linux-kernel - Re: [PATCH] fat: Refactor fat_tolower with branchless implementation

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Message-ID: <Z9owx0FbCfc8LHUa@vaxr-BM6660-BM6360>
Date: Wed, 19 Mar 2025 10:49:43 +0800
From: I Hsin Cheng <richard120310@...il.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: hirofumi@...l.parknet.co.jp, linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev,
	jserv@...s.ncku.edu.tw
Subject: Re: [PATCH] fat: Refactor fat_tolower with branchless implementation

On Tue, Mar 18, 2025 at 04:03:23AM +0000, Al Viro wrote:
> On Tue, Mar 18, 2025 at 11:43:09AM +0800, I Hsin Cheng wrote:
> > Elimate the need of if-else branch within fat_tolower, replace it with a
> > branchless bitwise operation. This can reduce the number of branch ~130
> > regarding to the test script[1].
> 
> ... and for values outside of 32..126 it would give wrong results.

Ahh, sorry I didn't take these into consideration, I guess branch is
necessary here then. Thanks for your review!

Best regards,
I Hsin Cheng