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From: Willy Tarreau <w@1wt.eu>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tools/nolibc/string: fix memcmp() implementation
Date: Thu, 13 Oct 2022 08:56:03 +0200	[thread overview]
Message-ID: <20221013065603.GB16609@1wt.eu> (raw)
In-Reply-To: <20221010113606.2329457-1-linux@rasmusvillemoes.dk>

Hi Rasmus,

On Mon, Oct 10, 2022 at 01:36:06PM +0200, Rasmus Villemoes wrote:
> The C standard says that memcmp() must treat the buffers as consisting
> of "unsigned chars". If char happens to be unsigned, the casts are ok,
> but then obviously the c1 variable can never contain a negative
> value. And when char is signed, the casts are wrong, and there's still
> a problem with using an 8-bit quantity to hold the difference, because
> that can range from -255 to +255.
> 
> For example, assuming char is signed, comparing two 1-byte buffers,
> one containing 0x00 and another 0x80, the current implementation would
> return -128 for both memcmp(a, b, 1) and memcmp(b, a, 1), whereas one
> of those should of course return something positive.

You're totally right of course, thank you for spotting this one! I'm
queuing it now.

Regards,
Willy

  reply	other threads:[~2022-10-13  6:56 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-10 11:36 [PATCH] tools/nolibc/string: fix memcmp() implementation Rasmus Villemoes
2022-10-13  6:56 ` Willy Tarreau [this message]
2022-10-21  6:01 Willy Tarreau

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