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<  Erlang questions mailing list  ~  Strange behaviour of =:= applied to int and int64
Guest
Posted: Wed Sep 07, 2011 1:42 pm Reply with quote
Guest
I'm using R14B03 and writing a little NIF library. Today I've
encountered a strange behaviour of =:= when it is used against number
that is set in sources and term that was constructed as
enif_make_unit64. Here is an example:

(circa_dev@localhost)1> {ok, T} = ecirca:new(5, last, small).
{ok,{ecirca,#Ref<0.0.0.57>,<<>>,<0.48.0>,small}}
(circa_dev@localhost)2> {ok, A} = ecirca:size(T).
{ok,5}
(circa_dev@localhost)3> B = 5.
5
(circa_dev@localhost)4> A == B.
true
(circa_dev@localhost)5> A =:= B.
false
(circa_dev@localhost)6> A.
5
(circa_dev@localhost)7> B.
5

This behaviour looks quite weird to me. Is it expected?
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Guest
Posted: Wed Sep 07, 2011 5:49 pm Reply with quote
Guest
There was a recent thread related to the halfword emulator that would
cause this behavior. Not sure if its the same bug or not, but the
thread has a patch that fixed it for me.

Thread starts at [1] and the patch is at [2].


[1] http://erlang.org/pipermail/erlang-questions/2011-June/059650.html
[2] http://erlang.org/pipermail/erlang-questions/2011-June/059728.html

On Wed, Sep 7, 2011 at 9:49 AM, Dmitry Groshev <lambdadmitry@gmail.com> wrote:
>>Is it possible that you've made a "big" integer with a value of 5 in
> your NIF
> I'm not sure how BEAM handle enif_make_uint64, but I think that it would be
> strange if BEAM represent such numbers as "big integers".
> Anyway, it's a clear abstraction leak.
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@erlang.org
> http://erlang.org/mailman/listinfo/erlang-questions
>
>
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Guest
Posted: Thu Sep 08, 2011 1:58 pm Reply with quote
Guest
I'm more interested in fixing this behaviour in future releases than patching BEAM myself, because I can easily avoid this error. Is there any hope for this?
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Guest
Posted: Thu Sep 08, 2011 2:18 pm Reply with quote
Guest
> I'm more interested in fixing this behaviour in future releases than
> patching BEAM myself, because I can easily avoid this error. Is
> there any hope for this?

Yes, the patch in question has been applied to the dev branch:

https://github.com/erlang/otp/blob/dev/erts/emulator/beam/erl_nif.c

and will thus appear in R14B04, due to be released on 5th October IIRC.

Regards,
--
Magnus Henoch
Erlang Solutions Ltd
http://www.erlang-solutions.com/
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Guest
Posted: Fri Sep 09, 2011 4:43 pm Reply with quote
Guest
Magnus Henoch wrote:
>> I'm more interested in fixing this behaviour in future releases than
>> patching BEAM myself, because I can easily avoid this error. Is
>> there any hope for this?
>>
>
> Yes, the patch in question has been applied to the dev branch:
>
> https://github.com/erlang/otp/blob/dev/erts/emulator/beam/erl_nif.c
>
> and will thus appear in R14B04, due to be released on 5th October IIRC.
>
> Regards,
>
The mentioned patch in dev for R14B04 does only apply for halfword emulator:

https://github.com/erlang/otp/commit/1c0966044b66d20f3f6607e91076e0a61918f1a4

So... are you running halfword emulator, Dmitry.

/Sverker, Erlang/OTP

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Guest
Posted: Fri Sep 09, 2011 4:48 pm Reply with quote
Guest
yes.
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