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[216.228.125.128]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2230a092fc9sm1130585ad.126.2025.02.24.14.30.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2025 14:30:10 -0800 (PST) Date: Mon, 24 Feb 2025 17:30:08 -0500 From: Yury Norov To: "H. Peter Anvin" Cc: Uros Bizjak , Kuan-Wei Chiu , tglx@linutronix.de, Ingo Molnar , 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, mingo@kernel.org, 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 03/17] x86: Replace open-coded parity calculation with parity8() Message-ID: References: <20250223164217.2139331-1-visitorckw@gmail.com> <20250223164217.2139331-4-visitorckw@gmail.com> <68F1ED19-B0C2-4E78-B504-2F7C040ACC0A@zytor.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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <68F1ED19-B0C2-4E78-B504-2F7C040ACC0A@zytor.com> On Mon, Feb 24, 2025 at 02:21:13PM -0800, H. Peter Anvin wrote: > On February 24, 2025 2:17:29 PM PST, Yury Norov wrote: > >On Mon, Feb 24, 2025 at 01:55:28PM -0800, H. Peter Anvin wrote: > >> On 2/24/25 07:24, Uros Bizjak wrote: > >> > > >> > > >> > On 23. 02. 25 17:42, Kuan-Wei Chiu wrote: > >> > > Refactor parity calculations to use the standard parity8() helper. This > >> > > change eliminates redundant implementations and improves code > >> > > efficiency. > >> > > >> > The patch improves parity assembly code in bootflag.o from: > >> > > >> >   58:    89 de                    mov    %ebx,%esi > >> >   5a:    b9 08 00 00 00           mov    $0x8,%ecx > >> >   5f:    31 d2                    xor    %edx,%edx > >> >   61:    89 f0                    mov    %esi,%eax > >> >   63:    89 d7                    mov    %edx,%edi > >> >   65:    40 d0 ee                 shr    %sil > >> >   68:    83 e0 01                 and    $0x1,%eax > >> >   6b:    31 c2                    xor    %eax,%edx > >> >   6d:    83 e9 01                 sub    $0x1,%ecx > >> >   70:    75 ef                    jne    61 > >> >   72:    39 c7                    cmp    %eax,%edi > >> >   74:    74 7f                    je     f5 > >> >   76: > >> > > >> > to: > >> > > >> >   54:    89 d8                    mov    %ebx,%eax > >> >   56:    ba 96 69 00 00           mov    $0x6996,%edx > >> >   5b:    c0 e8 04                 shr    $0x4,%al > >> >   5e:    31 d8                    xor    %ebx,%eax > >> >   60:    83 e0 0f                 and    $0xf,%eax > >> >   63:    0f a3 c2                 bt     %eax,%edx > >> >   66:    73 64                    jae    cc > >> >   68: > >> > > >> > which is faster and smaller (-10 bytes) code. > >> > > >> > >> Of course, on x86, parity8() and parity16() can be implemented very simply: > >> > >> (Also, the parity functions really ought to return bool, and be flagged > >> __attribute_const__.) > > > >There was a discussion regarding return type when parity8() was added. > >The integer type was taken over bool with a sort of consideration that > >bool should be returned as an answer to some question, like parity_odd(). > > > >To me it's not a big deal. We can switch to boolean and describe in > >comment what the 'true' means for the parity() function. > > Bool is really the single-bit type, and gives the compiler more information. You could argue that the function really should be called parity_odd*() in general, but that's kind of excessive IMO. Yes, I could, but I will not. :) I also feel like bool looks more natural here.