alpar@9: /* inftrees.c -- generate Huffman trees for efficient decoding
alpar@9:  * Copyright (C) 1995-2010 Mark Adler
alpar@9:  * For conditions of distribution and use, see copyright notice in zlib.h
alpar@9:  */
alpar@9: 
alpar@9: #include "zutil.h"
alpar@9: #include "inftrees.h"
alpar@9: 
alpar@9: #define MAXBITS 15
alpar@9: 
alpar@9: const char inflate_copyright[] =
alpar@9:    " inflate 1.2.5 Copyright 1995-2010 Mark Adler ";
alpar@9: /*
alpar@9:   If you use the zlib library in a product, an acknowledgment is welcome
alpar@9:   in the documentation of your product. If for some reason you cannot
alpar@9:   include such an acknowledgment, I would appreciate that you keep this
alpar@9:   copyright string in the executable of your product.
alpar@9:  */
alpar@9: 
alpar@9: /*
alpar@9:    Build a set of tables to decode the provided canonical Huffman code.
alpar@9:    The code lengths are lens[0..codes-1].  The result starts at *table,
alpar@9:    whose indices are 0..2^bits-1.  work is a writable array of at least
alpar@9:    lens shorts, which is used as a work area.  type is the type of code
alpar@9:    to be generated, CODES, LENS, or DISTS.  On return, zero is success,
alpar@9:    -1 is an invalid code, and +1 means that ENOUGH isn't enough.  table
alpar@9:    on return points to the next available entry's address.  bits is the
alpar@9:    requested root table index bits, and on return it is the actual root
alpar@9:    table index bits.  It will differ if the request is greater than the
alpar@9:    longest code or if it is less than the shortest code.
alpar@9:  */
alpar@9: int ZLIB_INTERNAL inflate_table(type, lens, codes, table, bits, work)
alpar@9: codetype type;
alpar@9: unsigned short FAR *lens;
alpar@9: unsigned codes;
alpar@9: code FAR * FAR *table;
alpar@9: unsigned FAR *bits;
alpar@9: unsigned short FAR *work;
alpar@9: {
alpar@9:     unsigned len;               /* a code's length in bits */
alpar@9:     unsigned sym;               /* index of code symbols */
alpar@9:     unsigned min, max;          /* minimum and maximum code lengths */
alpar@9:     unsigned root;              /* number of index bits for root table */
alpar@9:     unsigned curr;              /* number of index bits for current table */
alpar@9:     unsigned drop;              /* code bits to drop for sub-table */
alpar@9:     int left;                   /* number of prefix codes available */
alpar@9:     unsigned used;              /* code entries in table used */
alpar@9:     unsigned huff;              /* Huffman code */
alpar@9:     unsigned incr;              /* for incrementing code, index */
alpar@9:     unsigned fill;              /* index for replicating entries */
alpar@9:     unsigned low;               /* low bits for current root entry */
alpar@9:     unsigned mask;              /* mask for low root bits */
alpar@9:     code here;                  /* table entry for duplication */
alpar@9:     code FAR *next;             /* next available space in table */
alpar@9:     const unsigned short FAR *base;     /* base value table to use */
alpar@9:     const unsigned short FAR *extra;    /* extra bits table to use */
alpar@9:     int end;                    /* use base and extra for symbol > end */
alpar@9:     unsigned short count[MAXBITS+1];    /* number of codes of each length */
alpar@9:     unsigned short offs[MAXBITS+1];     /* offsets in table for each length */
alpar@9:     static const unsigned short lbase[31] = { /* Length codes 257..285 base */
alpar@9:         3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
alpar@9:         35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
alpar@9:     static const unsigned short lext[31] = { /* Length codes 257..285 extra */
alpar@9:         16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
alpar@9:         19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 73, 195};
alpar@9:     static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
alpar@9:         1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
alpar@9:         257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
alpar@9:         8193, 12289, 16385, 24577, 0, 0};
alpar@9:     static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
alpar@9:         16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
alpar@9:         23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
alpar@9:         28, 28, 29, 29, 64, 64};
alpar@9: 
alpar@9:     /*
alpar@9:        Process a set of code lengths to create a canonical Huffman code.  The
alpar@9:        code lengths are lens[0..codes-1].  Each length corresponds to the
alpar@9:        symbols 0..codes-1.  The Huffman code is generated by first sorting the
alpar@9:        symbols by length from short to long, and retaining the symbol order
alpar@9:        for codes with equal lengths.  Then the code starts with all zero bits
alpar@9:        for the first code of the shortest length, and the codes are integer
alpar@9:        increments for the same length, and zeros are appended as the length
alpar@9:        increases.  For the deflate format, these bits are stored backwards
alpar@9:        from their more natural integer increment ordering, and so when the
alpar@9:        decoding tables are built in the large loop below, the integer codes
alpar@9:        are incremented backwards.
alpar@9: 
alpar@9:        This routine assumes, but does not check, that all of the entries in
alpar@9:        lens[] are in the range 0..MAXBITS.  The caller must assure this.
alpar@9:        1..MAXBITS is interpreted as that code length.  zero means that that
alpar@9:        symbol does not occur in this code.
alpar@9: 
alpar@9:        The codes are sorted by computing a count of codes for each length,
alpar@9:        creating from that a table of starting indices for each length in the
alpar@9:        sorted table, and then entering the symbols in order in the sorted
alpar@9:        table.  The sorted table is work[], with that space being provided by
alpar@9:        the caller.
alpar@9: 
alpar@9:        The length counts are used for other purposes as well, i.e. finding
alpar@9:        the minimum and maximum length codes, determining if there are any
alpar@9:        codes at all, checking for a valid set of lengths, and looking ahead
alpar@9:        at length counts to determine sub-table sizes when building the
alpar@9:        decoding tables.
alpar@9:      */
alpar@9: 
alpar@9:     /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
alpar@9:     for (len = 0; len <= MAXBITS; len++)
alpar@9:         count[len] = 0;
alpar@9:     for (sym = 0; sym < codes; sym++)
alpar@9:         count[lens[sym]]++;
alpar@9: 
alpar@9:     /* bound code lengths, force root to be within code lengths */
alpar@9:     root = *bits;
alpar@9:     for (max = MAXBITS; max >= 1; max--)
alpar@9:         if (count[max] != 0) break;
alpar@9:     if (root > max) root = max;
alpar@9:     if (max == 0) {                     /* no symbols to code at all */
alpar@9:         here.op = (unsigned char)64;    /* invalid code marker */
alpar@9:         here.bits = (unsigned char)1;
alpar@9:         here.val = (unsigned short)0;
alpar@9:         *(*table)++ = here;             /* make a table to force an error */
alpar@9:         *(*table)++ = here;
alpar@9:         *bits = 1;
alpar@9:         return 0;     /* no symbols, but wait for decoding to report error */
alpar@9:     }
alpar@9:     for (min = 1; min < max; min++)
alpar@9:         if (count[min] != 0) break;
alpar@9:     if (root < min) root = min;
alpar@9: 
alpar@9:     /* check for an over-subscribed or incomplete set of lengths */
alpar@9:     left = 1;
alpar@9:     for (len = 1; len <= MAXBITS; len++) {
alpar@9:         left <<= 1;
alpar@9:         left -= count[len];
alpar@9:         if (left < 0) return -1;        /* over-subscribed */
alpar@9:     }
alpar@9:     if (left > 0 && (type == CODES || max != 1))
alpar@9:         return -1;                      /* incomplete set */
alpar@9: 
alpar@9:     /* generate offsets into symbol table for each length for sorting */
alpar@9:     offs[1] = 0;
alpar@9:     for (len = 1; len < MAXBITS; len++)
alpar@9:         offs[len + 1] = offs[len] + count[len];
alpar@9: 
alpar@9:     /* sort symbols by length, by symbol order within each length */
alpar@9:     for (sym = 0; sym < codes; sym++)
alpar@9:         if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
alpar@9: 
alpar@9:     /*
alpar@9:        Create and fill in decoding tables.  In this loop, the table being
alpar@9:        filled is at next and has curr index bits.  The code being used is huff
alpar@9:        with length len.  That code is converted to an index by dropping drop
alpar@9:        bits off of the bottom.  For codes where len is less than drop + curr,
alpar@9:        those top drop + curr - len bits are incremented through all values to
alpar@9:        fill the table with replicated entries.
alpar@9: 
alpar@9:        root is the number of index bits for the root table.  When len exceeds
alpar@9:        root, sub-tables are created pointed to by the root entry with an index
alpar@9:        of the low root bits of huff.  This is saved in low to check for when a
alpar@9:        new sub-table should be started.  drop is zero when the root table is
alpar@9:        being filled, and drop is root when sub-tables are being filled.
alpar@9: 
alpar@9:        When a new sub-table is needed, it is necessary to look ahead in the
alpar@9:        code lengths to determine what size sub-table is needed.  The length
alpar@9:        counts are used for this, and so count[] is decremented as codes are
alpar@9:        entered in the tables.
alpar@9: 
alpar@9:        used keeps track of how many table entries have been allocated from the
alpar@9:        provided *table space.  It is checked for LENS and DIST tables against
alpar@9:        the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
alpar@9:        the initial root table size constants.  See the comments in inftrees.h
alpar@9:        for more information.
alpar@9: 
alpar@9:        sym increments through all symbols, and the loop terminates when
alpar@9:        all codes of length max, i.e. all codes, have been processed.  This
alpar@9:        routine permits incomplete codes, so another loop after this one fills
alpar@9:        in the rest of the decoding tables with invalid code markers.
alpar@9:      */
alpar@9: 
alpar@9:     /* set up for code type */
alpar@9:     switch (type) {
alpar@9:     case CODES:
alpar@9:         base = extra = work;    /* dummy value--not used */
alpar@9:         end = 19;
alpar@9:         break;
alpar@9:     case LENS:
alpar@9:         base = lbase;
alpar@9:         base -= 257;
alpar@9:         extra = lext;
alpar@9:         extra -= 257;
alpar@9:         end = 256;
alpar@9:         break;
alpar@9:     default:            /* DISTS */
alpar@9:         base = dbase;
alpar@9:         extra = dext;
alpar@9:         end = -1;
alpar@9:     }
alpar@9: 
alpar@9:     /* initialize state for loop */
alpar@9:     huff = 0;                   /* starting code */
alpar@9:     sym = 0;                    /* starting code symbol */
alpar@9:     len = min;                  /* starting code length */
alpar@9:     next = *table;              /* current table to fill in */
alpar@9:     curr = root;                /* current table index bits */
alpar@9:     drop = 0;                   /* current bits to drop from code for index */
alpar@9:     low = (unsigned)(-1);       /* trigger new sub-table when len > root */
alpar@9:     used = 1U << root;          /* use root table entries */
alpar@9:     mask = used - 1;            /* mask for comparing low */
alpar@9: 
alpar@9:     /* check available table space */
alpar@9:     if ((type == LENS && used >= ENOUGH_LENS) ||
alpar@9:         (type == DISTS && used >= ENOUGH_DISTS))
alpar@9:         return 1;
alpar@9: 
alpar@9:     /* process all codes and make table entries */
alpar@9:     for (;;) {
alpar@9:         /* create table entry */
alpar@9:         here.bits = (unsigned char)(len - drop);
alpar@9:         if ((int)(work[sym]) < end) {
alpar@9:             here.op = (unsigned char)0;
alpar@9:             here.val = work[sym];
alpar@9:         }
alpar@9:         else if ((int)(work[sym]) > end) {
alpar@9:             here.op = (unsigned char)(extra[work[sym]]);
alpar@9:             here.val = base[work[sym]];
alpar@9:         }
alpar@9:         else {
alpar@9:             here.op = (unsigned char)(32 + 64);         /* end of block */
alpar@9:             here.val = 0;
alpar@9:         }
alpar@9: 
alpar@9:         /* replicate for those indices with low len bits equal to huff */
alpar@9:         incr = 1U << (len - drop);
alpar@9:         fill = 1U << curr;
alpar@9:         min = fill;                 /* save offset to next table */
alpar@9:         do {
alpar@9:             fill -= incr;
alpar@9:             next[(huff >> drop) + fill] = here;
alpar@9:         } while (fill != 0);
alpar@9: 
alpar@9:         /* backwards increment the len-bit code huff */
alpar@9:         incr = 1U << (len - 1);
alpar@9:         while (huff & incr)
alpar@9:             incr >>= 1;
alpar@9:         if (incr != 0) {
alpar@9:             huff &= incr - 1;
alpar@9:             huff += incr;
alpar@9:         }
alpar@9:         else
alpar@9:             huff = 0;
alpar@9: 
alpar@9:         /* go to next symbol, update count, len */
alpar@9:         sym++;
alpar@9:         if (--(count[len]) == 0) {
alpar@9:             if (len == max) break;
alpar@9:             len = lens[work[sym]];
alpar@9:         }
alpar@9: 
alpar@9:         /* create new sub-table if needed */
alpar@9:         if (len > root && (huff & mask) != low) {
alpar@9:             /* if first time, transition to sub-tables */
alpar@9:             if (drop == 0)
alpar@9:                 drop = root;
alpar@9: 
alpar@9:             /* increment past last table */
alpar@9:             next += min;            /* here min is 1 << curr */
alpar@9: 
alpar@9:             /* determine length of next table */
alpar@9:             curr = len - drop;
alpar@9:             left = (int)(1 << curr);
alpar@9:             while (curr + drop < max) {
alpar@9:                 left -= count[curr + drop];
alpar@9:                 if (left <= 0) break;
alpar@9:                 curr++;
alpar@9:                 left <<= 1;
alpar@9:             }
alpar@9: 
alpar@9:             /* check for enough space */
alpar@9:             used += 1U << curr;
alpar@9:             if ((type == LENS && used >= ENOUGH_LENS) ||
alpar@9:                 (type == DISTS && used >= ENOUGH_DISTS))
alpar@9:                 return 1;
alpar@9: 
alpar@9:             /* point entry in root table to sub-table */
alpar@9:             low = huff & mask;
alpar@9:             (*table)[low].op = (unsigned char)curr;
alpar@9:             (*table)[low].bits = (unsigned char)root;
alpar@9:             (*table)[low].val = (unsigned short)(next - *table);
alpar@9:         }
alpar@9:     }
alpar@9: 
alpar@9:     /*
alpar@9:        Fill in rest of table for incomplete codes.  This loop is similar to the
alpar@9:        loop above in incrementing huff for table indices.  It is assumed that
alpar@9:        len is equal to curr + drop, so there is no loop needed to increment
alpar@9:        through high index bits.  When the current sub-table is filled, the loop
alpar@9:        drops back to the root table to fill in any remaining entries there.
alpar@9:      */
alpar@9:     here.op = (unsigned char)64;                /* invalid code marker */
alpar@9:     here.bits = (unsigned char)(len - drop);
alpar@9:     here.val = (unsigned short)0;
alpar@9:     while (huff != 0) {
alpar@9:         /* when done with sub-table, drop back to root table */
alpar@9:         if (drop != 0 && (huff & mask) != low) {
alpar@9:             drop = 0;
alpar@9:             len = root;
alpar@9:             next = *table;
alpar@9:             here.bits = (unsigned char)len;
alpar@9:         }
alpar@9: 
alpar@9:         /* put invalid code marker in table */
alpar@9:         next[huff >> drop] = here;
alpar@9: 
alpar@9:         /* backwards increment the len-bit code huff */
alpar@9:         incr = 1U << (len - 1);
alpar@9:         while (huff & incr)
alpar@9:             incr >>= 1;
alpar@9:         if (incr != 0) {
alpar@9:             huff &= incr - 1;
alpar@9:             huff += incr;
alpar@9:         }
alpar@9:         else
alpar@9:             huff = 0;
alpar@9:     }
alpar@9: 
alpar@9:     /* set return parameters */
alpar@9:     *table += used;
alpar@9:     *bits = root;
alpar@9:     return 0;
alpar@9: }