From owner-freebsd-hackers  Fri Apr 25 22:49:28 1997
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To: "Daniel C. Sobral" <dcs@gns.com.br>
cc: hackers@hub.freebsd.org
Subject: Re: namei & hash functions 
In-reply-to: Your message of "Fri, 25 Apr 1997 18:41:04 -0300."
             <199704252142.SAA04687@gns.com.br> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Fri, 25 Apr 1997 22:50:44 -0700
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>> Index: vfs_lookup.c
>> ===================================================================
>> RCS file: /jaz/cvs/src/sys/kern/vfs_lookup.c,v
>> retrieving revision 1.11.4.1
>> diff -r1.11.4.1 vfs_lookup.c
>> 271a272
>> > 	u_long hash;
>> 299c300
>> < 	cnp->cn_hash = 0;
>> - ---
>> > 	hash = 0;
>> 301c302,303
>> < 		cnp->cn_hash += (unsigned char)*cp;
>> - ---
>> > 		hash = hash * 33 + (unsigned char)*cp;
>
>I think		hash += hash << 5 + (unsigned char)*cp;
>would be better...
>
>> > 	cnp->cn_hash = hash;

   Only the bottom so-many bits are going to be involved in the hash index. I
think you lose too much by shifting useful bits off the end.

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project