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From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH] perf tools: Prevent from BITS_PER_LONG redefinition
Date: Thu, 31 Dec 2009 22:09:43 +1100	[thread overview]
Message-ID: <4B3C8677.3030606@goop.org> (raw)
In-Reply-To: <20091230214549.GF6322@nowhere>

On 12/31/2009 08:45 AM, Frederic Weisbecker wrote:
>> You can use if() with a constant expression instead of #if.
>>      
>
>
> I did not write this code. But yes you're right, although I
> think CPP is more suitable here because fls() can be called
> from fastpath and this conditional build makes one check less
> and lesser i-cache footprint.
>    

Constant if()s are removed at compile time, so there should be no 
runtime overhead.  Constant if()s are generally preferable to #if 
because the compile will statically check the other code branch, even if 
it never gets executed, which helps prevent it from rotting.

     J


  reply	other threads:[~2010-01-02  5:47 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-12-18 22:05 [PATCH] perf tools: Prevent from BITS_PER_LONG redefinition Frederic Weisbecker
2009-12-19  9:26 ` Peter Zijlstra
2009-12-19 14:34   ` Frederic Weisbecker
2009-12-20  5:11     ` Jeremy Fitzhardinge
2009-12-30 21:45       ` Frederic Weisbecker
2009-12-31 11:09         ` Jeremy Fitzhardinge [this message]
2010-01-02 17:01           ` Frederic Weisbecker

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