mirror of https://github.com/madler/zlib
63 lines
2.9 KiB
C
63 lines
2.9 KiB
C
/* inftrees.h -- header to use inftrees.c
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* Copyright (C) 1995-2005, 2010 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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/* WARNING: this file should *not* be used by applications. It is
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part of the implementation of the compression library and is
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subject to change. Applications should only use zlib.h.
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*/
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/* Structure for decoding tables. Each entry provides either the
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information needed to do the operation requested by the code that
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indexed that table entry, or it provides a pointer to another
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table that indexes more bits of the code. op indicates whether
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the entry is a pointer to another table, a literal, a length or
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distance, an end-of-block, or an invalid code. For a table
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pointer, the low four bits of op is the number of index bits of
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that table. For a length or distance, the low four bits of op
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is the number of extra bits to get after the code. bits is
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the number of bits in this code or part of the code to drop off
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of the bit buffer. val is the actual byte to output in the case
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of a literal, the base length or distance, or the offset from
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the current table to the next table. Each entry is four bytes. */
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typedef struct {
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unsigned char op; /* operation, extra bits, table bits */
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unsigned char bits; /* bits in this part of the code */
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unsigned short val; /* offset in table or code value */
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} code;
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/* op values as set by inflate_table():
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00000000 - literal
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0000tttt - table link, tttt != 0 is the number of table index bits
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0001eeee - length or distance, eeee is the number of extra bits
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01100000 - end of block
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01000000 - invalid code
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*/
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/* Maximum size of the dynamic table. The maximum number of code structures is
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1444, which is the sum of 852 for literal/length codes and 592 for distance
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codes. These values were found by exhaustive searches using the program
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examples/enough.c found in the zlib distribution. The arguments to that
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program are the number of symbols, the initial root table size, and the
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maximum bit length of a code. "enough 286 9 15" for literal/length codes
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returns returns 852, and "enough 30 6 15" for distance codes returns 592.
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The initial root table size (9 or 6) is found in the fifth argument of the
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inflate_table() calls in inflate.c and infback.c. If the root table size is
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changed, then these maximum sizes would be need to be recalculated and
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updated. */
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#define ENOUGH_LENS 852
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#define ENOUGH_DISTS 592
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#define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS)
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/* Type of code to build for inflate_table() */
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typedef enum {
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CODES,
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LENS,
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DISTS
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} codetype;
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int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens,
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unsigned codes, code FAR * FAR *table,
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unsigned FAR *bits, unsigned short FAR *work);
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