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[216.228.125.128]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2230a01fe28sm1125415ad.100.2025.02.24.14.17.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2025 14:17:31 -0800 (PST) Date: Mon, 24 Feb 2025 17:17:29 -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> Precedence: bulk X-Mailing-List: brcm80211@lists.linux.dev 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: 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.