isa/bcd.mdwn: update addg6s pseudocode

Not only this pseudocode is wrong, since some actions are put inside
the loop, but also the algorithm as is cannot be translated due to
use of function call (carry_out). For more details, check these
discussions:

	https://libre-soc.org/irclog/%23libre-soc.2021-07-28.log.html
	https://bugs.libre-soc.org/show_bug.cgi?id=656

diff --git a/openpower/isa/bcd.mdwn b/openpower/isa/bcd.mdwn
index 30bb161905b9f422bf014807a2b91c7772e1a665..04753ed645431887d55368f6940adfca782e2b42 100644 (file)
--- a/openpower/isa/bcd.mdwn
+++ b/openpower/isa/bcd.mdwn
@@ -33,13 +33,15 @@ XO-Form
 
 Pseudo-code:
 
+    dc[16] = [0]*16
     do i = 0 to 15
-        dci <- carry_out(RA[4*i:63] + RB[4*i:63])
-        c <- ([dc[0]]*4 || [dc[1]]*4 || [dc[2]]*4 || [dc[3]]*4 ||
-              [dc[4]]*4 || [dc[5]]*4 || [dc[6]]*4 || [dc[7]]*4 ||
-              [dc[8]]*4 || [dc[9]]*4 || [dc[10]]*4 || [dc[11]]*4 ||
-              [dc[12]]*4 || [dc[13]]*4 || [dc[14]]*4 || [dc[15]]*4)
-        RT <- (¬c) & 0x6666_6666_6666_6666
+        temp <- (0b0 || RA[4*i:63]) + (0b0 || RB[4*i:63])
+        dc[i] <- temp[0]
+    c <- ([dc[0]]*4 || [dc[1]]*4 || [dc[2]]*4 || [dc[3]]*4 ||
+            [dc[4]]*4 || [dc[5]]*4 || [dc[6]]*4 || [dc[7]]*4 ||
+            [dc[8]]*4 || [dc[9]]*4 || [dc[10]]*4 || [dc[11]]*4 ||
+            [dc[12]]*4 || [dc[13]]*4 || [dc[14]]*4 || [dc[15]]*4)
+    RT <- (¬c) & 0x6666_6666_6666_6666
 
 Special Registers Altered: