GCC provides many FR-V-specific built-in functions. In general,
these functions are intended to be compatible with those described
by FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu
Semiconductor. The two exceptions are __MDUNPACKH and
__MBTOHE, the GCC forms of which pass 128-bit values by
pointer rather than by value.
Most of the functions are named after specific FR-V instructions. Such functions are said to be “directly mapped” and are summarized here in tabular form.