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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4358e24cef3sm10459590f8f.0.2026.01.21.01.54.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Jan 2026 01:54:06 -0800 (PST) Date: Wed, 21 Jan 2026 09:54:05 +0000 From: David Laight To: David Desobry Cc: "H. Peter Anvin" , tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] x86/lib: Optimize num_digits() and fix INT_MIN overflow Message-ID: <20260121095405.58fa513f@pumpkin> In-Reply-To: References: <20260120174748.302078-1-david.desobry@formalgen.com> <20260120214612.73b83cbe@pumpkin> <8923623d-1a23-483d-add7-2fd03a3a2c3d@zytor.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 21 Jan 2026 01:04:39 +0100 David Desobry wrote: > On 1/21/26 00:49, H. Peter Anvin wrote: .. > Actually, the V3 change: > if (val < 0) { > - d++; > - val = -val; > + d = 1; > + v = -val; > + } else { > + d = 0; > + v = val; > } > reintroduced the undefined behavior for val == INT_MIN. > So this V3 version is incorrect. Change to: v = -(val + 1); v++; The compiler notices the two '+ 1' cancel each other out. David > I'm not familiar enough with the rest of the codebase to know if > changing the function signature to unsigned int is correct here. In theory you'd need to change the name and all the callers. David