Software floating point operation library.
Many floating operations require a rounding mode and can set a few exception flags.
This library therefore expects two callbacks, softfp_get_rounding_mode and
softfp_set_exception_flags. You can define them with #[no_mangle]. The calling
convention is Rust, so there is no need for extern "C".
If you prefer not to define these callbacks with #[no_mangle], you can use the
enabled-by-default "register" feature which allow you to register the function
via register_get_rounding_mode and register_set_exception_flags instead.
You must register them before using the library for any floating point operations.
The simplest way would be track them using
thread_local!
variables.