inftrees.h (2993B)
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 #ifndef INFTREES_H 7 #define INFTREES_H 8 9 /* WARNING: this file should *not* be used by applications. It is 10 part of the implementation of the compression library and is 11 subject to change. Applications should only use zlib.h. 12 */ 13 14 /* Structure for decoding tables. Each entry provides either the 15 information needed to do the operation requested by the code that 16 indexed that table entry, or it provides a pointer to another 17 table that indexes more bits of the code. op indicates whether 18 the entry is a pointer to another table, a literal, a length or 19 distance, an end-of-block, or an invalid code. For a table 20 pointer, the low four bits of op is the number of index bits of 21 that table. For a length or distance, the low four bits of op 22 is the number of extra bits to get after the code. bits is 23 the number of bits in this code or part of the code to drop off 24 of the bit buffer. val is the actual byte to output in the case 25 of a literal, the base length or distance, or the offset from 26 the current table to the next table. Each entry is four bytes. */ 27 typedef struct { 28 unsigned char op; /* operation, extra bits, table bits */ 29 unsigned char bits; /* bits in this part of the code */ 30 unsigned short val; /* offset in table or code value */ 31 } code; 32 33 /* op values as set by inflate_table(): 34 00000000 - literal 35 0000tttt - table link, tttt != 0 is the number of table index bits 36 0001eeee - length or distance, eeee is the number of extra bits 37 01100000 - end of block 38 01000000 - invalid code 39 */ 40 41 /* Maximum size of the dynamic table. The maximum number of code structures is 42 1444, which is the sum of 852 for literal/length codes and 592 for distance 43 codes. These values were found by exhaustive searches using the program 44 examples/enough.c found in the zlib distribution. The arguments to that 45 program are the number of symbols, the initial root table size, and the 46 maximum bit length of a code. "enough 286 9 15" for literal/length codes 47 returns 852, and "enough 30 6 15" for distance codes returns 592. The 48 initial root table size (9 or 6) is found in the fifth argument of the 49 inflate_table() calls in inflate.c and infback.c. If the root table size is 50 changed, then these maximum sizes would be need to be recalculated and 51 updated. */ 52 #define ENOUGH_LENS 852 53 #define ENOUGH_DISTS 592 54 #define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS) 55 56 /* Type of code to build for inflate_table() */ 57 typedef enum { 58 CODES, 59 LENS, 60 DISTS 61 } codetype; 62 63 static int ZLIB_INTERNAL inflate_table(codetype type, unsigned short FAR *lens, 64 unsigned codes, code FAR * FAR *table, 65 unsigned FAR *bits, unsigned short FAR *work); 66 67 #endif /* !INFTREES_H */