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From: "harald at gigawatt dot nl" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/100805] __int128 should be disabled for non-extended -std=
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Date: Thu, 27 May 2021 22:32:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100805

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at gigawatt dot nl

--- Comment #2 from Harald van Dijk <harald at gigawatt dot nl> ---
(In reply to Andreas Schwab from comment #1)
> The C++ standard says: [lex.icon] "If an integer literal cannot be
> represented by any type in its list and an extended integer type (6.8.1) =
can
> represent its value, it may have that extended integer type."

__int128 behaves mostly like an integer type but is not an "extended integer
type" as defined in the standard. Quoting from
https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html: "GCC does =
not
support any extended integer types." Extended integer types must meet speci=
fic
requirements that __int128 does not meet: extended integer types cannot be
larger than intmax_t, and __int128 is.

Despite __int128 not being an extended integer type, there is nothing wrong
with having __int128 enabled in standards-conforming mode. Out-of-range
constants must be diagnosed, but they already are, and continuing to accept=
 the
program after that is valid.

The warning that is generated for the out-of-range constant is highly
misleading though: the warning says "integer constant is so large that it is
unsigned". Either the constant should be given an unsigned type, or the war=
ning
should be updated to reflect the type the constant actually gets.=