Received-SPF: pass (google.com: domain of linux-kernel+bounces-75804-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
From: Charlie Jenkins <charlie@rivosinc.com>
Date: Wed, 21 Feb 2024 18:37:14 -0800
Subject: [PATCH 4/4] parisc: checksum: Optimize from32to16
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Message-Id: <20240221-parisc_use_generic_checksum-v1-4-ad34d895fd1b@rivosinc.com>
References: <20240221-parisc_use_generic_checksum-v1-0-ad34d895fd1b@rivosinc.com>
In-Reply-To: <20240221-parisc_use_generic_checksum-v1-0-ad34d895fd1b@rivosinc.com>
To: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, 
 Helge Deller <deller@gmx.de>, Arnd Bergmann <arnd@arndb.de>, 
 Andrew Morton <akpm@linux-foundation.org>, 
 Guenter Roeck <linux@roeck-us.net>
Cc: linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, 
 linux-arch@vger.kernel.org, Charlie Jenkins <charlie@rivosinc.com>

Replace the shifting and masking of x with a rotation. This generates
better assembly.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
 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