Date: Fri, 28 Dec 2007 07:42:15 -0500 From: "Aryeh M. Friedman" <aryeh.friedman@gmail.com> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: BSD license compatible hash algorithm? Message-ID: <4774EF27.90307@gmail.com> In-Reply-To: <fl2qiv$qoh$1@ger.gmane.org> References: <5950EE0C-383D-4D6B-9991-A0DEABD2ADE4@u.washington.edu> <20071228003716.GB48997@lor.one-eyed-alien.net> <B8D4C3C6-B867-4550-9F17-4DC6930D10E2@u.washington.edu> <fl2qiv$qoh$1@ger.gmane.org>
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Ivan Voras wrote:
> Garrett Cooper wrote:
>
>> Looks promising, but how difficult would it be to port the code
>> to other platforms (Win32 for instance?).
>
> The hash algorithm itself as implemented in hash.h is pretty much a
> text-book hash algorithm (D.J.Bernstein's):
>
> #ifndef HASHINIT
> #define HASHINIT 5381
> #define HASHSTEP(x,c) (((x << 5) + x) + (c))
> #endif
>
> /*
> * Return a 32-bit hash of the given buffer. The init
> * value should be 0, or the previous hash value to extend
> * the previous hash.
> */
> static __inline uint32_t
> hash32_buf(const void *buf, size_t len, uint32_t hash)
> {
> const unsigned char *p = buf;
>
> while (len--)
> hash = HASHSTEP(hash, *p++);
>
> return hash;
> }
>
> It apparently has some weaknesses if used on binary (non-text) data
> but I don't see why it wouldn't work on Windows.
All hashs have issues with pooling.... see
http://www.burtleburtle.net/bob/hash/index.html... btw it is a old
wives tale that the number of buckets should be prime (mostly based on
the very weak implementation Knuth offered)
- --
Aryeh M. Friedman
FloSoft Systems
http://www.flosoft-systems.com
Developer, not business, friendly
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