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[2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432dd78f5a8sm3131139f8f.27.2026.01.09.08.41.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Jan 2026 08:41:36 -0800 (PST) From: Petr Tesarik To: Yury Norov , Rasmus Villemoes Cc: Richard Henderson , Matt Turner , Magnus Lindholm , Vineet Gupta , Geert Uytterhoeven , "Maciej W. Rozycki" , Thomas Bogendoerfer , Madhavan Srinivasan , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Chris Zankel , Max Filippov , Patrik Jakobsson , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Robin Murphy , Joerg Roedel , Will Deacon , Jakub Kicinski , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , Oliver Neukum , Arnd Bergmann , Kuan-Wei Chiu , Andrew Morton , Marcel Holtmann , Johan Hedberg , Luiz Augusto von Dentz , Pablo Neira Ayuso , Florian Westphal , linux-kernel@vger.kernel.org, Petr Tesarik Subject: [RFC PATCH 0/2] Helper to isolate least-significant bit Date: Fri, 9 Jan 2026 17:41:34 +0100 Message-ID: X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Isolation of the least significant bit can be achieved with 3 basic ALU operations which are already open-coded in various places in the kernel. However, since other places less efficient constructs, for example `1UL << ffs(x)`, I assume the trick is known only to some authors, and it's worth adding a helper to promote its use. Petr Tesarik (2): bits: introduce ffs_val() treewide, bits: use ffs_val() where it is open-coded arch/alpha/include/asm/bitops.h | 2 +- arch/alpha/kernel/core_cia.c | 2 +- arch/alpha/kernel/smp.c | 2 +- arch/arc/include/asm/bitops.h | 2 +- arch/m68k/include/asm/bitops.h | 12 +++++------ arch/mips/dec/ecc-berr.c | 2 +- arch/mips/include/asm/bitops.h | 4 ++-- arch/mips/pci/pci-malta.c | 4 ++-- arch/powerpc/include/asm/bitops.h | 4 ++-- arch/powerpc/kvm/e500_mmu_host.c | 2 +- arch/powerpc/lib/sstep.c | 2 +- arch/powerpc/xmon/ppc-dis.c | 3 ++- arch/powerpc/xmon/ppc-opc.c | 6 +++--- arch/s390/include/asm/bitops.h | 2 +- arch/xtensa/include/asm/bitops.h | 6 +++--- arch/xtensa/kernel/traps.c | 2 +- drivers/gpu/drm/gma500/psb_intel_sdvo.c | 2 +- drivers/iommu/dma-iommu.c | 2 +- drivers/net/ethernet/netronome/nfp/bpf/jit.c | 2 +- drivers/net/usb/cdc_ncm.c | 4 ++-- include/asm-generic/div64.h | 4 ++-- include/linux/bitfield.h | 3 ++- include/linux/bitops.h | 1 + include/linux/ffs_val.h | 21 ++++++++++++++++++++ include/linux/log2.h | 2 +- include/linux/min_heap.h | 5 +++-- lib/math/gcd.c | 4 ++-- lib/sort.c | 3 ++- net/bluetooth/mgmt.c | 2 +- net/netfilter/nft_set_pipapo.c | 2 +- 30 files changed, 70 insertions(+), 44 deletions(-) create mode 100644 include/linux/ffs_val.h -- 2.52.0