typedef float_fast#_t, with
# replaced by the width, designates the fastest
floating-point type with a width of at least # bits.
There is no absolute guarantee that these types are the fastest for all purposes. In any case, however, they satisfy the precision and width requirements.
Fastest minimum-width floating-point types are provided for all existing exact-width floating-point types on a given platform.
For example, if a platform supports
will also be supported, etc.