[erlang-patches] [PATCH] - Add NIF function enif_phash2

Paul Davis <>
Fri Feb 8 21:19:38 CET 2013


Fredrik,

Rebased against master:

git fetch git://github.com/davisp/otp.git enif_phash2

https://github.com/davisp/otp/compare/master...enif_phash2
https://github.com/davisp/otp/compare/master...enif_phash2.patch

Sverker,

I've updated the function ordering as per the comment in
erl_nif_api_funcs.h. For use case, I'm implementing a couple data
structures that use hash tables to speed up some hot loops. I can get
away for awhile using erlang:phash2/2 in Erlang and passing that value
into the NIF but this breaks down when I don't know a priori which
terms (or subterms) I may need to hash in the NIF.

A similar example would be trying to reimplement ets without this.
Either I'd have to store enough information in the Erlang term
representing the table to be able to know which elements of the tuple
to hash or I'd have to ask the table what to hash before passing the
term off to the NIF. There are definitely work arounds to not having
access to phash2 but they aren't pretty.

Thanks,
Paul Davis

On Fri, Feb 8, 2013 at 7:39 AM, Sverker Eriksson
<> wrote:
> Fredrik wrote:
>>
>> On 02/08/2013 12:58 AM, Paul Davis wrote:
>>>
>>> git fetch git://github.com/davisp/otp.git enif_phash2
>>>
>>> https://github.com/davisp/otp/compare/maint...enif_phash2
>>> https://github.com/davisp/otp/compare/maint...enif_phash2.patch
>>>
>>> This patch exposes the phash2 function to NIFs. It is exactly equivalent
>>> to:
>>>
>>> erlang:phash2(Term, 16#100000000)
>>>
>>> Thanks,
>>> Paul Davis
>>> _______________________________________________
>>> erlang-patches mailing list
>>> 
>>> http://erlang.org/mailman/listinfo/erlang-patches
>>
>> Please rebase this patch upon the current 'master' branch.
>> Thanks,
>>
> Also read the comments in erl_nif_api_funcs.h of how to add new functions.
> You do not have to increase ERL_NIF_MINOR_VERSION as I've already done that
> for R16B.
>
> I guess you have a real use case for enif_phash2 and why erlang:phash2 is
> not enough.
>
> /Sverker


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