zlib/inftrees.h

   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));