From 76e050c2e62995f1d6905e28674dea3a7fcff1a5 Mon Sep 17 00:00:00 2001
From: bellard <bellard@c046a42c-6fe2-441c-8c8c-71466251a162>
Date: Sun, 23 Apr 2006 15:18:58 +0000
Subject: [PATCH] Fix overflow conditions for MIPS add / subtract (Stefan Weil)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@1828 c046a42c-6fe2-441c-8c8c-71466251a162
---
 target-mips/op.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/target-mips/op.c b/target-mips/op.c
index 71abd95bea..e0d3463be1 100644
--- a/target-mips/op.c
+++ b/target-mips/op.c
@@ -206,7 +206,8 @@ void op_addo (void)
 
     tmp = T0;
     T0 += T1;
-    if ((T0 >> 31) ^ (T1 >> 31) ^ (tmp >> 31)) {
+    if (((tmp ^ T1 ^ (-1)) & (T0 ^ T1)) >> 31) {
+       /* operands of same sign, result different sign */
         CALL_FROM_TB1(do_raise_exception_direct, EXCP_OVERFLOW);
     }
     RETURN();
@@ -224,7 +225,8 @@ void op_subo (void)
 
     tmp = T0;
     T0 = (int32_t)T0 - (int32_t)T1;
-    if (!((T0 >> 31) ^ (T1 >> 31) ^ (tmp >> 31))) {
+    if (((tmp ^ T1) & (tmp ^ T0)) >> 31) {
+       /* operands of different sign, first operand and result different sign */
         CALL_FROM_TB1(do_raise_exception_direct, EXCP_OVERFLOW);
     }
     RETURN();
-- 
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