On Mon, May 01, 2006 at 08:42:08PM +0200, Stefan Weil wrote:
> >- if (((tmp ^ T1 ^ (-1)) & (T0 ^ T1)) >> 31) {
> >+ if (~(T0 ^ T1) & (T0 ^ tmp) & 0x80000000) {> Hello Dirk, > > which additions / subtractions are handled incorrectly by the current code? > Here is the result of a test which shows that the current code (which is > based on my patch) > raises an exception for 0x80000000 + 0x80000000. > > Daniel, perhaps you could sent the code you used to check overflow > conditions? I used GDB. (gdb) set $T0 = 0x80000000 (gdb) set $T1 = 0x80000000 (gdb) set $tmp = $T0 + $T1 (gdb) p (($tmp ^ $T1 ^ (-1)) & ($T0 ^ $T1)) >> 31 $1 = 0 I see no reason why it should be wrong. $tmp is of course zero. The high bit of tmp is not the same as the high bit of T1, therefore $tmp ^ $T1 ^ (-1) == 0. Therefore the if is false. I even compiled and ran the sample -> no exception. Oh, damn! tmp is not the result, T0 is the result. No wonder this didn't make any sense. I apologize, I'm really batting zero today. -- Daniel Jacobowitz CodeSourcery _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
