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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/87744] Some valid instantiations of
 linear_congruential_engine produce compiler errors when __int128 isn't
 available
Date: Tue, 06 Feb 2024 21:32:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D87744

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> Created attachment 57345 [details]
> Use 64-bit integers to do 128-bit arithmetic
>=20
> This patch defines a custom type that implements the necessary 128-bit
> arithmetic for linear_congruential_engine<uint64_t, ...> without __int128.
>=20
> It's an order of magnitude slower than using __int128 natively on x86_64,
> but it gives the right results.

            if (__builtin_uaddll_overflow(__l._M_lo, __c, &__l._M_lo))
              __l._M_hi++;

Why not just
            __l._M_hi +=3D __builtin_uaddll_overflow(__l._M_lo, __c, &__l._=
M_lo);
and similarly for subtraction?
Is the reason for using the clang compat builtins instead of
__builtin_{add,sub,mul}_overflow the compatibility with clang versions which
don't
support these?=