linux-kernel - [PATCH v2 02/18] bitops: Optimize parity8() using __builtin

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20250301142409.2513835-3-visitorckw@gmail.com>
Date: Sat,  1 Mar 2025 22:23:53 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	jk@...abs.org,
	joel@....id.au,
	eajames@...ux.ibm.com,
	andrzej.hajda@...el.com,
	neil.armstrong@...aro.org,
	rfoss@...nel.org,
	maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org,
	tzimmermann@...e.de,
	airlied@...il.com,
	simona@...ll.ch,
	dmitry.torokhov@...il.com,
	mchehab@...nel.org,
	awalls@...metrocast.net,
	hverkuil@...all.nl,
	miquel.raynal@...tlin.com,
	richard@....at,
	vigneshr@...com,
	louis.peens@...igine.com,
	andrew+netdev@...n.ch,
	davem@...emloft.net,
	edumazet@...gle.com,
	pabeni@...hat.com,
	parthiban.veerasooran@...rochip.com,
	arend.vanspriel@...adcom.com,
	johannes@...solutions.net,
	gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	yury.norov@...il.com,
	akpm@...ux-foundation.org
Cc: hpa@...or.com,
	alistair@...ple.id.au,
	linux@...musvillemoes.dk,
	Laurent.pinchart@...asonboard.com,
	jonas@...boo.se,
	jernej.skrabec@...il.com,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	linux-fsi@...ts.ozlabs.org,
	dri-devel@...ts.freedesktop.org,
	linux-input@...r.kernel.org,
	linux-media@...r.kernel.org,
	linux-mtd@...ts.infradead.org,
	oss-drivers@...igine.com,
	netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org,
	brcm80211@...ts.linux.dev,
	brcm80211-dev-list.pdl@...adcom.com,
	linux-serial@...r.kernel.org,
	bpf@...r.kernel.org,
	jserv@...s.ncku.edu.tw,
	david.laight.linux@...il.com,
	andrew.cooper3@...rix.com,
	Kuan-Wei Chiu <visitorckw@...il.com>,
	Yu-Chun Lin <eleanor15x@...il.com>
Subject: [PATCH v2 02/18] bitops: Optimize parity8() using __builtin_parity()

Refactor parity8() to use __builtin_parity() when no
architecture-specific implementation is available. If the input is a
compile-time constant, expand it using the _parity_const() macro to
enable constant folding, allowing the compiler to optimize it at
compile time.

Additionally, mark parity8() with __attribute_const__ to indicate its
pure nature, ensuring better optimization opportunities.

This change improves efficiency by leveraging compiler intrinsics while
maintaining a fallback mechanism for architectures without specific
implementations.

Co-developed-by: Yu-Chun Lin <eleanor15x@...il.com>
Signed-off-by: Yu-Chun Lin <eleanor15x@...il.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
 include/linux/bitops.h | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index c1cb53cf2f0f..4c307d9c1545 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -229,6 +229,27 @@ static inline int get_count_order_long(unsigned long l)
 	return (int)fls_long(--l);
 }
 
+#define _parity_const(val)	\
+({				\
+	u64 __v = (val);	\
+	int __ret;		\
+	__v ^= __v >> 32;	\
+	__v ^= __v >> 16;	\
+	__v ^= __v >> 8;	\
+	__v ^= __v >> 4;	\
+	__v ^= __v >> 2;	\
+	__v ^= __v >> 1;	\
+	__ret = __v & 1;	\
+	__ret;			\
+})
+
+#ifndef _parity8
+static inline __attribute_const__ int _parity8(u8 val)
+{
+	return __builtin_parity(val);
+}
+#endif
+
 /**
  * parity8 - get the parity of an u8 value
  * @value: the value to be examined
@@ -250,14 +271,9 @@ static inline int get_count_order_long(unsigned long l)
  *	if (parity8(val) == 0)
  *		val ^= BIT(7);
  */
-static inline int parity8(u8 val)
+static inline __attribute_const__ int parity8(u8 val)
 {
-	/*
-	 * One explanation of this algorithm:
-	 * https://funloop.org/codex/problem/parity/README.html
-	 */
-	val ^= val >> 4;
-	return (0x6996 >> (val & 0xf)) & 1;
+	return __builtin_constant_p(val) ? _parity_const(val) : _parity8(val);
 }
 
 /**
-- 
2.34.1