1  /* inftrees.h  header to use inftrees.c


2  * Copyright (C) 19952005, 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 endofblock, 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));

