For every fixed-point type S, S'Fixed_Value denotes a
function with the following specification:
function S'Fixed_Value (Arg : <Universal_Integer>) return S;
The value returned is the fixed-point value V such that:
V = Arg * S'Small
The effect is thus similar to first converting the argument to the
integer type used to represent S, and then doing an unchecked
conversion to the fixed-point type. The difference is
that there are full range checks, to ensure that the result is in range.
This attribute is primarily intended for use in implementation of the
input-output functions for fixed-point values.