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

[Warren <ve3wwg@gmail.com>]

Simon Wright expounded in news:m28w8dyhjr.fsf@pushface.org:
..
> 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.

I think this is just a selected prime number:

 http://www.mathematical.com/primes3000kto4000k.html

Probably a compromise between "wideness" and memory
used in the map itself (affects number of buckets perhaps).

Warren.