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Re: [Qemu-devel] [PATCH v2 1/3] int128: add int128_exts64()
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/3] int128: add int128_exts64() |
Date: |
Thu, 22 Aug 2013 10:47:48 +0100 |
On 22 August 2013 10:09, Paolo Bonzini <address@hidden> 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.)
-- PMM
[Qemu-devel] [PATCH v2 2/3] vfio: Fix debug output for int128 values, Alexey Kardashevskiy, 2013/08/22
[Qemu-devel] [PATCH v2 3/3] vfio: Fix 128 bit handling, Alexey Kardashevskiy, 2013/08/22