linux-kernel - Re: [PATCH] perf tools: Prevent from BITS_PER

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Date:	Sat, 19 Dec 2009 21:11:20 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] perf tools: Prevent from BITS_PER_LONG redefinition

On 12/19/2009 06:34 AM, Frederic Weisbecker wrote:
> Yeah but we need it from the CPP level.
> We include such code located in kernel headers:
>
> static __always_inline unsigned long __fls(unsigned long word)
> {
> 	int num = BITS_PER_LONG - 1;
>
> #if BITS_PER_LONG == 64
> 	if (!(word&  (~0ul<<  32))) {
> 		num -= 32;
> 		word<<= 32;
> 	}
> #endif
> 	if (!(word&  (~0ul<<  (BITS_PER_LONG-16)))) {
> 		num -= 16;
> 		word<<= 16;
> 	}
>
>
> And sizeof() is not defined :)
>    

You can use if() with a constant expression instead of #if.

     J
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