[geos-devel] Ticket #202 (double hash)

[Mateusz Loskot]

Ben Harper wrote:
> Apologies for sending this to the entire list, but I couldn't figure
> out how to comment on the ticket alone. I created an OSGeo user
> account, and logged in to trac, but still no GUI available.

Ben,

This is strange. Perhaps you could report this problem to SAC
mailing list: http://lists.osgeo.org/mailman/listinfo/sac

> Anyway, concerning an I32 hash on a double, I think the easiest naive
> solution that does not have terrible performance concerns is:
> 
> unsigned int HashDouble( double d )
 > {
 >   unsigned int* i = (unsigned int*) &d;

This construction breaks strict aliasing rules,
so it's undefined behavior.

 >   return i[0] ^ i[1];
 > }

Yes, this is popular hack, however AFAIK it doesn't promise no 
duplication will occur.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org