From: Janne Blomqvist <blomqvist.janne@gmail.com>
To: Thomas Koenig <tkoenig@netcologne.de>
Cc: Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>,
Richard Biener <richard.guenther@gmail.com>,
"fortran@gcc.gnu.org" <fortran@gcc.gnu.org>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH][Fortran] Use MIN/MAX_EXPR for intrinsics or __builtin_fmin/max when appropriate
Date: Tue, 17 Jul 2018 20:35:00 -0000 [thread overview]
Message-ID: <CAO9iq9HGgS5rXuHOVqY6F_uBGE8uakiLd5SMQEK3eenCC=EaTA@mail.gmail.com> (raw)
In-Reply-To: <CAO9iq9GYUswbCaU0_WOZ5tppNY7RU7mF26gEqA19F8aWMJtqvw@mail.gmail.com>
On Tue, Jul 17, 2018 at 11:06 PM, Janne Blomqvist <blomqvist.janne@gmail.com
> wrote:
> On Tue, Jul 17, 2018 at 6:36 PM, Thomas Koenig <tkoenig@netcologne.de>
> wrote:
>
>> Hi Kyrill,
>>
>> The current implementation expands to:
>>> mvar = a1;
>>> if (a2 .op. mvar || isnan (mvar))
>>> mvar = a2;
>>> if (a3 .op. mvar || isnan (mvar))
>>> mvar = a3;
>>> ...
>>> return mvar;
>>>
>>> That is, if one of the operands is a NaN it will return the other
>>> argument.
>>> If both (all) are NaNs, it will return NaN. This is the same as the
>>> semantics of fmin/max
>>> as far as I can tell.
>>>
>>
>> I've looked at the F2008 standard, and, interestingly enough, the
>> requirement on MIN and MAX do not mention NaNs at all. 13.7.106
>> has, for MAX,
>>
>> Result Value. The value of the result is that of the largest argument.
>>
>> plus some stuff about character variables (not relevant here). Similar
>> for MIN.
>>
>
> FWIW, this has not changed in the latest(?) draft for F2018 (N2146), see
> 16.9.125.
>
> Also, the section on IEEE_ARITHMETIC (14.9) does not mention
>> comparisons; also, "Complete conformance with IEC 60559:1989 is not
>> required", what is required is the correct support for +,-, and *,
>> plus support for / if IEEE_SUPPORT_DIVIDE is covered.
>>
>
> Interestingly, here the F2018 draft has new intrinsics in the
> IEEE_ARITHMETIC module, IEEE_MAX_NUM, IEEE_MAX_NUM_MAG, IEEE_MIN_NUM,
> IEEE_MIN_NUM_MAG. These correspond to the {max,min}num{,_mag} operations in
> IEEE 754-2008, which AFAICT has the same NaN semantics as __builtin_fmax
> etc.
>
>
>> So, the Fortran standard does not impose many requirements.
>
>
> If so, why don't we just use {MAX,MIN}_EXPR unconditionally? Those who
> worry about the behavior wrt. NaNs, infinities etc. can use the intrinsics
> from IEEE_ARITHMETIC?
>
>
> This thread also has some interesting discussion on the topic:
> https://github.com/JuliaLang/julia/issues/7866
>
Oh, and on http://754r.ucbtest.org/ there is information about the next
update after IEEE 754-2008. In particular,
http://754r.ucbtest.org/changes.html notes that the above mentioned
{max,min}num{,_mag} have been deleted, and "new
{min,max}imum{,Number,Magnitude,MagnitudeNumber} operations are
recommended; NaN and signed zero handling are changed from 754-2008 5.3.1.
".
--
Janne Blomqvist
next prev parent reply other threads:[~2018-07-17 20:35 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-17 12:35 Kyrill Tkachov
2018-07-17 13:27 ` Richard Biener
2018-07-17 13:46 ` Kyrill Tkachov
2018-07-17 15:37 ` Thomas Koenig
2018-07-17 16:16 ` Kyrill Tkachov
2018-07-17 17:42 ` Thomas Koenig
2018-07-17 20:06 ` Janne Blomqvist
2018-07-17 20:35 ` Janne Blomqvist [this message]
2018-07-18 11:17 ` [PATCH][Fortran][v2] Use MIN/MAX_EXPR for min/max intrinsics Kyrill Tkachov
2018-07-18 13:26 ` Thomas König
2018-07-18 14:03 ` Kyrill Tkachov
2018-07-18 14:55 ` Janne Blomqvist
2018-07-18 15:28 ` Richard Sandiford
2018-07-18 16:04 ` Kyrill Tkachov
2018-07-18 15:10 ` Janne Blomqvist
2018-07-26 20:36 ` Joseph Myers
2018-08-06 12:05 ` Janne Blomqvist
2018-07-18 9:44 ` [PATCH][Fortran] Use MIN/MAX_EXPR for intrinsics or __builtin_fmin/max when appropriate Richard Biener
2018-07-18 9:50 ` Kyrill Tkachov
2018-07-18 10:06 ` Richard Biener
2018-07-18 11:45 ` [PATCH]Use " Richard Sandiford
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