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Re: [PATCH] x86: do away with HAVE_AS_NEGATIVE_TRUE
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 17 May 2023 18:05:03 +0100
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- Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17/05/2023 3:22 pm, Jan Beulich wrote:
> There's no real need for the associated probing - we can easily convert
> to a uniform value without knowing the specific behavior (note also that
> the respective comments weren't fully correct and have gone stale). All
> we (need to) depend upon is unary ! producing 0 or 1 (and never -1).
>
> For all present purposes yielding a value with all bits set is more
> useful.
>
> No difference in generated code.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Unlike in C, there's also binary ! in assembly expressions, and even
> binary !!. But those don't get in the way here.
I had been wanting to do this for a while, but IMO a clearer expression
is to take ((x) & 1) to discard the sign.
It doesn't change any of the logic to use +1 (I don't think), and it's
definitely the more common way for the programmer to think.
~Andrew
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