From: "David Laight" <David.Laight@ACULAB.COM>
To: "David Laight" <David.Laight@ACULAB.COM>,
"Maciej Zenczykowski" <zenczykowski@gmail.com>,
"Maciej Zenczykowski" <maze@google.com>
Cc: <netdev@vger.kernel.org>
Subject: RE: [PATCH] net: pfifo_fast - use ffs(x)-1 instead of array lookup
Date: Tue, 13 Mar 2012 16:55:14 -0000 [thread overview]
Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B6EA1@saturn3.aculab.com> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B6E9E@saturn3.aculab.com>
> > + /* For i in 0..7 returns {-1, 0, 1, 0, 2, 0, 1, 0}[i] */
> > + return ((26468 >> (i+i)) & 3) - 1;
>
> That expression doesn't seem quite right to me ...
> return (int)(0x12131210 >> (i * 4)) & 3) - 1;
> probably does what is wanted.
Hmmm... I'm going blind - I read that as 'i+1' not 'i+i'.
But using 'i * 4' and putting the constant in base 16
make the code rather less obscure.
David
next prev parent reply other threads:[~2012-03-13 16:56 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-13 5:12 [PATCH] net: pfifo_fast - use ffs(x)-1 instead of array lookup Maciej Żenczykowski
2012-03-13 5:13 ` Maciej Żenczykowski
2012-03-13 5:54 ` David Miller
2012-03-13 7:21 ` Maciej Żenczykowski
2012-03-13 7:23 ` Maciej Żenczykowski
2012-03-13 7:25 ` David Miller
2012-03-13 7:25 ` David Miller
2012-03-13 11:04 ` David Laight
2012-03-13 16:55 ` David Laight [this message]
2012-03-13 17:34 ` Eric Dumazet
2012-03-13 20:37 ` Maciej Żenczykowski
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