BSD license compatible hash algorithm?

Aryeh M. Friedman aryeh.friedman at gmail.com
Fri Dec 28 05:12:28 PST 2007


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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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