inftrees.h

00001 /* inftrees.h -- header to use inftrees.c
00002  * Copyright (C) 1995-2005, 2010 Mark Adler
00003  * For conditions of distribution and use, see copyright notice in zlib.h
00004  */
00005 
00006 /* WARNING: this file should *not* be used by applications. It is
00007    part of the implementation of the compression library and is
00008    subject to change. Applications should only use zlib.h.
00009  */
00010 
00011 /* Structure for decoding tables.  Each entry provides either the
00012    information needed to do the operation requested by the code that
00013    indexed that table entry, or it provides a pointer to another
00014    table that indexes more bits of the code.  op indicates whether
00015    the entry is a pointer to another table, a literal, a length or
00016    distance, an end-of-block, or an invalid code.  For a table
00017    pointer, the low four bits of op is the number of index bits of
00018    that table.  For a length or distance, the low four bits of op
00019    is the number of extra bits to get after the code.  bits is
00020    the number of bits in this code or part of the code to drop off
00021    of the bit buffer.  val is the actual byte to output in the case
00022    of a literal, the base length or distance, or the offset from
00023    the current table to the next table.  Each entry is four bytes. */
00024 typedef struct {
00025     unsigned char op;           /* operation, extra bits, table bits */
00026     unsigned char bits;         /* bits in this part of the code */
00027     unsigned short val;         /* offset in table or code value */
00028 } code;
00029 
00030 /* op values as set by inflate_table():
00031     00000000 - literal
00032     0000tttt - table link, tttt != 0 is the number of table index bits
00033     0001eeee - length or distance, eeee is the number of extra bits
00034     01100000 - end of block
00035     01000000 - invalid code
00036  */
00037 
00038 /* Maximum size of the dynamic table.  The maximum number of code structures is
00039    1444, which is the sum of 852 for literal/length codes and 592 for distance
00040    codes.  These values were found by exhaustive searches using the program
00041    examples/enough.c found in the zlib distribtution.  The arguments to that
00042    program are the number of symbols, the initial root table size, and the
00043    maximum bit length of a code.  "enough 286 9 15" for literal/length codes
00044    returns returns 852, and "enough 30 6 15" for distance codes returns 592.
00045    The initial root table size (9 or 6) is found in the fifth argument of the
00046    inflate_table() calls in inflate.c and infback.c.  If the root table size is
00047    changed, then these maximum sizes would be need to be recalculated and
00048    updated. */
00049 #define ENOUGH_LENS 852
00050 #define ENOUGH_DISTS 592
00051 #define ENOUGH (ENOUGH_LENS+ENOUGH_DISTS)
00052 
00053 /* Type of code to build for inflate_table() */
00054 typedef enum {
00055     CODES,
00056     LENS,
00057     DISTS
00058 } codetype;
00059 
00060 int ZLIB_INTERNAL inflate_table OF((codetype type, unsigned short FAR *lens,
00061                              unsigned codes, code FAR * FAR *table,
00062                              unsigned FAR *bits, unsigned short FAR *work));