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-/* inftrees.c -- generate Huffman trees for efficient decoding
- * Copyright (C) 1995-2005 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 1.2.3 Copyright 1995-2005 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 inflate_table(type, lens, codes, table, bits, work)
-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 this; /* 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, 201, 196};
- 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 */
- 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;
- }
-
- /* 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 - MAXD)
- return 1;
-
- /* process all codes and make table entries */
- for (;;) {
- /* create table entry */
- this.bits = (unsigned char)(len - drop);
- if ((int)(work[sym]) < end) {
- this.op = (unsigned char)0;
- this.val = work[sym];
- }
- else if ((int)(work[sym]) > end) {
- this.op = (unsigned char)(extra[work[sym]]);
- this.val = base[work[sym]];
- }
- else {
- this.op = (unsigned char)(32 + 64); /* end of block */
- this.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] = this;
- } 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 - MAXD)
- 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 rest of table for incomplete codes. This loop is similar to the
- loop above in incrementing huff for table indices. It is assumed that
- len is equal to curr + drop, so there is no loop needed to increment
- through high index bits. When the current sub-table is filled, the loop
- drops back to the root table to fill in any remaining entries there.
- */
- this.op = (unsigned char)64; /* invalid code marker */
- this.bits = (unsigned char)(len - drop);
- this.val = (unsigned short)0;
- while (huff != 0) {
- /* when done with sub-table, drop back to root table */
- if (drop != 0 && (huff & mask) != low) {
- drop = 0;
- len = root;
- next = *table;
- this.bits = (unsigned char)len;
- }
-
- /* put invalid code marker in table */
- next[huff >> drop] = this;
-
- /* 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;
- }
-
- /* set return parameters */
- *table += used;
- *bits = root;
- return 0;
-}