This is only available from C++23, but the implementation is fairly trivial
and the old variants of BSWAP32/BSWAP16 were not constexpr on MSVC. This was
due to all kinds of intrinsics that were added to get better code. However,
recent compilers with reasonable optimisation settings see the naive code and
will inject the appropriate optimised code (bswap op on x86-64).
For x86-64 recent is: Clang 6+ -O1, GCC 6+ -O2, MSVC 19.34+ /O1.
Rubidium
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