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4349 | Serge | 1 | /* inftrees.h -- header to use inftrees.c |
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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 | |||
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)); |