[Qemu-devel] [PATCH] Fix test for two's complement overflow

[Ralf Baechle <ralf@linux-mips.org>]

Hi Fabrice,

A sequence like

	addiu	$r0, $r0, 1
	addi	$r0, $r0, -1

would result in an integer overflow exception on MIPS targets.

This test fixes the test for a signed overflow done by the add, addi,
sub and subi instructions.

 target-mips/op.c |   18 +++++++++---------
 1 files changed, 9 insertions(+), 9 deletions(-)

--- suckage/target-mips/op.c 5 Dec 2005 19:59:36 -0000
+++ suckage/target-mips/op.c 15 Feb 2006 16:15:45 -0000
@@ -202,13 +202,13 @@
 
 void op_addo (void)
 {
-    target_ulong tmp;
+    uint64_t tmp;
 
-    tmp = T0;
-    T0 += T1;
-    if ((T0 >> 31) ^ (T1 >> 31) ^ (tmp >> 31)) {
+    tmp = (int64_t) (int32_t) T0 + (int64_t) (int32_t) T1;
+    if (((tmp >> 32) ^ (tmp >> 31)) & 1)
         CALL_FROM_TB1(do_raise_exception_direct, EXCP_OVERFLOW);
-    }
+
+    T0 = tmp;
     RETURN();
 }
 
@@ -222,11 +222,11 @@
 {
     target_ulong tmp;
 
-    tmp = T0;
-    T0 = (int32_t)T0 - (int32_t)T1;
-    if (!((T0 >> 31) ^ (T1 >> 31) ^ (tmp >> 31))) {
+    tmp = (int64_t) (int32_t) T0 - (int64_t) (int32_t) T1;
+    if (((tmp >> 32) ^ (tmp >> 31)) & 1)
         CALL_FROM_TB1(do_raise_exception_direct, EXCP_OVERFLOW);
-    }
+
+    T0 = tmp;
     RETURN();
 }