[Zlib-devel] Deflate 64 and zLib

[Gilles Vollant]

unzip 5.5 introduced support of Deflate64 compression format
 
Just for info, inflate.c of unzip 5.5 say
The Deflate64 (PKZIP method 9) variant of the compression algorithm
differs from "classic" deflate in the following 3 aspect:
a) The size of the sliding history window is expanded to 64 kByte.
b) The previously unused distance codes #30 and #31 code distances
   from 32769 to 49152 and 49153 to 65536.  Both codes take 14 bits
   of extra data to determine the exact position in their 16 kByte
   range.
c) The last lit/length code #285 gets a different meaning. Instead
   of coding a fixed maximum match length of 258, it is used as a
   "generic" match length code, capable of coding any length from
   3 (min match length + 0) to 65538 (min match length + 65535).
   This means that the length code #285 takes 16 bits (!) of uncoded
   extra data, added to a fixed min length of 3.
Changes a) and b) would have been transparent for valid deflated
data, but change c) requires to switch decoder configurations between
Deflate and Deflate64 modes.
 
 
 
Do you known if we can imagine a zLib that support Deflate64 stream ?
 
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