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/* inftrees.c  generate Huffman trees for efficient decoding 
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* Copyright (C) 19952010 Mark Adler 
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* For conditions of distribution and use, see copyright notice in zlib.h 
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*/ 
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#include "zutil.h" 
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#include "inftrees.h" 
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#define MAXBITS 15 
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const char inflate_copyright[] = 
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" inflate 1.2.4 Copyright 19952010 Mark Adler "; 
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/* 
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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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*/ 
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/* 
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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..codes1]. The result starts at *table, 
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whose indices are 0..2^bits1. 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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*/ 
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int inflate_table(type, lens, codes, table, bits, work) 
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codetype type; 
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unsigned short FAR *lens; 
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unsigned codes; 
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code FAR * FAR *table; 
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unsigned FAR *bits; 
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unsigned short FAR *work; 
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{ 
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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 subtable */ 
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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 here; /* 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, 64, 195}; 
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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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/* 
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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..codes1]. Each length corresponds to the 
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symbols 0..codes1. 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 caller. 
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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 subtable sizes when building the 
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decoding tables. 
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*/ 
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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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count[len] = 0; 
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for (sym = 0; sym < codes; sym++) 
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count[lens[sym]]++; 
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/* bound code lengths, force root to be within code lengths */ 
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root = *bits; 
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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) { /* no symbols to code at all */ 
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here.op = (unsigned char)64; /* invalid code marker */ 
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here.bits = (unsigned char)1; 
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here.val = (unsigned short)0; 
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*(*table)++ = here; /* make a table to force an error */ 
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*(*table)++ = here; 
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*bits = 1; 
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return 0; /* no symbols, but wait for decoding to report error */ 
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} 
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for (min = 1; min < max; 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 oversubscribed or incomplete set of lengths */ 
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left = 1; 
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for (len = 1; len <= MAXBITS; len++) { 
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left <<= 1; 
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left = count[len]; 
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if (left < 0) return 1; /* oversubscribed */ 
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} 
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if (left > 0 && (type == CODES  max != 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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offs[1] = 0; 
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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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/* 
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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, subtables 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 subtable should be started. drop is zero when the root table is 
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being filled, and drop is root when subtables are being filled. 
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When a new subtable is needed, it is necessary to look ahead in the 
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code lengths to determine what size subtable 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 for LENS and DIST tables against 
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the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in 
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the initial root table size constants. See the comments in inftrees.h 
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for more information. 
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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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*/ 
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/* set up for code type */ 
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switch (type) { 
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case CODES: 
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base = extra = work; /* dummy valuenot used */ 
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end = 19; 
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break; 
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case LENS: 
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base = lbase; 
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base = 257; 
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extra = lext; 
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extra = 257; 
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end = 256; 
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break; 
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default: /* DISTS */ 
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base = dbase; 
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extra = dext; 
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end = 1; 
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} 
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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 subtable 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_LENS)  
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(type == DISTS && used >= ENOUGH_DISTS)) 
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return 1; 
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/* process all codes and make table entries */ 
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for (;;) { 
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/* create table entry */ 
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here.bits = (unsigned char)(len  drop); 
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if ((int)(work[sym]) < end) { 
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here.op = (unsigned char)0; 
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here.val = work[sym]; 
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} 
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else if ((int)(work[sym]) > end) { 
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here.op = (unsigned char)(extra[work[sym]]); 
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here.val = base[work[sym]]; 
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} 
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else { 
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here.op = (unsigned char)(32 + 64); /* end of block */ 
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here.val = 0; 
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} 
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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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fill = 1U << curr; 
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min = fill; /* save offset to next table */ 
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do { 
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fill = incr; 
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next[(huff >> drop) + fill] = here; 
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} while (fill != 0); 
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/* backwards increment the lenbit code huff */ 
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incr = 1U << (len  1); 
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while (huff & incr) 
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incr >>= 1; 
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if (incr != 0) { 
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huff &= incr  1; 
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huff += incr; 
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} 
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else 
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huff = 0; 
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/* go to next symbol, update count, len */ 
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sym++; 
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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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} 
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/* create new subtable if needed */ 
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if (len > root && (huff & mask) != low) { 
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/* if first time, transition to subtables */ 
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if (drop == 0) 
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drop = root; 
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/* increment past last table */ 
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next += min; /* here min is 1 << curr */ 
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/* determine length of next table */ 
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curr = len  drop; 
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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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curr++; 
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left <<= 1; 
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} 
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/* check for enough space */ 
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used += 1U << curr; 
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if ((type == LENS && used >= ENOUGH_LENS)  
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(type == DISTS && used >= ENOUGH_DISTS)) 
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return 1; 
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/* point entry in root table to subtable */ 
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low = huff & mask; 
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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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} 
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} 
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/* 
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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 subtable 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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*/ 
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here.op = (unsigned char)64; /* invalid code marker */ 
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here.bits = (unsigned char)(len  drop); 
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here.val = (unsigned short)0; 
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while (huff != 0) { 
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/* when done with subtable, drop back to root table */ 
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if (drop != 0 && (huff & mask) != low) { 
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drop = 0; 
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len = root; 
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next = *table; 
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here.bits = (unsigned char)len; 
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} 
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/* put invalid code marker in table */ 
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next[huff >> drop] = here; 
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/* backwards increment the lenbit code huff */ 
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incr = 1U << (len  1); 
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while (huff & incr) 
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incr >>= 1; 
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if (incr != 0) { 
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huff &= incr  1; 
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huff += incr; 
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} 
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else 
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huff = 0; 
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} 
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/* set return parameters */ 
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*table += used; 
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*bits = root; 
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return 0; 
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} 