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Subject[QUESTION] omit adler32 in zlib
Hello,

zlib deflate generates an adler32 checksum for the input uncompressed
data. In order to gain some drop of performance we would like not to
generate/check adler32 because we anyway protect our data by much stronger
CRC32.

How to correctly do that?

My quick investigation has shown that it is possible if I pass the a
negative windowBits parameter to the deflateInit2() function to achieve
the goal. But this feature isn't noted in the deflate API description
(include/linux/zlib.h) and is called "undocumented feature" in
lib/zlib_deflate/deflate.c.

So the question is: is it OK to use this undocumented feature? What are
alternatives?

I also noted that if I use deflate via crypto API, I'll get what I want
since it does:

#define DEFLATE_DEF_WINBITS 11
ret = zlib_deflateInit2(stream,
DEFLATE_DEF_LEVEL,
Z_DEFLATED,
-DEFLATE_DEF_WINBITS,
DEFLATE_DEF_MEMLEVEL,
Z_DEFAULT_STRATEGY);

(note the "minus" character before DEFLATE_DEF_WINBITS)

I'm curious why crypto API omits adler32 by default?

Thanks.

--
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.
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