From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 15 Jul 2020 14:54:27 +0000 (+0100)
Subject: overflow detection in mullw and mulld off-by-one
X-Git-Tag: convert-csv-opcode-to-binary~2342
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=9ec3591cba034c799df52ffbc3f1dda423bc4f98;p=libreriscv.git

overflow detection in mullw and mulld off-by-one
---

diff --git a/openpower/isa/fixedarith.mdwn b/openpower/isa/fixedarith.mdwn
index 1931c72ec..5f556607e 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[0:31] != 0x0000_0000) &
-                 (prod[0:31] != 0xffff_ffff))
+    overflow <- ((prod[0:32] != 0x0_0000_0000) &
+                 (prod[0:32] != 0x1_ffff_ffff))
 
 Special Registers Altered:
 
@@ -564,8 +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))
+    overflow <- ((prod[0:64] != 0x0_0000_0000_0000_0000) &
+                 (prod[0:64] != 0x1_ffff_ffff_ffff_ffff))
 
 Special Registers Altered: