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Date: Fri, 14 Mar 2014 15:57:42 +0000
From: "Richard W.M. Jones" <rjones@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] block: Explicitly specify 'unsigned long
 long' for VHDX 64-bit constants
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Kevin Wolf <kwolf@redhat.com>, Jeff Cody <jcody@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>, Alexander Graf <agraf@suse.de>

On Fri, Mar 14, 2014 at 03:38:55PM +0000, Peter Maydell wrote:
> On 14 March 2014 15:36, Richard W.M. Jones <rjones@redhat.com> wrote:
> > On Fri, Mar 14, 2014 at 06:50:37AM -0400, Jeff Cody wrote:
> >> On 32-bit hosts, some compilers will warn on too large integer constants
> >> for constants that are 64-bit in length.  Explicitly put a 'ULL' suffix
> >> on those defines.
> >> -#define VHDX_FILE_SIGNATURE 0x656C696678646876  /* "vhdxfile" in ASCII */
> >> +#define VHDX_FILE_SIGNATURE 0x656C696678646876ULL  /* "vhdxfile" in ASCII */
> >
> > I think it's better to use this C99-defined feature (from <stdint.h>):
> >
> > #define VHDX_FILE_SIGNATURE UINT64_C(0x656C696678646876)
> 
> Why? It's longer and we barely use it anywhere else
> in the codebase, whereas we use the ULL suffix all
> over the place...

It's permitted for unsigned long long to be longer than 64 bits.  The
UINT64_C() macro will always return a 64 bit int constant.  Yup, it's
not likely and for this particular macro it wouldn't matter.  (And I'm
not going to get into language-lawyering ...)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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