From: Proton (matt_at_[hidden])
Date: 2022-08-21 21:25:20
> On Aug 21, 2022, at 1:26 PM, Gero Peterhoff via Boost <boost_at_[hidden]> wrote:
> Am 19.08.22 um 03:53 schrieb Proton via Boost:
>> Using __builtin_bit_cast should be fine for conditional C++17 support since we already rely on __builtin_is_constant_evaluated. Iâll play with it this weekend and see where it get us. Worst case is we static_assert unsupported cases like John suggested.
> Hi Matt,
> I see that you have started work on ccmath::signbit/copysign/etc. I also. Our basic problem is that std::bit_cast is only available with C++20. You are already trying to provide this for C++17 (BOOST_MATH_BIT_CAST). My questions:
> - can you *guarantee* that BOOST_MATH_BIT_CAST works on/with all platforms/compilers ?
> - if not: does it make sense to upgrade ccmath to C++20 so that std::bit_cast is available ?
> Otherwise I can only oracle and provide code to the best of my knowledge - without guarantee that it works on/with all platforms/compilers :-(
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
I can make no such guarantees. I do not think it makes sense to upgrade to C++20 because BOOST_MATH_BIT_CAST macro enables C++17 support. If you look at the comments even with a move to C++20 Clang does not yet support constexpr std::bit_cast/__builtin_bit_cast with bit-fields. I have provided layouts for 64, 80, and 128 bit long doubles so most platforms should be covered if the toolchain supports it.
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk