From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Sat, 11 Jul 2020 10:23:45 +0000 (+0100)
Subject: overflow test MSBs not LSBs
X-Git-Tag: convert-csv-opcode-to-binary~2368
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=b3588e5696c11ad427a9f359777a5eb4f5183903;p=libreriscv.git

overflow test MSBs not LSBs
---

diff --git a/openpower/isa/fixedarith.mdwn b/openpower/isa/fixedarith.mdwn
index 75bf9faa0..1931c72ec 100644
--- a/openpower/isa/fixedarith.mdwn
+++ b/openpower/isa/fixedarith.mdwn
@@ -350,8 +350,8 @@ Pseudo-code:
 
     prod[0:63] <- MULS((RA)[32:63], (RB)[32:63])
     RT <- prod
-    overflow <- ((prod[32:63] != 0x0000_0000) &
-                 (prod[32:63] != 0xffff_ffff))
+    overflow <- ((prod[0:31] != 0x0000_0000) &
+                 (prod[0:31] != 0xffff_ffff))
 
 Special Registers Altered:
 
@@ -564,6 +564,8 @@ Pseudo-code:
 
     prod[0:127] <- MULS((RA), (RB))
     RT <- prod[64:127]
+    overflow <- ((prod[0:63] != 0x0000_0000_0000_0000) &
+                 (prod[0:63] != 0xffff_ffff_ffff_ffff))
 
 Special Registers Altered: