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List:       rsync
Subject:    Re: default value for --compress-level
From:       "Benjamin R. Haskell" <rsync () benizi ! com>
Date:       2010-09-15 13:16:40
Message-ID: alpine.LNX.2.01.1009150910490.4535 () hp
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On Tue, 14 Sep 2010, Tomasz Chmielewski wrote:

> What is the default value for --compress-level=? 6? 9?
>
> The fine manual only mentions:
>
>       --compress-level=NUM
>              Explicitly set the compression level to use (see
>              --compress) instead of letting it default.  If NUM is
>              non-zero, the --compress option is implied.
>
>
> Also, what are allowed values? 1-9? 0-9? Something else?

From a comment in zlib/zlib.h in the source:

"""
The compression level must be Z_DEFAULT_COMPRESSION, or between 0 and 9: 
1 gives best speed, 9 gives best compression, 0 gives no compression at 
all (the input data is simply copied a block at a time). 
Z_DEFAULT_COMPRESSION requests a default compromise between speed and 
compression (currently equivalent to level 6).
"""

Z_DEFAULT_COMPRESSION is defined as (-1), and appears to be the value 
used if --compress is specified without --compress-level, making the 
default functionally equivalent to 6.

-- 
Best,
Ben
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