Date: Fri, 16 Jan 2004 00:35:20 -0800
From: Andrew Morton <akpm@osdl.org>
To: Andi Kleen <ak@muc.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: seperator error in __mask_snprintf_len
Message-Id: <20040116003520.3b55aa8e.akpm@osdl.org>
In-Reply-To: <m3n08o1erp.fsf@averell.firstfloor.org>
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	<m3n08o1erp.fsf@averell.firstfloor.org>
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Andi Kleen <ak@muc.de> wrote:
>
> Andrew Morton <akpm@osdl.org> writes:
> 
> > +void bitmap_complement(unsigned long *bitmap, int bits)
> > +{
> > +	int k;
> > +
> > +	for (k = 0; k < BITS_TO_LONGS(bits); ++k)
> > +		bitmap[k] = ~bitmap[k];
> > +}
> > +EXPORT_SYMBOL(bitmap_complement);
> 
> I actually had to change that one in my NUMA API patchkit (which uses
> bitmap functions for its node maps), because gcc 3.2 miscompiled the
> loop.
>
> Please add something like that (looks silly, but makes a big 
> difference):
> 
>  static inline void bitmap_complement(unsigned long *bitmap, int bits)
>  {
>         int k;
> +       int max = BITS_TO_LONGS(bits);
>  
> -       for (k = 0; k < BITS_TO_LONGS(bits); ++k)
> +       for (k = 0; k < max; ++k)
>                 bitmap[k] = ~bitmap[k];

OK.  bitmap_and() and bitmap_or() were converted to this form a while back
because they too were hitting the bug.  On ia32.  It might no longer
happen now they're uninlined but whatever - you don't have to look
at the code and think "gee, I hope the compiler moves that arith out
of the loop".


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