From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2025-06-12 09:31:26
On 12 Jun 2025 11:24, Alexander Grund via Boost wrote:
>
> As for atomic enums: I wouldn't expect too much there as e.g. `config |=
> ConfigEnum::UseSimd` wouldn't be reliable for atomics without a
> compare&swap.
There are atomic instructions that implement bitwise operations
directly, without a CAS loop. Including on x86, although not in all cases.
> You noted that already for "user-defined bitwise operators defined for
> an enum,", so I guess you are aware of that already.
To be clear, I'm not suggesting that e.g. atomic<enum>::fetch_or()
should be calling the user-defined operator| for the enum. *That* would
require a CAS loop. No, I'm suggesting that atomic bitwise operations
should be defined in terms of value representations, pretty much how
compare_exchange_(weak|strong) is defined, which, as you know, compares
values "as if with memcmp" and does not invoke any user-defined
operator==().