Re: [Xen-devel] [PATCH v4 05/10] x86: Add functions for 64-bit integer arithmetic

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.01.16 at 22:58, <haozhong.zhang@xxxxxxxxx> wrote:
> This patch adds several functions to take multiplication, division and
> shifting involving 64-bit integers.
> 
> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> ---
> Changes in v4:
>  (addressing Jan Beulich's comments)
>  * Rewrite mul_u64_u64_shr() in assembly.

Thanks, but it puzzles me that the other one didn't get converted
as well. Anyway, I'm not going to make this a requirement, since
at least it appears to match Linux'es variant.

> +static inline u64 mul_u64_u64_shr(u64 a, u64 mul, unsigned int n)
> +{
> +    u64 hi, lo;
> +
> +    asm volatile ( "mulq %2; shrdq %1,%0"
> +                   : "=a" (lo), "=d" (hi)
> +                   : "rm" (mul), "0" (a), "c" (n) );

SHRD formally is a 3-operand instruction, and the fact that gas'
AT&T syntax supports a 2-operand "alias" is, well, odd. Please
let's use the specification mandated 3-operand form properly,
to avoid surprises with e.g. clang.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel