From: Paolo Bonzini <pbonzini@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
Alex Williamson <alex.williamson@redhat.com>,
QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH v2 1/3] int128: add int128_exts64()
Date: Thu, 22 Aug 2013 11:48:48 +0200 [thread overview]
Message-ID: <5215DE80.4030203@redhat.com> (raw)
In-Reply-To: <CAFEAcA_WDhmGLpzo=+sodS+ZwTW-Kb-U9jw4SP3Sjz0P3Ds+1w@mail.gmail.com>
Il 22/08/2013 11:47, Peter Maydell ha scritto:
> On 22 August 2013 10:09, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 22/08/2013 10:20, Alexey Kardashevskiy ha scritto:
>>> +static inline Int128 int128_exts64(int64_t a)
>>> +{
>>> + return (Int128) { .lo = a, .hi = (a >> 63) ? -1 : 0 };
>>> +}
>>
>> The "? -1 : 0" is not necessary, but the compiler will remove it at -O1
>> or more (interestingly, or -O0 it will remove the shift and leave the
>> conditional!).
>
> We can avoid relying on implementation defined
> behaviour here by using
> .hi = (a < 0) ? -1 : 0;
>
> (I know we allow ourselves to assume right-shift of signed
> ints is arithmetic shift, but I think it's nicer to avoid it unless
> it really makes the code better.)
This is what Alexey proposed. I suggested (a >> 63) without the ?: but
he misunderstood my (probably not clear enough) suggestion.
Paolo
next prev parent reply other threads:[~2013-08-22 9:49 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-22 8:20 [Qemu-devel] [PATCH v2 0/3] vfio: fixes for better support for 128 bit memory section sizes Alexey Kardashevskiy
2013-08-22 8:20 ` [Qemu-devel] [PATCH v2 1/3] int128: add int128_exts64() Alexey Kardashevskiy
2013-08-22 9:09 ` Paolo Bonzini
2013-08-22 9:47 ` Peter Maydell
2013-08-22 9:48 ` Paolo Bonzini [this message]
2013-08-22 10:43 ` Peter Maydell
2013-08-22 10:50 ` Alexey Kardashevskiy
2013-08-22 11:14 ` Paolo Bonzini
2013-08-22 8:20 ` [Qemu-devel] [PATCH v2 2/3] vfio: Fix debug output for int128 values Alexey Kardashevskiy
2013-08-22 8:20 ` [Qemu-devel] [PATCH v2 3/3] vfio: Fix 128 bit handling Alexey Kardashevskiy
2013-08-22 9:11 ` Paolo Bonzini
2013-08-22 10:41 ` Alexey Kardashevskiy
2013-08-22 11:13 ` Paolo Bonzini
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