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Date: Sat, 19 Dec 2009 15:34:29 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: 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
Message-ID: <20091219143425.GA5003@nowhere>
References: <1261173920-11320-1-git-send-regression-fweisbec@gmail.com> <1261214767.20899.697.camel@laptop>
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On Sat, Dec 19, 2009 at 10:26:07AM +0100, Peter Zijlstra wrote:
> On Fri, 2009-12-18 at 23:05 +0100, Frederic Weisbecker wrote:
> > +#ifndef BITS_PER_LONG
> >  /* CHECKME: Not sure both always match */
> >  #define BITS_PER_LONG  __WORDSIZE
> > +#endif 
> 
> Why use __WORDSIZE if you're not sure?
> 
> (8*sizeof(long)) is simple and unambiguous.


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 :)