From: "Theodore Tso" <tytso@mit.edu>
To: David Laight <david.laight.linux@gmail.com>
Cc: Guan-Chun Wu <409411716@gms.tku.edu.tw>,
Andreas Dilger <adilger.kernel@dilger.ca>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
visitorckw@gmail.com
Subject: Re: [PATCH] ext4: improve str2hashbuf by processing 4-byte chunks
Date: Thu, 20 Nov 2025 10:58:16 -0500 [thread overview]
Message-ID: <20251120155816.GB13687@macsyma-3.local> (raw)
In-Reply-To: <20251116193513.0f90712a@pumpkin>
On Sun, Nov 16, 2025 at 07:35:13PM +0000, David Laight wrote:
>
> The (int) casts are unnecessary (throughout), 'char' is always promoted to
> 'signed int' before any arithmetic.
nit: in this case the casts aren't necessary, but your comment is not
correct in general, so I just wanted to make sure it's corrected in
case someone later looks at the mail archive.
"char" is not always signed. It can be signed or unsigned; the C
specification allows either. In this particular case, scp is a
"signed char", not "char".
Secondly, it's not that a promotion happens before "any" arithmetic.
If we add two 8-bit values together, promotion doesn't happen. In
this case, we are adding a signed char to an int, so the promotion
will happen.
Cheers,
- Ted
next prev parent reply other threads:[~2025-11-20 15:58 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-16 13:01 Guan-Chun Wu
2025-11-16 19:35 ` David Laight
2025-11-17 14:20 ` Guan-Chun Wu
2025-11-20 15:58 ` Theodore Tso [this message]
2025-11-20 16:58 ` Kuan-Wei Chiu
2025-11-20 18:27 ` David Laight
2025-11-21 10:07 ` Geert Uytterhoeven
2025-11-21 10:55 ` Andreas Schwab
2025-11-21 11:59 ` David Laight
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