[Qemu-devel] [PATCH] Fix overflow conditions for MIPS add/subtract

[Dirk Behme]

Fix overflow conditions for MIPS add/subtract as proposed by
Daniel Jacobowitz.

http://lists.gnu.org/archive/html/qemu-devel/2006-04/msg00538.html

Regards

Dirk

--- target-mips/op.c_orig       2006-04-30 09:40:46.000000000 +0200
+++ target-mips/op.c    2006-04-30 09:41:52.000000000 +0200
@@ -206,7 +206,7 @@ void op_addo (void)
 
     tmp = T0;
     T0 += T1;
-    if (((tmp ^ T1 ^ (-1)) & (T0 ^ T1)) >> 31) {
+    if (~(T0 ^ T1) & (T0 ^ tmp) & 0x80000000) {
        /* operands of same sign, result different sign */
         CALL_FROM_TB1(do_raise_exception_direct, EXCP_OVERFLOW);
     }
@@ -225,7 +225,7 @@ void op_subo (void)
 
     tmp = T0;
     T0 = (int32_t)T0 - (int32_t)T1;
-    if (((tmp ^ T1) & (tmp ^ T0)) >> 31) {
+    if ((T0 ^ T1) & (T0 ^ tmp) & 0x80000000) {
        /* operands of different sign, first operand and result different sign 
*/
         CALL_FROM_TB1(do_raise_exception_direct, EXCP_OVERFLOW);
     }