1 /* inftrees.h -- header to use inftrees.c

2 * Copyright (C) 1995-2005, 2010 Mark Adler

3 * For conditions of distribution and use, see copyright notice in zlib.h

4 */

5

6 /* WARNING: this file should *not* be used by applications. It is

7 part of the implementation of the compression library and is

8 subject to change. Applications should only use zlib.h.

9 */

10

11 /* Structure for decoding tables. Each entry provides either the

12 information needed to do the operation requested by the code that

13 indexed that table entry, or it provides a pointer to another

14 table that indexes more bits of the code. op indicates whether

15 the entry is a pointer to another table, a literal, a length or

16 distance, an end-of-block, or an invalid code. For a table

17 pointer, the low four bits of op is the number of index bits of

18 that table. For a length or distance, the low four bits of op

19 is the number of extra bits to get after the code. bits is

20 the number of bits in this code or part of the code to drop off

21 of the bit buffer. val is the actual byte to output in the case

22 of a literal, the base length or distance, or the offset from

23 the current table to the next table. Each entry is four bytes. */

24 typedef struct {

25 unsigned char op; /* operation, extra bits, table bits */

26 unsigned char bits; /* bits in this part of the code */

27 unsigned short val; /* offset in table or code value */

28 } code;

29

30 /* op values as set by inflate_table():

31 00000000 - literal

32 0000tttt - table link, tttt != 0 is the number of table index bits

33 0001eeee - length or distance, eeee is the number of extra bits

34 01100000 - end of block

35 01000000 - invalid code

36 */

37

38 /* Maximum size of the dynamic table. The maximum number of code structures is

39 1444, which is the sum of 852 for literal/length codes and 592 for distance

40 codes. These values were found by exhaustive searches using the program

41 examples/enough.c found in the zlib distribtution. The arguments to that

42 program are the number of symbols, the initial root table size, and the

43 maximum bit length of a code. "enough 286 9 15" for literal/length codes

44 returns returns 852, and "enough 30 6 15" for distance codes returns 592.

45 The initial root table size (9 or 6) is found in the fifth argument of the

46 inflate_table() calls in inflate.c and infback.c. If the root table size is

47 changed, then these maximum sizes would be need to be recalculated and

48 updated. */

49 #define ENOUGH_LENS 852

50 #define ENOUGH_DISTS 592

51 #define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS)

52

53 /* Type of code to build for inflate_table() */

54 typedef enum {

55 CODES,

56 LENS,

57 DISTS

58 } codetype;

59

60 int ZLIB_INTERNAL inflate_table OF((codetype type, unsigned short FAR *lens,

61 unsigned codes, code FAR * FAR *table,

62 unsigned FAR *bits, unsigned short FAR *work));