From: lkcl <lkcl@web>
Date: Fri, 9 Jun 2023 12:01:55 +0000 (+0100)
Subject: (no commit message)
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=0c21d3ebd418b275f18c2ad7b36160987e44f55b;p=libreriscv.git

---

diff --git a/openpower/sv/po9_encoding/discussion.mdwn b/openpower/sv/po9_encoding/discussion.mdwn
index da92f8043..67df273a7 100644
--- a/openpower/sv/po9_encoding/discussion.mdwn
+++ b/openpower/sv/po9_encoding/discussion.mdwn
@@ -149,24 +149,51 @@ EXT200-231:
 EXT900:
 
 ```
+    # easy first step
     if not PO9                 return False
-    if Word[30:31] != 0b00     return False
-    if Word[62]    =  0b1      return False
-    if Word[62:63] =  0b00 and
+    # eliminate EXT0xx, 32-Unvec-in-64b
+    if Word[31] = 0b1          return False
+    # eliminate EXT2xx
+    if Word[30:31] =  0b10 and
+       Word[33:37] != 0b10001   return False
+    # eliminate currently-RESERVED areas
+    if Word[30:31] =  0b10 and
+       Word[62]    =  0b1      return False
+    # eliminate final RESERVED area
+    if Word[30:31] =  0b10 and
+       Word[62:63] =  0b00 and
        Word[6:29 ] =  0x000000 return False
+    # last-remaining is EXT900
     return True
 ```
 
-EXT000-063:
+**EXT000-063**: (includes Prefixed)
 
 ```
     if PO1                     return False # or other reserved
-    if not PO9                 return False
+    if not PO9                 return True  # prefixed needs more
+    # eliminate EXT900
     if Word[30:31] =  0b00     return False
+    # eliminate Prefixed-EXT900, RESERVED and EXT200
     if Word[31]    =  0b0      return False
+    # eliminate 32-bit Unvec in 64b area
     if Word[30:31] =  0b01 and
        Word[6:29 ] =  0x000000 return False
     return True
 ```
 
+**SVP64**:
 
+```
+    # easy-elimination, first
+    if Word[30]    =  0b0      return False
+    if not PO9                 return False
+    # eliminate anything not SVP64:EXT900
+    if Word[30:31] =  0b10 and
+       Word[33:37] = 0b10001 and
+       Word[62:63] != 0b01    return False
+    # eliminate anything not SVP64:EXT200-231
+    if Word[31:32] =  0b00    return False
+    # all remaining combinations are SVP64:EXTnnn
+    return True
+```