(no commit message)

diff --git a/openpower/sv/svp64/appendix.mdwn b/openpower/sv/svp64/appendix.mdwn
index bfbae889afeda5af7303df75e02b4eb1f416a95c..59c430468a89cfb03ba864687bdfe67a3b5f3e29 100644 (file)
--- a/openpower/sv/svp64/appendix.mdwn
+++ b/openpower/sv/svp64/appendix.mdwn
@@ -142,17 +142,21 @@ and if less than or equal to three then that instruction could be given an
 EXTRA3 designation.  Four or more is given an EXTRA2 designation because
 there are only 9 bits available.
 
-Thirdly, a packing format was decided: for 2R-1W an EXTRA3 indexing
+Thirdly, the instruction was analysed to see if Twin or Single
+Predication was suitable.  As a general rule this was if there
+was only a single operand and a single result (`extw` and LD/ST)
+however it was found that some 2 or 3 operand instructions also
+qualify. Given that 3 of the 9 bits of EXTRA had to be sacrificed for use
+in Twin Predication, some compromises were made, here.
+
+Fourthly, a packing format was decided: for 2R-1W an EXTRA3 indexing
 could have been decided
 that RA would be indexed 0 (EXTRA bits 0-2), RB indexed 1 (EXTRA bits 3-5)
 and RT indexed 2 (EXTRA bits 6-8).  In some cases (LD/ST with update)
 RA-as-a-source is given a **different** EXTRA index from RA-as-a-result
-(because it is possible to do, and perceived to be useful).
-
-Fourthly, the instruction was analysed to see if Twin or Single
-Predication was suitable.  As a general rule this was if there
-was only a single operand and a single result (`extw` and LD/ST)
-however some 2 or 3 operand instructions also qualify.
+(because it is possible to do, and perceived to be useful). Rc=1
+co-results (CR0, CR1) are always given the same EXTRA index as their
+main result (RT, FRT).
 
 Fifthly, in an automated process the results of the analysis
 were outputted in CSV Format for use in machine-readable form