The support includes:
- The standard fetch_add/fetch_sub operations.
- Extra operations: (fetch_/opaque_)negate, (opaque_)add/sub.
- Extra capability macros: BOOST_ATOMIC_FLOAT/DOUBLE/LONG_DOUBLE_LOCK_FREE.
The atomic operations are currently implemented on top of the integer-based
backends and thus are mostly CAS-based. The CAS operations perform binary
comparisons, and as such have different behavior wrt. special FP values like
NaN and signed zero than normal C++.
The support for floating point types is optional and can be disabled by
defining BOOST_ATOMIC_NO_FLOATING_POINT. This can be useful if on a certain
platform parameters of the floating point types cannot be deduced from the
compiler-defined or system macros (in which case the compilation fails).
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0020r6.html
