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Sender: Richard Henderson <rth7680@gmail.com>
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Date: Sun, 31 Mar 2013 16:19:45 -0700
From: Richard Henderson <rth@twiddle.net>
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Subject: Re: [Qemu-devel] [PATCH] target-ppc: fix nego and subf*o
	instructions
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>

On 2013-03-30 16:54, Aurelien Jarno wrote:
> The overflow computation of nego and subf*o instructions has been broken
> in commit ffe30937. This patch fixes it.
>
> With this change the PPC emulation passes the Gwenole Beauchesne
> testsuite again.
>
> Cc: Alexander Graf <agraf@suse.de>
> Cc: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>   target-ppc/translate.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target-ppc/translate.c b/target-ppc/translate.c
> index 5e741d1..062493a 100644
> --- a/target-ppc/translate.c
> +++ b/target-ppc/translate.c
> @@ -749,7 +749,7 @@ static inline void gen_op_arith_compute_ov(DisasContext *ctx, TCGv arg0,
>       tcg_gen_xor_tl(cpu_ov, arg0, arg1);
>       tcg_gen_xor_tl(t0, arg1, arg2);
>       if (sub) {
> -        tcg_gen_and_tl(cpu_ov, cpu_ov, t0);
> +        tcg_gen_andc_tl(cpu_ov, t0, cpu_ov);
>       } else {
>           tcg_gen_andc_tl(cpu_ov, cpu_ov, t0);
>       }

I'm a bit confused.  This is the exact same algorithm that's used on ARM and 
i386.  And as far as I can determine, all three platforms have the same 
definition of "overflow".


r~