inftrees.h

Go to the documentation of this file.

/* inftrees.h -- header to use inftrees.c
 * Copyright (C) 1995-2005, 2010 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/* WARNING: this file should *not* be used by applications. It is
 part of the implementation of the compression library and is
 subject to change. Applications should only use zlib.h.
 */

#ifndef _INFTREES_H
#define _INFTREES_H

/* Structure for decoding tables. Each entry provides either the
 information needed to do the operation requested by the code that
 indexed that table entry, or it provides a pointer to another
 table that indexes more bits of the code. op indicates whether
 the entry is a pointer to another table, a literal, a length or
 distance, an end-of-block, or an invalid code. For a table
 pointer, the low four bits of op is the number of index bits of
 that table. For a length or distance, the low four bits of op
 is the number of extra bits to get after the code. bits is
 the number of bits in this code or part of the code to drop off
 of the bit buffer. val is the actual byte to output in the case
 of a literal, the base length or distance, or the offset from
 the current table to the next table. Each entry is four bytes. */
typedef struct {
 unsigned char op; /* operation, extra bits, table bits */
 unsigned char bits; /* bits in this part of the code */
 unsigned short val; /* offset in table or code value */
} code;

/* op values as set by inflate_table():
 00000000 - literal
 0000tttt - table link, tttt != 0 is the number of table index bits
 0001eeee - length or distance, eeee is the number of extra bits
 01100000 - end of block
 01000000 - invalid code
 */

/* Maximum size of the dynamic table. The maximum number of code structures is
 1444, which is the sum of 852 for literal/length codes and 592 for distance
 codes. These values were found by exhaustive searches using the program
 examples/enough.c found in the zlib distribtution. The arguments to that
 program are the number of symbols, the initial root table size, and the
 maximum bit length of a code. "enough 286 9 15" for literal/length codes
 returns returns 852, and "enough 30 6 15" for distance codes returns 592.
 The initial root table size (9 or 6) is found in the fifth argument of the
 inflate_table() calls in inflate.c and infback.c. If the root table size is
 changed, then these maximum sizes would be need to be recalculated and
 updated. */
#define ENOUGH_LENS 852
#define ENOUGH_DISTS 592
#define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS)

/* Type of code to build for inflate_table() */
typedef enum {
 CODES,
 LENS,
 DISTS
} codetype;

int ZLIB_INTERNAL inflate_table (codetype type, unsigned short FAR *lens,
 unsigned codes, code FAR * FAR *table,
 unsigned FAR *bits, unsigned short FAR *work);

#endif