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1 /* inftrees.h -- header to use inftrees.c
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2 * Copyright (C) 1995-2005, 2010 Mark Adler
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3 * For conditions of distribution and use, see copyright notice in zlib.h
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4 */
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5
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6 /* WARNING: this file should *not* be used by applications. It is
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7 part of the implementation of the compression library and is
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8 subject to change. Applications should only use zlib.h.
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9 */
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10
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11 /* Structure for decoding tables. Each entry provides either the
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12 information needed to do the operation requested by the code that
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13 indexed that table entry, or it provides a pointer to another
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14 table that indexes more bits of the code. op indicates whether
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15 the entry is a pointer to another table, a literal, a length or
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16 distance, an end-of-block, or an invalid code. For a table
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17 pointer, the low four bits of op is the number of index bits of
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18 that table. For a length or distance, the low four bits of op
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19 is the number of extra bits to get after the code. bits is
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20 the number of bits in this code or part of the code to drop off
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21 of the bit buffer. val is the actual byte to output in the case
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22 of a literal, the base length or distance, or the offset from
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23 the current table to the next table. Each entry is four bytes. */
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24 typedef struct {
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25 unsigned char op; /* operation, extra bits, table bits */
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26 unsigned char bits; /* bits in this part of the code */
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27 unsigned short val; /* offset in table or code value */
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28 } code;
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29
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30 /* op values as set by inflate_table():
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31 00000000 - literal
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32 0000tttt - table link, tttt != 0 is the number of table index bits
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33 0001eeee - length or distance, eeee is the number of extra bits
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34 01100000 - end of block
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35 01000000 - invalid code
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36 */
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37
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38 /* Maximum size of the dynamic table. The maximum number of code structures is
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39 1444, which is the sum of 852 for literal/length codes and 592 for distance
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40 codes. These values were found by exhaustive searches using the program
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41 examples/enough.c found in the zlib distribtution. The arguments to that
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42 program are the number of symbols, the initial root table size, and the
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43 maximum bit length of a code. "enough 286 9 15" for literal/length codes
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44 returns returns 852, and "enough 30 6 15" for distance codes returns 592.
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45 The initial root table size (9 or 6) is found in the fifth argument of the
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46 inflate_table() calls in inflate.c and infback.c. If the root table size is
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47 changed, then these maximum sizes would be need to be recalculated and
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48 updated. */
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49 #define ENOUGH_LENS 852
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50 #define ENOUGH_DISTS 592
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51 #define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS)
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52
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53 /* Type of code to build for inflate_table() */
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54 typedef enum {
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55 CODES,
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56 LENS,
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57 DISTS
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58 } codetype;
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59
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60 int ZLIB_INTERNAL inflate_table OF((codetype type, unsigned short FAR *lens,
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61 unsigned codes, code FAR * FAR *table,
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62 unsigned FAR *bits, unsigned short FAR *work));
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