linux-kernel - Re: [PATCH] tile: optimize strnlen using SIMD instructions

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Message-ID: <CAMo8BfJEG1L125+pTq3Ke0mD__gm8u7mqJxUf9UkPXLpjBgrUg@mail.gmail.com>
Date:	Fri, 2 Aug 2013 00:42:48 +0400
From:	Max Filippov <jcmvbkbc@...il.com>
To:	Ken Steele <ken@...era.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tile: optimize strnlen using SIMD instructions

Hi Ken,

On Thu, Aug 1, 2013 at 11:55 PM, Ken Steele <ken@...era.com> wrote:
> +       /* Read the first word, but force bytes before the string to be nonzero.
> +        * This expression works because we know shift counts are taken mod 32.
> +        */
> +       v = *p | ((1 << (s_int << 3)) - 1);

This expression potentially has undefined behaviour according to C99, 6.5.7:3.
IOW it may work, but it doesn't always have to.

-- 
Thanks.
-- Max
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