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Date: Sun, 18 Oct 2009 16:29:00 +0200
Message-ID: <761ea48b0910180729s1221bf45m4c38303ca2f44657@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH] target-arm: fix sdiv helper
From: Laurent Desnogues <laurent.desnogues@gmail.com>
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org

On Thu, Oct 15, 2009 at 11:08 PM, Aurelien Jarno <aurelien@aurel32.net> wro=
te:
> (INT32_MIN / -1) triggers an overflow, and the result depends on the
> host architecture (INT32_MIN on arm, -1 on ppc, SIGFPE on x86). Use a
> test to output the correct value.
>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
> =A0target-arm/helper.c | =A0 =A02 ++
> =A01 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 701629a..b3d6198 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -404,6 +404,8 @@ int32_t HELPER(sdiv)(int32_t num, int32_t den)
> =A0{
> =A0 =A0 if (den =3D=3D 0)
> =A0 =A0 =A0 return 0;
> + =A0 =A0if (num =3D=3D INT_MIN && den =3D=3D -1)
> + =A0 =A0 =A0return INT_MIN;
> =A0 =A0 return num / den;
> =A0}
>
> --
> 1.6.1.3

Acked-by: Laurent Desnogues <laurent.desnogues@gmail.com>

That is provided we accept the behaviour for division by zero is
not strictly conforming to what the ARM ARM says.

Also note this instruction is not available on v7-A CPU's (Cortex-A8
for instance).  It's part of v7-R (Cortex R4).


Laurent