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From: "post+gcc at ralfj dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/112449] Arithmetic operations can produce signaling NaNs
Date: Thu, 09 Nov 2023 06:46:56 +0000	[thread overview]
Message-ID: <bug-112449-4-mynw4j31ak@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-112449-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112449

--- Comment #6 from post+gcc at ralfj dot de ---
Hm, OTOH the C standard says

> The expressions 1×x, x/1, and x are equivalent (on IEC 60559 machines, among
others).

So, it seems like when they say "The + ,- , * , and / operators provide the IEC
60559 add, subtract, multiply, and divide operations.", they don't quite mean
that.

This seems internally inconsistent in the C standard, since C also permits
`pow(1, sNaN)` to behave different from `pow(1, qNaN)` -- and in fact they do
behave different in GNU's libm. So on the one hand `pow(1, x * y)` must always
be `1` but on the other hand it can return a NaN when `x` is an sNaN and `y` is
`1`?

  parent reply	other threads:[~2023-11-09  6:46 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-08 21:03 [Bug c/112449] New: " post+gcc at ralfj dot de
2023-11-08 21:11 ` [Bug c/112449] " pinskia at gcc dot gnu.org
2023-11-08 21:18 ` pinskia at gcc dot gnu.org
2023-11-08 21:40 ` pinskia at gcc dot gnu.org
2023-11-08 21:43 ` pinskia at gcc dot gnu.org
2023-11-09  6:40 ` post+gcc at ralfj dot de
2023-11-09  6:46 ` post+gcc at ralfj dot de [this message]
2023-11-09  6:56 ` post+gcc at ralfj dot de
2023-11-09  7:57 ` rguenth at gcc dot gnu.org
2023-11-09 17:53 ` joseph at codesourcery dot com
2023-11-09 20:33 ` post+gcc at ralfj dot de
2023-11-10  8:15 ` rguenth at gcc dot gnu.org
2023-11-10 10:27 ` post+gcc at ralfj dot de
2023-11-13 22:46 ` joseph at codesourcery dot com

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