- 8193, 12289, 16385, 24577, 0, 0};
- static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
- 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
- 23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
- 28, 28, 29, 29, 64, 64};
-
- /*
- Process a set of code lengths to create a canonical Huffman code. The
- code lengths are lens[0..codes-1]. Each length corresponds to the
- symbols 0..codes-1. The Huffman code is generated by first sorting the
- symbols by length from short to long, and retaining the symbol order
- for codes with equal lengths. Then the code starts with all zero bits
- for the first code of the shortest length, and the codes are integer
- increments for the same length, and zeros are appended as the length
- increases. For the deflate format, these bits are stored backwards
- from their more natural integer increment ordering, and so when the
- decoding tables are built in the large loop below, the integer codes
- are incremented backwards.
-
- This routine assumes, but does not check, that all of the entries in
- lens[] are in the range 0..MAXBITS. The caller must assure this.
- 1..MAXBITS is interpreted as that code length. zero means that that
- symbol does not occur in this code.
-
- The codes are sorted by computing a count of codes for each length,
- creating from that a table of starting indices for each length in the
- sorted table, and then entering the symbols in order in the sorted
- table. The sorted table is work[], with that space being provided by
- the caller.
-
- The length counts are used for other purposes as well, i.e. finding
- the minimum and maximum length codes, determining if there are any
- codes at all, checking for a valid set of lengths, and looking ahead
- at length counts to determine sub-table sizes when building the
- decoding tables.
- */
-
- /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
- for (len = 0; len <= MAXBITS; len++)
- count[len] = 0;
- for (sym = 0; sym < codes; sym++)
- count[lens[sym]]++;
-
- /* bound code lengths, force root to be within code lengths */
- root = *bits;
- for (max = MAXBITS; max >= 1; max--)
- if (count[max] != 0) break;
- if (root > max) root = max;
- if (max == 0) { /* no symbols to code at all */
- this.op = (unsigned char)64; /* invalid code marker */
- this.bits = (unsigned char)1;
- this.val = (unsigned short)0;
- *(*table)++ = this; /* make a table to force an error */
- *(*table)++ = this;
- *bits = 1;
- return 0; /* no symbols, but wait for decoding to report error */
- }
- for (min = 1; min <= MAXBITS; min++)
- if (count[min] != 0) break;
- if (root < min) root = min;
-
- /* check for an over-subscribed or incomplete set of lengths */
- left = 1;
- for (len = 1; len <= MAXBITS; len++) {
- left <<= 1;
- left -= count[len];
- if (left < 0) return -1; /* over-subscribed */
- }
- if (left > 0 && (type == CODES || max != 1))
- return -1; /* incomplete set */
-
- /* generate offsets into symbol table for each length for sorting */
- offs[1] = 0;
- for (len = 1; len < MAXBITS; len++)
- offs[len + 1] = offs[len] + count[len];
-
- /* sort symbols by length, by symbol order within each length */
- for (sym = 0; sym < codes; sym++)
- if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
-
- /*
- Create and fill in decoding tables. In this loop, the table being
- filled is at next and has curr index bits. The code being used is huff
- with length len. That code is converted to an index by dropping drop
- bits off of the bottom. For codes where len is less than drop + curr,
- those top drop + curr - len bits are incremented through all values to
- fill the table with replicated entries.
-
- root is the number of index bits for the root table. When len exceeds
- root, sub-tables are created pointed to by the root entry with an index
- of the low root bits of huff. This is saved in low to check for when a
- new sub-table should be started. drop is zero when the root table is
- being filled, and drop is root when sub-tables are being filled.
-
- When a new sub-table is needed, it is necessary to look ahead in the
- code lengths to determine what size sub-table is needed. The length
- counts are used for this, and so count[] is decremented as codes are
- entered in the tables.
-
- used keeps track of how many table entries have been allocated from the
- provided *table space. It is checked when a LENS table is being made
- against the space in *table, ENOUGH, minus the maximum space needed by
- the worst case distance code, MAXD. This should never happen, but the
- sufficiency of ENOUGH has not been proven exhaustively, hence the check.
- This assumes that when type == LENS, bits == 9.
-
- sym increments through all symbols, and the loop terminates when
- all codes of length max, i.e. all codes, have been processed. This
- routine permits incomplete codes, so another loop after this one fills
- in the rest of the decoding tables with invalid code markers.
- */
-
- /* set up for code type */
- switch (type) {
- case CODES:
- base = extra = work; /* dummy value--not used */
- end = 19;
- break;
- case LENS:
- base = lbase;
- base -= 257;
- extra = lext;
- extra -= 257;
- end = 256;
- break;
- default: /* DISTS */
- base = dbase;
- extra = dext;
- end = -1;
- }