move_subword
#define move_lower_bits(target, target_bit, src, src_bit) move_subword(target, target_bit, src, 0, src_bit)
#define move_upper_bits(target, target_bit, src, src_bit) move_subword(target, target_bit, src, src_bit, uedge_bits)
#define move_word(target, target_bit, src) move_subword(target, target_bit, src, 0, uedge_bits)
move_subword(elem, 0, vector[start_elem], start_bit, end_bit);