Re: [PATCH 5/7] xen/bitops: Implement ffs64() in common logic

From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Julien Grall" <julien@xen.org>,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Bertrand Marquis" <bertrand.marquis@arm.com>,
	"Michal Orzel" <michal.orzel@amd.com>,
	"Oleksii Kurochko" <oleksii.kurochko@gmail.com>,
	"Shawn Anastasio" <sanastasio@raptorengineering.com>,
	"consulting @ bugseng . com" <consulting@bugseng.com>,
	"Simone Ballarin" <simone.ballarin@bugseng.com>,
	"Federico Serafini" <federico.serafini@bugseng.com>,
	"Nicola Vetrini" <nicola.vetrini@bugseng.com>,
	Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 5/7] xen/bitops: Implement ffs64() in common logic
Date: Thu, 14 Mar 2024 16:56:07 +0100	[thread overview]
Message-ID: <a103a8cd-33f6-44db-acc0-eb105d86b073@suse.com> (raw)
In-Reply-To: <20240313172716.2325427-6-andrew.cooper3@citrix.com>

On 13.03.2024 18:27, Andrew Cooper wrote:
> --- a/xen/common/bitops.c
> +++ b/xen/common/bitops.c
> @@ -47,6 +47,18 @@ static void test_ffs(void)
>      CHECK(ffsl, 1UL << (BITS_PER_LONG - 1), BITS_PER_LONG);
>      if ( BITS_PER_LONG > 32 )
>          CHECK(ffsl, 1UL << 32, 33);
> +
> +    /*
> +     * unsigned int ffs64(uint64_t)
> +     *
> +     * 32-bit builds of Xen have to split this into two adjacent operations,
> +     * so test all interesting bit positions.
> +     */
> +    CHECK(ffs64, 0, 0);
> +    CHECK(ffs64, 1, 1);
> +    CHECK(ffs64, (uint64_t)0x0000000080000000, 32);
> +    CHECK(ffs64, (uint64_t)0x0000000100000000, 33);
> +    CHECK(ffs64, (uint64_t)0x8000000000000000, 64);

I'm pretty sure Misra will want ULL suffixes on the last two and at least an UL
one on the middle of the lines. The casts aren't going to help (and could then
be dropped).

Jan