only available in 16-bit mode, only available when M=1 and N=1
and when Cmaj.min is not 0b001.1.
+instruction counts from objdump on /bin/bash
+ 466 extsw r1,r1
+ 649 stw r1,1(r1)
+ 691 lwz r1,1(r1)
+ 705 cmpdi r1,1
+ 791 cmpwi r1,1
+ 794 addis r1,r1,1
+ 1474 std r1,1(r1)
+ 1846 li r1,1
+ 2031 mr r1,r1
+ 2473 addi r1,r1,1
+ 3012 nop
+ 3028 ld r1,1(r1)
+
+
| 0 | 1 | 2 | 3 4 | | 567.8 | 9ab | cde | f |
| 1 | 0 | 0 0 0 | | 001.0 | | 000 | 1 | TBD
| 1 | 0 | sh2 | | 001.0 | RA | sh | 1 | sradi.