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Tue, 25 Feb 2025 05:29:51 -0800 (PST) Received: from visitorckw-System-Product-Name ([140.113.216.168]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2fceb02d51fsm8424850a91.2.2025.02.25.05.29.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Feb 2025 05:29:50 -0800 (PST) Date: Tue, 25 Feb 2025 21:29:40 +0800 From: Kuan-Wei Chiu To: Yury Norov Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, jk@ozlabs.org, joel@jms.id.au, eajames@linux.ibm.com, andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, dmitry.torokhov@gmail.com, mchehab@kernel.org, awalls@md.metrocast.net, hverkuil@xs4all.nl, miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com, louis.peens@corigine.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, parthiban.veerasooran@microchip.com, arend.vanspriel@broadcom.com, johannes@sipsolutions.net, gregkh@linuxfoundation.org, jirislaby@kernel.org, akpm@linux-foundation.org, hpa@zytor.com, alistair@popple.id.au, linux@rasmusvillemoes.dk, Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-fsi@lists.ozlabs.org, dri-devel@lists.freedesktop.org, linux-input@vger.kernel.org, linux-media@vger.kernel.org, linux-mtd@lists.infradead.org, oss-drivers@corigine.com, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, brcm80211@lists.linux.dev, brcm80211-dev-list.pdl@broadcom.com, linux-serial@vger.kernel.org, bpf@vger.kernel.org, jserv@ccns.ncku.edu.tw, Yu-Chun Lin Subject: Re: [PATCH 02/17] bitops: Add generic parity calculation for u64 Message-ID: References: <20250223164217.2139331-1-visitorckw@gmail.com> <20250223164217.2139331-3-visitorckw@gmail.com> Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Yury, On Mon, Feb 24, 2025 at 02:27:03PM -0500, Yury Norov wrote: > On Mon, Feb 24, 2025 at 12:42:02AM +0800, Kuan-Wei Chiu wrote: > > Several parts of the kernel open-code parity calculations using > > different methods. Add a generic parity64() helper implemented with the > > same efficient approach as parity8(). > > No reason to add parity32() and parity64() in separate patches Ack. > > > Co-developed-by: Yu-Chun Lin > > Signed-off-by: Yu-Chun Lin > > Signed-off-by: Kuan-Wei Chiu > > --- > > include/linux/bitops.h | 22 ++++++++++++++++++++++ > > 1 file changed, 22 insertions(+) > > > > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > > index fb13dedad7aa..67677057f5e2 100644 > > --- a/include/linux/bitops.h > > +++ b/include/linux/bitops.h > > @@ -281,6 +281,28 @@ static inline int parity32(u32 val) > > return (0x6996 >> (val & 0xf)) & 1; > > } > > > > +/** > > + * parity64 - get the parity of an u64 value > > + * @value: the value to be examined > > + * > > + * Determine the parity of the u64 argument. > > + * > > + * Returns: > > + * 0 for even parity, 1 for odd parity > > + */ > > +static inline int parity64(u64 val) > > +{ > > + /* > > + * One explanation of this algorithm: > > + * https://funloop.org/codex/problem/parity/README.html > > This is already referenced in sources. No need to spread it for more. Ack. > > > + */ > > + val ^= val >> 32; > > + val ^= val >> 16; > > + val ^= val >> 8; > > + val ^= val >> 4; > > + return (0x6996 >> (val & 0xf)) & 1; > > It's better to avoid duplicating the same logic again and again. Ack. > > > +} > > + > > So maybe make it a macro? > > > From f17a28ae3429f49825d65ebc0f7717c6a191a3e2 Mon Sep 17 00:00:00 2001 > From: Yury Norov > Date: Mon, 24 Feb 2025 14:14:27 -0500 > Subject: [PATCH] bitops: generalize parity8() > > The generic parity calculation approach may be easily generalized for > other standard types. Do that and drop sub-optimal implementation of > parity calculation in x86 code. > > Signed-off-by: Yury Norov [NVIDIA] > --- > arch/x86/kernel/bootflag.c | 14 +----------- > include/linux/bitops.h | 47 +++++++++++++++++++++++++++----------- > 2 files changed, 35 insertions(+), 26 deletions(-) > > diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c > index 3fed7ae58b60..4a85c69a28f8 100644 > --- a/arch/x86/kernel/bootflag.c > +++ b/arch/x86/kernel/bootflag.c > @@ -2,6 +2,7 @@ > /* > * Implement 'Simple Boot Flag Specification 2.0' > */ > +#include > #include > #include > #include > @@ -20,19 +21,6 @@ > > int sbf_port __initdata = -1; /* set via acpi_boot_init() */ > > -static int __init parity(u8 v) > -{ > - int x = 0; > - int i; > - > - for (i = 0; i < 8; i++) { > - x ^= (v & 1); > - v >>= 1; > - } > - > - return x; > -} > - > static void __init sbf_write(u8 v) > { > unsigned long flags; > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index c1cb53cf2f0f..29601434f5f4 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -230,10 +230,10 @@ static inline int get_count_order_long(unsigned long l) > } > > /** > - * parity8 - get the parity of an u8 value > + * parity - get the parity of a value > * @value: the value to be examined > * > - * Determine the parity of the u8 argument. > + * Determine parity of the argument. > * > * Returns: > * 0 for even parity, 1 for odd parity > @@ -241,24 +241,45 @@ static inline int get_count_order_long(unsigned long l) > * Note: This function informs you about the current parity. Example to bail > * out when parity is odd: > * > - * if (parity8(val) == 1) > + * if (parity(val) == 1) > * return -EBADMSG; > * > * If you need to calculate a parity bit, you need to draw the conclusion from > * this result yourself. Example to enforce odd parity, parity bit is bit 7: > * > - * if (parity8(val) == 0) > + * if (parity(val) == 0) > * val ^= BIT(7); > + * > + * One explanation of this algorithm: > + * https://funloop.org/codex/problem/parity/README.html > */ > -static inline 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; > -} > +#define parity(val) \ > +({ \ > + u64 __v = (val); \ > + int __ret; \ > + switch (BITS_PER_TYPE(val)) { \ > + case 64: \ > + __v ^= __v >> 32; \ > + fallthrough; \ > + case 32: \ > + __v ^= __v >> 16; \ > + fallthrough; \ > + case 16: \ > + __v ^= __v >> 8; \ > + fallthrough; \ > + case 8: \ > + __v ^= __v >> 4; \ > + __ret = (0x6996 >> (__v & 0xf)) & 1; \ > + break; \ > + default: \ > + BUILD_BUG(); \ > + } \ > + __ret; \ > +}) > + > +#define parity8(val) parity((u8)(val)) > +#define parity32(val) parity((u32)(val)) > +#define parity64(val) parity((u64)(val)) > What do you think about using these inline functions instead of macros? Except for parity8(), each function is a single line and follows the same logic. I find inline functions more readable, and coding-style.rst also recommends them over macros. Regards, Kuan-Wei diff --git a/include/linux/bitops.h b/include/linux/bitops.h index c1cb53cf2f0f..d518a382f1fe 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -260,6 +260,26 @@ static inline int parity8(u8 val) return (0x6996 >> (val & 0xf)) & 1; } +static inline parity16(u16 val) +{ + return parity8(val ^ (val >> 8)); +} + +static inline parity16(u16 val) +{ + return parity8(val ^ (val >> 8)); +} + +static inline parity32(u32) +{ + return parity16(val ^ (val >> 16)); +} + +static inline parity64(u64) +{ + return parity32(val ^ (val >> 32)); +} + /** * __ffs64 - find first set bit in a 64 bit word * @word: The 64 bit word > /** > * __ffs64 - find first set bit in a 64 bit word > -- > 2.43.0 >