An Rc=1 variant tests not against RT but RA, which allows detection
of a fixup in Knuth Algorithm D: the condition where RA is not zero.
-# EXT004 Opcode map
-
-See Power ISA v3.1, Book III, Appendix D, Table 13 (sheet 7 of 8), p1357.
-Proposed is the addition of `msubxd` (**DRAFT, NOT APPROVED**) which is
-in `110110`. A corresponding `maddxd` is proposed for `110010`
-
-| 110000 | 110001 | 110010 | 110011 | 110100 | 110101 | 110110 | 110111 |
-| ------ | ------- | ------ | ------ | ------ | ------ | ------ | ------ |
-| maddhd | maddhdu | maddxd | maddld | rsvd | rsvd | msubxd | rsvd |