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Message-ID: <e00be589-4e9e-48ec-8a25-ad7460f304fa@roeck-us.net>
Date: Thu, 22 Feb 2024 08:04:49 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
Helge Deller <deller@....de>, Arnd Bergmann <arnd@...db.de>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org
Subject: Re: [PATCH 4/4] parisc: checksum: Optimize from32to16
On Wed, Feb 21, 2024 at 06:37:14PM -0800, Charlie Jenkins wrote:
> Replace the shifting and masking of x with a rotation. This generates
> better assembly.
>
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
Tested-by: Guenter Roeck <linux@...ck-us.net>
> ---
> arch/parisc/lib/checksum.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/arch/parisc/lib/checksum.c b/arch/parisc/lib/checksum.c
> index eaa660491e24..1ae8cc730d13 100644
> --- a/arch/parisc/lib/checksum.c
> +++ b/arch/parisc/lib/checksum.c
> @@ -27,11 +27,8 @@
>
> static inline unsigned short from32to16(unsigned int x)
> {
> - /* 32 bits --> 16 bits + carry */
> - x = (x & 0xffff) + (x >> 16);
> - /* 16 bits + carry --> 16 bits including carry */
> - x = (x & 0xffff) + (x >> 16);
> - return (unsigned short)x;
> + x += ror32(x, 16);
> + return (unsigned short)(x >> 16);
> }
>
> unsigned int do_csum(const unsigned char *buff, int len)
>
> --
> 2.34.1
>
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