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1.8.7

    1: /* inftrees.c -- generate Huffman trees for efficient decoding
    2:  * Copyright (C) 1995-2012 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 1.2.6 Copyright 1995-2012 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: 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, 203, 69};
   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:     for (len = 0; len <= MAXBITS; len++)
  108:         count[len] = 0;
  109:     for (sym = 0; sym < codes; sym++)
  110:         count[lens[sym]]++;
  111: 
  112:     /* bound code lengths, force root to be within code lengths */
  113:     root = *bits;
  114:     for (max = MAXBITS; max >= 1; max--)
  115:         if (count[max] != 0) break;
  116:     if (root > max) root = max;
  117:     if (max == 0) {                     /* no symbols to code at all */
  118:         here.op = (unsigned char)64;    /* invalid code marker */
  119:         here.bits = (unsigned char)1;
  120:         here.val = (unsigned short)0;
  121:         *(*table)++ = here;             /* make a table to force an error */
  122:         *(*table)++ = here;
  123:         *bits = 1;
  124:         return 0;     /* no symbols, but wait for decoding to report error */
  125:     }
  126:     for (min = 1; min < max; min++)
  127:         if (count[min] != 0) break;
  128:     if (root < min) root = min;
  129: 
  130:     /* check for an over-subscribed or incomplete set of lengths */
  131:     left = 1;
  132:     for (len = 1; len <= MAXBITS; len++) {
  133:         left <<= 1;
  134:         left -= count[len];
  135:         if (left < 0) return -1;        /* over-subscribed */
  136:     }
  137:     if (left > 0 && (type == CODES || max != 1))
  138:         return -1;                      /* incomplete set */
  139: 
  140:     /* generate offsets into symbol table for each length for sorting */
  141:     offs[1] = 0;
  142:     for (len = 1; len < MAXBITS; len++)
  143:         offs[len + 1] = offs[len] + count[len];
  144: 
  145:     /* sort symbols by length, by symbol order within each length */
  146:     for (sym = 0; sym < codes; sym++)
  147:         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:     switch (type) {
  182:     case CODES:
  183:         base = extra = work;    /* dummy value--not used */
  184:         end = 19;
  185:         break;
  186:     case LENS:
  187:         base = lbase;
  188:         base -= 257;
  189:         extra = lext;
  190:         extra -= 257;
  191:         end = 256;
  192:         break;
  193:     default:            /* DISTS */
  194:         base = dbase;
  195:         extra = dext;
  196:         end = -1;
  197:     }
  198: 
  199:     /* initialize state for loop */
  200:     huff = 0;                   /* starting code */
  201:     sym = 0;                    /* starting code symbol */
  202:     len = min;                  /* starting code length */
  203:     next = *table;              /* current table to fill in */
  204:     curr = root;                /* current table index bits */
  205:     drop = 0;                   /* current bits to drop from code for index */
  206:     low = (unsigned)(-1);       /* trigger new sub-table when len > root */
  207:     used = 1U << root;          /* use root table entries */
  208:     mask = used - 1;            /* mask for comparing low */
  209: 
  210:     /* check available table space */
  211:     if ((type == LENS && used >= ENOUGH_LENS) ||
  212:         (type == DISTS && used >= ENOUGH_DISTS))
  213:         return 1;
  214: 
  215:     /* process all codes and make table entries */
  216:     for (;;) {
  217:         /* create table entry */
  218:         here.bits = (unsigned char)(len - drop);
  219:         if ((int)(work[sym]) < end) {
  220:             here.op = (unsigned char)0;
  221:             here.val = work[sym];
  222:         }
  223:         else if ((int)(work[sym]) > end) {
  224:             here.op = (unsigned char)(extra[work[sym]]);
  225:             here.val = base[work[sym]];
  226:         }
  227:         else {
  228:             here.op = (unsigned char)(32 + 64);         /* end of block */
  229:             here.val = 0;
  230:         }
  231: 
  232:         /* replicate for those indices with low len bits equal to huff */
  233:         incr = 1U << (len - drop);
  234:         fill = 1U << curr;
  235:         min = fill;                 /* save offset to next table */
  236:         do {
  237:             fill -= incr;
  238:             next[(huff >> drop) + fill] = here;
  239:         } while (fill != 0);
  240: 
  241:         /* backwards increment the len-bit code huff */
  242:         incr = 1U << (len - 1);
  243:         while (huff & incr)
  244:             incr >>= 1;
  245:         if (incr != 0) {
  246:             huff &= incr - 1;
  247:             huff += incr;
  248:         }
  249:         else
  250:             huff = 0;
  251: 
  252:         /* go to next symbol, update count, len */
  253:         sym++;
  254:         if (--(count[len]) == 0) {
  255:             if (len == max) break;
  256:             len = lens[work[sym]];
  257:         }
  258: 
  259:         /* create new sub-table if needed */
  260:         if (len > root && (huff & mask) != low) {
  261:             /* if first time, transition to sub-tables */
  262:             if (drop == 0)
  263:                 drop = root;
  264: 
  265:             /* increment past last table */
  266:             next += min;            /* here min is 1 << curr */
  267: 
  268:             /* determine length of next table */
  269:             curr = len - drop;
  270:             left = (int)(1 << curr);
  271:             while (curr + drop < max) {
  272:                 left -= count[curr + drop];
  273:                 if (left <= 0) break;
  274:                 curr++;
  275:                 left <<= 1;
  276:             }
  277: 
  278:             /* check for enough space */
  279:             used += 1U << curr;
  280:             if ((type == LENS && used >= ENOUGH_LENS) ||
  281:                 (type == DISTS && used >= ENOUGH_DISTS))
  282:                 return 1;
  283: 
  284:             /* point entry in root table to sub-table */
  285:             low = huff & mask;
  286:             (*table)[low].op = (unsigned char)curr;
  287:             (*table)[low].bits = (unsigned char)root;
  288:             (*table)[low].val = (unsigned short)(next - *table);
  289:         }
  290:     }
  291: 
  292:     /* fill in remaining table entry if code is incomplete (guaranteed to have
  293:        at most one remaining entry, since if the code is incomplete, the
  294:        maximum code length that was allowed to get this far is one bit) */
  295:     if (huff != 0) {
  296:         here.op = (unsigned char)64;            /* invalid code marker */
  297:         here.bits = (unsigned char)(len - drop);
  298:         here.val = (unsigned short)0;
  299:         next[huff] = here;
  300:     }
  301: 
  302:     /* set return parameters */
  303:     *table += used;
  304:     *bits = root;
  305:     return 0;
  306: }