Re: Ada.Containers Hash function for a set of small integers

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Fri, 23 Apr 2010 23:39:52 +0200, Simon Wright <simon@pushface.org> a  
écrit:
> I don't know about 'best', but in ColdFrame
> (http://coldframe.sourceforge.net/coldframe/) I would generate this hash
> for use with Booch Maps, where the key components of Instance are
> {A:Integer, B:Integer, C:Integer}:
>
>    function Instance_Hash (I : Instance) return Natural is
>       type M is mod 2**31;
>       Result : M := 0;
>    begin
>       Result := Result xor M (I.A mod 2**31);
>       Result := Result * 10019;
>       Result := Result xor M (I.B mod 2**31);
>       Result := Result * 10019;
>       Result := Result xor M (I.C mod 2**31);
>       Result := Result * 10019;
>       return Natural (Result);
>    end Instance_Hash;
>
> I believe the 10019 came from Knuth, but can't see a reference.
Unlucky, I was to ask you how this 10_019 was computed. At least, this  
magic number is not a prime number, the nearest is 1009.

If this can help, may be some goodies there :
http://www.isthe.com/chongo/tech/comp/fnv/
http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx

-- 
No-no, this isn't an oops ...or I hope (TM) - Don't blame me... I'm just  
not lucky