linux-kernel - Re: [PATCH] minmax: clamp more efficiently by avoiding extra comparison

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Message-ID: <Yy2MDWCHTW0M3Z6i@smile.fi.intel.com>
Date:   Fri, 23 Sep 2022 13:35:57 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] minmax: clamp more efficiently by avoiding extra
 comparison

On Fri, Sep 23, 2022 at 12:06:21PM +0200, Jason A. Donenfeld wrote:
> Currently the clamp algorithm does:
> 
> 	if (val > hi)
> 		val = hi;
> 	if (val < lo)
> 		val = lo;
> 
> But since hi > lo by definition, this can be made more efficient with:

It's strongly speaking, but we have to proof that, right?
So, while I haven't checked the code, this change should also
include (does it?) the corresponding compile-time checks (for
constant arguments) in similar way how it's done for GENMASK().

Otherwise I have no objections.

> 	if (val > hi)
> 		val = hi;
> 	else if (val < lo)
> 		val = lo;
> 
> So fix up the clamp and clamp_t functions to do this, adding the same
> argument checking as for min and min_t.

-- 
With Best Regards,
Andy Shevchenko