# ../extmod/modtrezorutils/modtrezorutils.c
def memcpy(dst: bytearray, dst_ofs: int,
                        src: bytearray, src_ofs: int,
    '''
    Copies at most `n` bytes from `src` at offset `src_ofs` to
    `dst` at offset `dst_ofs`.  Returns the number of actually
    copied bytes.
    '''