On Sun, Aug 04, 2013 at 05:38:55PM +0800, lx wrote:
> hi all:
> In the function of link_path_walk() , it counts the hash value of the
> compoent of the pathname.
> Why "(prevhash + (c <<4) + (c >> 4))*11;"?
In the code you quoted it says:
/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
A bit of googling led me to this[1] page, where it says:
r5 - This hash is a modified version of rupasov hash. It is used by
default and it is better to stick here until you have to support
huge directories and unusual file-name patterns.
and:
rupasov - This hash is invented by Yury Yu. Rupasov. It is fast and
preserves locality, mapping lexicographically close file names to
the close hash values. Never use it, as it has a high probability
of hash collisions.
[1] https://reiser4.wiki.kernel.org/index.php/Mount
Reading the ReiserFS code and/or mailing lists might give you a clue
about how the R5 hash was designed.
HTH,
Jonathan Neuschäfer
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