There are some corner cases where the C++ number promotion rules can hurt us badly.
Devised a type selection logic to pick a suitable common numeric type explicitly,
using `std::common_type<T1,T2>` in most cases, yet handling explicitly the
case when the computation would wrap into unsigned; in such a mixed sign integral case,
we either use int64_t (when its precision suffices), or long double,
which can hold 64bit of mantissa without precision loss.
Ichthyostega
e3a8ce1b5e