes,
  61               code FAR * FAR *table, 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 this;                  /* 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     unsigned match;             /* use base and extra for symbol >= match */
  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, 201, 196};
  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         this.op = (unsigned char)64;    /* invalid code marker */
 143         this.bits = (unsigned char)1;
 144         this.val = (unsigned short)0;
 145         *(*table)++ = this;             /* make a table to force an error */
 146         *(*table)++ = this;
 147         *bits = 1;
 148         return 0;     /* no symbols, but wait for decoding to report error */
 149     }
 150     for (min = 1; min <= MAXBITS; 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 when a LENS table is being made
 194        against the space in *table, ENOUGH, minus the maximum space needed by
 195        the worst case distance code, MAXD.  This should never happen, but the
 196        sufficiency of ENOUGH has not been proven exhaustively, hence the check.
 197        This assumes that when type == LENS, bits == 9.
 198
 199        sym increments through all symbols, and the loop terminates when
 200        all codes of length max, i.e. all codes, have been processed.  This
 201        routine permits incomplete codes, so another loop after this one fills
 202        in the rest of the decoding tables with invalid code markers.
 203      */
 204
 205     /* set up for code type */
 206     switch (type) {
 207     case CODES:
 208         base = extra = work;    /* dummy value--not used */
 209         match = 20;
 210         break;
 211     case LENS:
 212         base = lbase;
 213         extra = lext;
 214         match = 257;
 215         break;
 216     default:            /* DISTS */
 217         base = dbase;
 218         extra = dext;
 219         match = 0;
 220     }
 221
 222     /* initialize state for loop */
 223     huff = 0;                   /* starting code */
 224     sym = 0;                    /* starting code symbol */
 225     len = min;                  /* starting code length */
 226     next = *table;              /* current table to fill in */
 227     curr = root;                /* current table index bits */
 228     drop = 0;                   /* current bits to drop from code for index */
 229     low = (unsigned)(-1);       /* trigger new sub-table when len > root */
 230     used = 1U << root;          /* use root table entries */
 231     mask = used - 1;            /* mask for comparing low */
 232
 233     /* check available table space */
 234     if (type == LENS && used >= ENOUGH - MAXD)
 235         return 1;
 236
 237     /* process all codes and make table entries */
 238     for (;;) {
 239         /* create table entry */
 240         this.bits = (unsigned char)(len - drop);
 241         if (work[sym] + 1 < match) {
 242             this.op = (unsigned char)0;
 243             this.val = work[sym];
 244         }
 245         else if (work[sym] >= match) {
 246             this.op = (unsigned char)(extra[work[sym] - match]);
 247             this.val = base[work[sym] - match];
 248         }
 249         else {
 250             this.op = (unsigned char)(32 + 64);         /* end of block */
 251             this.val = 0;
 252         }
 253
 254         /* replicate for those indices with low len bits equal to huff */
 255         incr = 1U << (len - drop);
 256         fill = 1U << curr;
 257         min = fill;                 /* save offset to next table */
 258         do {
 259             fill -= incr;
 260             next[(huff >> drop) + fill] = this;
 261         } while (fill != 0);
 262
 263         /* backwards increment the len-bit code huff */
 264         incr = 1U << (len - 1);
 265         while (huff & incr)
 266             incr >>= 1;
 267         if (incr != 0) {
 268             huff &= incr - 1;
 269             huff += incr;
 270         }
 271         else
 272             huff = 0;
 273
 274         /* go to next symbol, update count, len */
 275         sym++;
 276         if (--(count[len]) == 0) {
 277             if (len == max) break;
 278             len = lens[work[sym]];
 279         }
 280
 281         /* create new sub-table if needed */
 282         if (len > root && (huff & mask) != low) {
 283             /* if first time, transition to sub-tables */
 284             if (drop == 0)
 285                 drop = root;
 286
 287             /* increment past last table */
 288             next += min;            /* here min is 1 << curr */
 289
 290             /* determine length of next table */
 291             curr = len - drop;
 292             left = (int)(1 << curr);
 293             while (curr + drop < max) {
 294                 left -= count[curr + drop];
 295                 if (left <= 0) break;
 296                 curr++;
 297                 left <<= 1;
 298             }
 299
 300             /* check for enough space */
 301             used += 1U << curr;
 302             if (type == LENS && used >= ENOUGH - MAXD)
 303                 return 1;
 304
 305             /* point entry in root table to sub-table */
 306             low = huff & mask;
 307             (*table)[low].op = (unsigned char)curr;
 308             (*table)[low].bits = (unsigned char)root;
 309             (*table)[low].val = (unsigned short)(next - *table);
 310         }
 311     }
 312
 313     /*
 314        Fill in rest of table for incomplete codes.  This loop is similar to the
 315        loop above in incrementing huff for table indices.  It is assumed that
 316        len is equal to curr + drop, so there is no loop needed to increment
 317        through high index bits.  When the current sub-table is filled, the loop
 318        drops back to the root table to fill in any remaining entries there.
 319      */
 320     this.op = (unsigned char)64;                /* invalid code marker */
 321     this.bits = (unsigned char)(len - drop);
 322     this.val = (unsigned short)0;
 323     while (huff != 0) {
 324         /* when done with sub-table, drop back to root table */
 325         if (drop != 0 && (huff & mask) != low) {
 326             drop = 0;
 327             len = root;
 328             next = *table;
 329             this.bits = (unsigned char)len;
 330         }
 331
 332         /* put invalid code marker in table */
 333         next[huff >> drop] = this;
 334
 335         /* backwards increment the len-bit code huff */
 336         incr = 1U << (len - 1);
 337         while (huff & incr)
 338             incr >>= 1;
 339         if (incr != 0) {
 340             huff &= incr - 1;
 341             huff += incr;
 342         }
 343         else
 344             huff = 0;
 345     }
 346
 347     /* set return parameters */
 348     *table += used;
 349     *bits = root;
 350     return 0;
 351 }