+/* inftrees.c -- generate Huffman trees for efficient decoding
+ * Copyright (C) 1995-2013 Mark Adler
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ */
+
+#include "zutil.h"
+#include "inftrees.h"
+
+#define MAXBITS 15
+
+const char inflate_copyright[] =
+ " inflate 1.2.8 Copyright 1995-2013 Mark Adler ";
+/*
+ If you use the zlib library in a product, an acknowledgment is welcome
+ in the documentation of your product. If for some reason you cannot
+ include such an acknowledgment, I would appreciate that you keep this
+ copyright string in the executable of your product.
+ */
+
+/*
+ Build a set of tables to decode the provided canonical Huffman code.
+ The code lengths are lens[0..codes-1]. The result starts at *table,
+ whose indices are 0..2^bits-1. work is a writable array of at least
+ lens shorts, which is used as a work area. type is the type of code
+ to be generated, CODES, LENS, or DISTS. On return, zero is success,
+ -1 is an invalid code, and +1 means that ENOUGH isn't enough. table
+ on return points to the next available entry's address. bits is the
+ requested root table index bits, and on return it is the actual root
+ table index bits. It will differ if the request is greater than the
+ longest code or if it is less than the shortest code.
+ */
+int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens,
+ unsigned codes, code FAR * FAR *table,
+ unsigned FAR *bits, unsigned short FAR *work)
+{
+ unsigned len; /* a code's length in bits */
+ unsigned sym; /* index of code symbols */
+ unsigned min, max; /* minimum and maximum code lengths */
+ unsigned root; /* number of index bits for root table */
+ unsigned curr; /* number of index bits for current table */
+ unsigned drop; /* code bits to drop for sub-table */
+ int left; /* number of prefix codes available */
+ unsigned used; /* code entries in table used */
+ unsigned huff; /* Huffman code */
+ unsigned incr; /* for incrementing code, index */
+ unsigned fill; /* index for replicating entries */
+ unsigned low; /* low bits for current root entry */
+ unsigned mask; /* mask for low root bits */
+ code here; /* table entry for duplication */
+ code FAR *next; /* next available space in table */
+ const unsigned short FAR *base; /* base value table to use */
+ const unsigned short FAR *extra; /* extra bits table to use */
+ int end; /* use base and extra for symbol > end */
+ unsigned short count[MAXBITS+1]; /* number of codes of each length */
+ unsigned short offs[MAXBITS+1]; /* offsets in table for each length */
+ static const unsigned short lbase[31] = { /* Length codes 257..285 base */
+ 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
+ 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258, 0, 0};
+ static const unsigned short lext[31] = { /* Length codes 257..285 extra */
+ 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18,
+ 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 16, 72, 78};
+ static const unsigned short dbase[32] = { /* Distance codes 0..29 base */
+ 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
+ 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
+ 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 */
+ here.op = (unsigned char)64; /* invalid code marker */
+ here.bits = (unsigned char)1;
+ here.val = (unsigned short)0;
+ *(*table)++ = here; /* make a table to force an error */
+ *(*table)++ = here;
+ *bits = 1;
+ return 0; /* no symbols, but wait for decoding to report error */
+ }
+ for (min = 1; min < max; 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 for LENS and DIST tables against
+ the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in
+ the initial root table size constants. See the comments in inftrees.h
+ for more information.
+
+ 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;
+ }
+
+ /* initialize state for loop */
+ huff = 0; /* starting code */
+ sym = 0; /* starting code symbol */
+ len = min; /* starting code length */
+ next = *table; /* current table to fill in */
+ curr = root; /* current table index bits */
+ drop = 0; /* current bits to drop from code for index */
+ low = (unsigned)(-1); /* trigger new sub-table when len > root */
+ used = 1U << root; /* use root table entries */
+ mask = used - 1; /* mask for comparing low */
+
+ /* check available table space */
+ if ((type == LENS && used > ENOUGH_LENS) ||
+ (type == DISTS && used > ENOUGH_DISTS))
+ return 1;
+
+ /* process all codes and make table entries */
+ for (;;) {
+ /* create table entry */
+ here.bits = (unsigned char)(len - drop);
+ if ((int)(work[sym]) < end) {
+ here.op = (unsigned char)0;
+ here.val = work[sym];
+ }
+ else if ((int)(work[sym]) > end) {
+ here.op = (unsigned char)(extra[work[sym]]);
+ here.val = base[work[sym]];
+ }
+ else {
+ here.op = (unsigned char)(32 + 64); /* end of block */
+ here.val = 0;
+ }
+
+ /* replicate for those indices with low len bits equal to huff */
+ incr = 1U << (len - drop);
+ fill = 1U << curr;
+ min = fill; /* save offset to next table */
+ do {
+ fill -= incr;
+ next[(huff >> drop) + fill] = here;
+ } while (fill != 0);
+
+ /* backwards increment the len-bit code huff */
+ incr = 1U << (len - 1);
+ while (huff & incr)
+ incr >>= 1;
+ if (incr != 0) {
+ huff &= incr - 1;
+ huff += incr;
+ }
+ else
+ huff = 0;
+
+ /* go to next symbol, update count, len */
+ sym++;
+ if (--(count[len]) == 0) {
+ if (len == max) break;
+ len = lens[work[sym]];
+ }
+
+ /* create new sub-table if needed */
+ if (len > root && (huff & mask) != low) {
+ /* if first time, transition to sub-tables */
+ if (drop == 0)
+ drop = root;
+
+ /* increment past last table */
+ next += min; /* here min is 1 << curr */
+
+ /* determine length of next table */
+ curr = len - drop;
+ left = (int)(1 << curr);
+ while (curr + drop < max) {
+ left -= count[curr + drop];
+ if (left <= 0) break;
+ curr++;
+ left <<= 1;
+ }
+
+ /* check for enough space */
+ used += 1U << curr;
+ if ((type == LENS && used > ENOUGH_LENS) ||
+ (type == DISTS && used > ENOUGH_DISTS))
+ return 1;
+
+ /* point entry in root table to sub-table */
+ low = huff & mask;
+ (*table)[low].op = (unsigned char)curr;
+ (*table)[low].bits = (unsigned char)root;
+ (*table)[low].val = (unsigned short)(next - *table);
+ }
+ }
+
+ /* fill in remaining table entry if code is incomplete (guaranteed to have
+ at most one remaining entry, since if the code is incomplete, the
+ maximum code length that was allowed to get this far is one bit) */
+ if (huff != 0) {
+ here.op = (unsigned char)64; /* invalid code marker */
+ here.bits = (unsigned char)(len - drop);
+ here.val = (unsigned short)0;
+ next[huff] = here;
+ }
+
+ /* set return parameters */
+ *table += used;
+ *bits = root;
+ return 0;
+}
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