From: David Laight <david.laight.linux@gmail.com>
To: David Desobry <david.desobry@formalgen.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
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
Date: Wed, 21 Jan 2026 09:54:05 +0000 [thread overview]
Message-ID: <20260121095405.58fa513f@pumpkin> (raw)
In-Reply-To: <ef852c16-3736-4bd5-bc65-69211b05506e@formalgen.com>
On Wed, 21 Jan 2026 01:04:39 +0100
David Desobry <david.desobry@formalgen.com> 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
next prev parent reply other threads:[~2026-01-21 9:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-20 17:47 [PATCH v2] x86/lib: Optimize num_digits() and fix INT_MIN overflow David Desobry
2026-01-20 18:03 ` H. Peter Anvin
2026-01-20 21:46 ` David Laight
2026-01-20 23:19 ` [PATCH v3] " David Desobry
2026-01-20 23:32 ` [PATCH v2] " David Desobry
2026-01-20 23:49 ` H. Peter Anvin
2026-01-21 0:04 ` David Desobry
2026-01-21 0:17 ` H. Peter Anvin
2026-01-21 9:39 ` [PATCH v4] " David Desobry
2026-01-21 11:36 ` David Laight
2026-01-21 15:46 ` H. Peter Anvin
2026-01-21 9:54 ` David Laight [this message]
2026-01-21 10:32 ` [PATCH v5] x86/lib: Rename num_digits() to num_digits_u32() and optimize David Desobry
2026-01-21 10:40 ` [PATCH v2] x86/lib: Optimize num_digits() and fix INT_MIN overflow David Desobry
2026-01-21 11:51 ` Maciej W. Rozycki
2026-01-23 7:06 ` H. Peter Anvin
2026-01-23 10:55 ` Maciej W. Rozycki
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