FreeBSD/Linux Kernel Cross Reference
sys/contrib/zlib/inftrees.h

     /* 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.
      */
    
    /* 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 OF((codetype type, unsigned short FAR *lens,
                                 unsigned codes, code FAR * FAR *table,
                                 unsigned FAR *bits, unsigned short FAR *work));

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