> std::numeric_limits<fas::Float<std::int16_t, std::int8_t>>::MAX()
Surely you mean ::max()?
> is_fundamental<int16_t, int16_t>::value et al.
Besides the undefined behavior issue mentioned by others, none of these are syntactially correct.
> #include "fas/stream.hpp>
Ok then...
> The Stl's std::numeric_limits is required the limits of the specified types for mantissa and exponent.
Missing a word? Also, the STL [0] does not have std::numeric_limits, perhaps you mean the C++ standard library (or stdlib for short).