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/* inftrees.c -- generate Huffman trees for efficient decoding
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* Copyright (C) 1995-2003 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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const char inflate_copyright[] =
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" inflate 1.2.1 Copyright 1995-2003 Mark Adler ";
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If you use the zlib library in a product, an acknowledgment is welcome
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in the documentation of your product. If for some reason you cannot
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include such an acknowledgment, I would appreciate that you keep this
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copyright string in the executable of your product.
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Build a set of tables to decode the provided canonical Huffman code.
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The code lengths are lens[0..codes-1]. The result starts at *table,
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whose indices are 0..2^bits-1. work is a writable array of at least
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lens shorts, which is used as a work area. type is the type of code
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to be generated, CODES, LENS, or DISTS. On return, zero is success,
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-1 is an invalid code, and +1 means that ENOUGH isn't enough. table
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on return points to the next available entry's address. bits is the
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requested root table index bits, and on return it is the actual root
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table index bits. It will differ if the request is greater than the
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longest code or if it is less than the shortest code.
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int inflate_table(type, lens, codes, table, bits, work)
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unsigned short FAR *lens;
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code FAR * FAR *table;
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unsigned short FAR *work;
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unsigned len; /* a code's length in bits */
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unsigned sym; /* index of code symbols */
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unsigned min, max; /* minimum and maximum code lengths */
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unsigned root; /* number of index bits for root table */
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unsigned curr; /* number of index bits for current table */
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unsigned drop; /* code bits to drop for sub-table */
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int left; /* number of prefix codes available */
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unsigned used; /* code entries in table used */
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unsigned huff; /* Huffman code */
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unsigned incr; /* for incrementing code, index */
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unsigned fill; /* index for replicating entries */
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unsigned low; /* low bits for current root entry */
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unsigned mask; /* mask for low root bits */
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code this; /* table entry for duplication */
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code FAR *next; /* next available space in table */
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const unsigned short FAR *base; /* base value table to use */
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const unsigned short FAR *extra; /* extra bits table to use */
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int end; /* use base and extra for symbol > end */
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unsigned short count[MAXBITS+1]; /* number of codes of each length */
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unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
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static const unsigned short lbase[31] = { /* Length codes 257..285 base */
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3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
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35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
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static const unsigned short lext[31] = { /* Length codes 257..285 extra */
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16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
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19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 76, 66};
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static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
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1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
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257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
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8193, 12289, 16385, 24577, 0, 0};
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static const unsigned short dext[32] = { /* Distance codes 0..29 extra */
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16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22,
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23, 23, 24, 24, 25, 25, 26, 26, 27, 27,
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28, 28, 29, 29, 64, 64};
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Process a set of code lengths to create a canonical Huffman code. The
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code lengths are lens[0..codes-1]. Each length corresponds to the
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symbols 0..codes-1. The Huffman code is generated by first sorting the
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symbols by length from short to long, and retaining the symbol order
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for codes with equal lengths. Then the code starts with all zero bits
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for the first code of the shortest length, and the codes are integer
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increments for the same length, and zeros are appended as the length
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increases. For the deflate format, these bits are stored backwards
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from their more natural integer increment ordering, and so when the
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decoding tables are built in the large loop below, the integer codes
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are incremented backwards.
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This routine assumes, but does not check, that all of the entries in
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lens[] are in the range 0..MAXBITS. The caller must assure this.
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1..MAXBITS is interpreted as that code length. zero means that that
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symbol does not occur in this code.
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The codes are sorted by computing a count of codes for each length,
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creating from that a table of starting indices for each length in the
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sorted table, and then entering the symbols in order in the sorted
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table. The sorted table is work[], with that space being provided by
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The length counts are used for other purposes as well, i.e. finding
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the minimum and maximum length codes, determining if there are any
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codes at all, checking for a valid set of lengths, and looking ahead
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at length counts to determine sub-table sizes when building the
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/* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */
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for (len = 0; len <= MAXBITS; len++)
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for (sym = 0; sym < codes; sym++)
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/* bound code lengths, force root to be within code lengths */
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for (max = MAXBITS; max >= 1; max--)
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if (count[max] != 0) break;
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if (root > max) root = max;
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if (max == 0) return -1; /* no codes! */
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for (min = 1; min <= MAXBITS; min++)
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if (count[min] != 0) break;
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if (root < min) root = min;
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/* check for an over-subscribed or incomplete set of lengths */
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for (len = 1; len <= MAXBITS; len++) {
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if (left < 0) return -1; /* over-subscribed */
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if (left > 0 && (type == CODES || (codes - count[0] != 1)))
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return -1; /* incomplete set */
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/* generate offsets into symbol table for each length for sorting */
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for (len = 1; len < MAXBITS; len++)
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offs[len + 1] = offs[len] + count[len];
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/* sort symbols by length, by symbol order within each length */
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for (sym = 0; sym < codes; sym++)
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if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym;
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Create and fill in decoding tables. In this loop, the table being
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filled is at next and has curr index bits. The code being used is huff
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with length len. That code is converted to an index by dropping drop
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bits off of the bottom. For codes where len is less than drop + curr,
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those top drop + curr - len bits are incremented through all values to
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fill the table with replicated entries.
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root is the number of index bits for the root table. When len exceeds
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root, sub-tables are created pointed to by the root entry with an index
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of the low root bits of huff. This is saved in low to check for when a
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new sub-table should be started. drop is zero when the root table is
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being filled, and drop is root when sub-tables are being filled.
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When a new sub-table is needed, it is necessary to look ahead in the
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code lengths to determine what size sub-table is needed. The length
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counts are used for this, and so count[] is decremented as codes are
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entered in the tables.
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used keeps track of how many table entries have been allocated from the
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provided *table space. It is checked when a LENS table is being made
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against the space in *table, ENOUGH, minus the maximum space needed by
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the worst case distance code, MAXD. This should never happen, but the
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sufficiency of ENOUGH has not been proven exhaustively, hence the check.
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This assumes that when type == LENS, bits == 9.
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sym increments through all symbols, and the loop terminates when
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all codes of length max, i.e. all codes, have been processed. This
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routine permits incomplete codes, so another loop after this one fills
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in the rest of the decoding tables with invalid code markers.
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/* set up for code type */
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base = extra = work; /* dummy value--not used */
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/* initialize state for loop */
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huff = 0; /* starting code */
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sym = 0; /* starting code symbol */
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len = min; /* starting code length */
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next = *table; /* current table to fill in */
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curr = root; /* current table index bits */
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drop = 0; /* current bits to drop from code for index */
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low = (unsigned)(-1); /* trigger new sub-table when len > root */
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used = 1U << root; /* use root table entries */
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mask = used - 1; /* mask for comparing low */
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/* check available table space */
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if (type == LENS && used >= ENOUGH - MAXD)
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/* process all codes and make table entries */
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/* create table entry */
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this.bits = (unsigned char)(len - drop);
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if ((int)(work[sym]) < end) {
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this.op = (unsigned char)0;
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this.val = work[sym];
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else if ((int)(work[sym]) > end) {
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this.op = (unsigned char)(extra[work[sym]]);
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this.val = base[work[sym]];
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this.op = (unsigned char)(32 + 64); /* end of block */
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/* replicate for those indices with low len bits equal to huff */
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incr = 1U << (len - drop);
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next[(huff >> drop) + fill] = this;
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/* backwards increment the len-bit code huff */
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incr = 1U << (len - 1);
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/* go to next symbol, update count, len */
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if (--(count[len]) == 0) {
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if (len == max) break;
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len = lens[work[sym]];
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/* create new sub-table if needed */
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if (len > root && (huff & mask) != low) {
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/* if first time, transition to sub-tables */
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/* increment past last table */
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/* determine length of next table */
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left = (int)(1 << curr);
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while (curr + drop < max) {
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left -= count[curr + drop];
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if (left <= 0) break;
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/* check for enough space */
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if (type == LENS && used >= ENOUGH - MAXD)
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/* point entry in root table to sub-table */
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(*table)[low].op = (unsigned char)curr;
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(*table)[low].bits = (unsigned char)root;
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(*table)[low].val = (unsigned short)(next - *table);
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Fill in rest of table for incomplete codes. This loop is similar to the
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loop above in incrementing huff for table indices. It is assumed that
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len is equal to curr + drop, so there is no loop needed to increment
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through high index bits. When the current sub-table is filled, the loop
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drops back to the root table to fill in any remaining entries there.
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this.op = (unsigned char)64; /* invalid code marker */
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this.bits = (unsigned char)(len - drop);
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this.val = (unsigned short)0;
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/* when done with sub-table, drop back to root table */
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if (drop != 0 && (huff & mask) != low) {
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this.bits = (unsigned char)len;
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/* put invalid code marker in table */
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next[huff >> drop] = this;
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/* backwards increment the len-bit code huff */
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incr = 1U << (len - 1);
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/* set return parameters */
added
removed
zlib/inftrees.c
