1 /* SPDX-License-Identifier: Zlib */ 2 /* inftrees.h -- header to use inftrees.c 3 * Copyright (C) 1995-2005, 2010 Mark Adler 4 * For conditions of distribution and use, see copyright notice in zlib.h 5 */ 6 7 /* WARNING: this file should *not* be used by applications. It is 8 part of the implementation of the compression library and is 9 subject to change. Applications should only use zlib.h. 10 */ 11 12 /* Structure for decoding tables. Each entry provides either the 13 information needed to do the operation requested by the code that 14 indexed that table entry, or it provides a pointer to another 15 table that indexes more bits of the code. op indicates whether 16 the entry is a pointer to another table, a literal, a length or 17 distance, an end-of-block, or an invalid code. For a table 18 pointer, the low four bits of op is the number of index bits of 19 that table. For a length or distance, the low four bits of op 20 is the number of extra bits to get after the code. bits is 21 the number of bits in this code or part of the code to drop off 22 of the bit buffer. val is the actual byte to output in the case 23 of a literal, the base length or distance, or the offset from 24 the current table to the next table. Each entry is four bytes. */ 25 typedef struct { 26 unsigned char op; /* operation, extra bits, table bits */ 27 unsigned char bits; /* bits in this part of the code */ 28 unsigned short val; /* offset in table or code value */ 29 } code; 30 31 /* op values as set by inflate_table(): 32 00000000 - literal 33 0000tttt - table link, tttt != 0 is the number of table index bits 34 0001eeee - length or distance, eeee is the number of extra bits 35 01100000 - end of block 36 01000000 - invalid code 37 */ 38 39 /* Maximum size of the dynamic table. The maximum number of code structures is 40 1444, which is the sum of 852 for literal/length codes and 592 for distance 41 codes. These values were found by exhaustive searches using the program 42 examples/enough.c found in the zlib distribtution. The arguments to that 43 program are the number of symbols, the initial root table size, and the 44 maximum bit length of a code. "enough 286 9 15" for literal/length codes 45 returns returns 852, and "enough 30 6 15" for distance codes returns 592. 46 The initial root table size (9 or 6) is found in the fifth argument of the 47 inflate_table() calls in inflate.c and infback.c. If the root table size is 48 changed, then these maximum sizes would be need to be recalculated and 49 updated. */ 50 #define ENOUGH_LENS 852 51 #define ENOUGH_DISTS 592 52 #define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS) 53 54 /* Type of code to build for inflate_table() */ 55 typedef enum { 56 CODES, 57 LENS, 58 DISTS 59 } codetype; 60 61 int ZLIB_INTERNAL inflate_table OF((codetype type, unsigned short FAR *lens, 62 unsigned codes, code FAR * FAR *table, 63 unsigned FAR *bits, unsigned short FAR *work)); 64