llvm dev - Jun 2017 - Semantics of fdiv division by zero

Hey guys,

I am wondering what the semantics for fdiv is, if the denominator is
zero. For sdiv, the language reference specifies that this is undefined
behavior. For fdiv, the language reference says nothing (hence, I assume
that it is defined somehow).

So how is it defined? Does it follow IEEE-754 definition, i.e., +Inf if
nominator is > 0, -Inf if nominator is < 0, otherwise NaN?

Regards,

Jan Finis

Maybe the semantic somehow implied by [1], but I think it's desired a
better definition.

[1] http://llvm.org/docs/LangRef.html#fast-math-flags

2017-06-22 23:04 GMT+08:00 Jan Finis via llvm-dev <llvm-dev at
lists.llvm.org>:
> Hey guys,
>
> I am wondering what the semantics for fdiv is, if the denominator is
> zero. For sdiv, the language reference specifies that this is undefined
> behavior. For fdiv, the language reference says nothing (hence, I assume
> that it is defined somehow).
>
> So how is it defined? Does it follow IEEE-754 definition, i.e., +Inf if
> nominator is > 0, -Inf if nominator is < 0, otherwise NaN?
>
> Regards,
>
> Jan Finis
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>


-- 
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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Unfortunately, no flag in [1] mentions anything about devision by zero. So it
still seems
that there is no place in the reference where anything is stated about the
semantics of it.

On 22/06/17 17:27, 陳韋任 wrote:
Maybe the semantic somehow implied by [1], but I think it's desired a better
definition.

[1] http://llvm.org/docs/LangRef.html#fast-math-flags

2017-06-22 23:04 GMT+08:00 Jan Finis via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>:
Hey guys,

I am wondering what the semantics for fdiv is, if the denominator is
zero. For sdiv, the language reference specifies that this is undefined
behavior. For fdiv, the language reference says nothing (hence, I assume
that it is defined somehow).

So how is it defined? Does it follow IEEE-754 definition, i.e., +Inf if
nominator is > 0, -Inf if nominator is < 0, otherwise NaN?

Regards,

Jan Finis




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llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
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--
Wei-Ren Chen (陳韋任)
Homepage:
https://people.cs.nctu.edu.tw/~chenwj<https://people.cs.nctu.edu.tw/%7Echenwj>

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On 06/22/2017 10:04 AM, Jan Finis via llvm-dev wrote:
> Hey guys,
>
> I am wondering what the semantics for fdiv is, if the denominator is
> zero. For sdiv, the language reference specifies that this is undefined
> behavior. For fdiv, the language reference says nothing (hence, I assume
> that it is defined somehow).
>
> So how is it defined? Does it follow IEEE-754 definition, i.e., +Inf if
> nominator is > 0, -Inf if nominator is < 0, otherwise NaN?
That's correct (it follows the semantics for the underlying type, which 
is generally IEEE with default rounding).

  -Hal
>
> Regards,
>
> Jan Finis
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory