From: Eric Dumazet <eric.dumazet@gmail.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Joe Perches <joe@perches.com>, David Miller <davem@davemloft.net>,
jeffrey.t.kirsher@intel.com, netdev@vger.kernel.org,
linux-wireless <linux-wireless@vger.kernel.org>
Subject: RE: [PATCH net-next] drivers/net: Remove boolean comparisons to true/false
Date: Fri, 10 Feb 2012 14:04:22 +0100 [thread overview]
Message-ID: <1328879062.2443.16.camel@edumazet-laptop> (raw)
In-Reply-To: <AE90C24D6B3A694183C094C60CF0A2F6026B6E65@saturn3.aculab.com>
Le vendredi 10 février 2012 à 09:32 +0000, David Laight a écrit :
> The generated code is particularly horrid for boolean arithmetic.
> IIRC:
> bool_var &= bool_var_1;
> typically requires a sequence of compare and branch instructions.
>
I suggest you try to upgrade your old compiler and/or always check your
assertions before posting on netdev such claims.
bool_var &= bool_var_1;
generates a single AND instruction, no compare, no branch.
It would be a failure from compiler optimizer if that was the case.
And (bool_var ? 1 : 0) or (!!bool_var) are NOP for a compiler as well.
(Only one movzbl instruction to convert a byte to a word if context
requires this)
Only difference for bool or unsigned int vars is type promotion, and
fact that compiler knows that 'bool' only can be 0 or 1, so allows more
optimisations than plain "unsigned int".
Really, bools are not evil if well used.
next prev parent reply other threads:[~2012-02-10 13:04 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1328783282-17760-5-git-send-email-jeffrey.t.kirsher@intel.com>
[not found] ` <AE90C24D6B3A694183C094C60CF0A2F6026B6E62@saturn3.aculab.com>
[not found] ` <20120209.133413.349832435589531136.davem@davemloft.net>
2012-02-09 21:17 ` [PATCH net-next] drivers/net: Remove boolean comparisons to true/false Joe Perches
2012-02-09 21:28 ` Jeff Kirsher
2012-02-09 22:36 ` Allan, Bruce W
2012-02-09 23:08 ` Joe Perches
2012-02-10 6:46 ` Julia Lawall
2012-02-10 9:32 ` David Laight
2012-02-10 9:50 ` Arend van Spriel
2012-02-10 13:04 ` Eric Dumazet [this message]
2012-02-13 5:50 ` David Miller
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