From: Fabrice Bellard <fabrice@bellard.org>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Fix overflow conditions for MIPS add/subtract
Date: Mon, 01 May 2006 21:01:24 +0200 [thread overview]
Message-ID: <44565B04.9070601@bellard.org> (raw)
In-Reply-To: <44563AEC.8070903@gmail.com>
OK. I hope this is correct now :-)
Just a note : there is already a lot of code in QEMU to compute
correctly the overflow and carry flags (for example in the i386
target)... don't spend your time on reinventing them !
Fabrice.
Dirk Behme wrote:
>
> 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);
> }
>
>
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> Qemu-devel mailing list
> Qemu-devel@nongnu.org
> http://lists.nongnu.org/mailman/listinfo/qemu-devel
next prev parent reply other threads:[~2006-05-01 19:02 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-01 16:44 [Qemu-devel] [PATCH] Fix overflow conditions for MIPS add/subtract Dirk Behme
2006-05-01 19:01 ` Fabrice Bellard [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-05-01 18:42 Stefan Weil
2006-05-01 19:18 ` Daniel Jacobowitz
2006-05-01 21:40 ` Fabrice Bellard
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