Re: [HACKERS] More Hashing questions
"Jim C. Nasby" <[EMAIL PROTECTED]> writes: > If you do this I suggest supporting bigint as well. Well I'm not about to actually do the inter-data-type hash joins. I was just asking if the hash functions for floats should be adjusted to guarantee this property. bigints already guarantee it, though I think the hash function can be improved without breaking it. > On Tue, May 04, 2004 at 06:45:37PM -0400, Greg Stark wrote: > > > > Regarding inter-data-type hash joins, would it make sense to make float > > datatypes to hash to the same value as integral data types for integral > > values? I have a little patch but I have to test it, at least try to compile it, before I send it anywhere :) -- greg ---(end of broadcast)--- TIP 7: don't forget to increase your free space map settings
Re: [HACKERS] More Hashing questions
If you do this I suggest supporting bigint as well.
On Tue, May 04, 2004 at 06:45:37PM -0400, Greg Stark wrote:
>
> Regarding inter-data-type hash joins, would it make sense to make float
> datatypes to hash to the same value as integral data types for integral
> values?
>
> Conveniently this would cover the existing special case of -0 and +0 hashing
> to the same value. Something like this?
>
> Datum
> hashfloat4(PG_FUNCTION_ARGS)
> {
> float4 key = PG_GETARG_FLOAT4(0);
>
> if (key == (int32)key)
> PG_RETURN_UINT32(~(int32)key);
>
> return hash_any((unsigned char *) &key, sizeof(key));
> }
>
>
> Incidentally, why do all the floatfoo functions invert the value? It doesn't
> seem like that affects the quality of the hash at all.
>
>
> --
> greg
>
>
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>
--
Jim C. Nasby, Database Consultant [EMAIL PROTECTED]
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[HACKERS] More Hashing questions
Regarding inter-data-type hash joins, would it make sense to make float
datatypes to hash to the same value as integral data types for integral
values?
Conveniently this would cover the existing special case of -0 and +0 hashing
to the same value. Something like this?
Datum
hashfloat4(PG_FUNCTION_ARGS)
{
float4 key = PG_GETARG_FLOAT4(0);
if (key == (int32)key)
PG_RETURN_UINT32(~(int32)key);
return hash_any((unsigned char *) &key, sizeof(key));
}
Incidentally, why do all the floatfoo functions invert the value? It doesn't
seem like that affects the quality of the hash at all.
--
greg
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