completely different from normal SVP64 `sz=0` behaviour)
* **CTR-test=1, CTi=0**: CTR decrements on a per-element basis
if `BO[2]` is zero and the Condition Test succeeds.
- Masked-out elements when `sz=0` are skipped.
+ Masked-out elements when `sz=0` are skipped (including
+ not decrementing CTR)
* **CTR-test=1, CTi=1**: CTR decrements on a per-element basis
if `BO[2]` is zero and the Condition Test *fails*.
- Masked-out elements when `sz=0` are skipped.
+ Masked-out elements when `sz=0` are skipped (including
+ not decrementing CTR)
`CTR-test=0, CTi=1, sz=0` requires special emphasis because it is the
only time in the entirety of SVP64 that has side-effects when