[Sheepdog] expected bit size of __ffs

[MORITA Kazutaka]

At Mon, 17 May 2010 17:03:56 -0700,
Steven Dake wrote:
> 
> On Tue, 2010-05-18 at 08:45 +0900, FUJITA Tomonori wrote:
> > On Mon, 17 May 2010 09:34:37 -0700
> > Steven Dake <sdake at redhat.com> wrote:
> > 
> > > Is __ffs expecting 64 bit parameters?  At line 18 of bitops.h, there is
> > > a >> by 32, which with a 32 bit parameter results in the value 0.
> 
> > I think that 'if (BITS_PER_LONG == 64)' trick works on 32-bit archs.
> >  
> 
> That patch looks good.
> 
> Regards
> -steve
> 

Applied, thanks.

Kazutaka

> > #define BITS_PER_LONG (BITS_PER_BYTE * sizeof(long))
> > 
> > static inline unsigned long __ffs(unsigned long word)
> > {
> > 	int num = 0;
> > 
> > 	if (BITS_PER_LONG == 64) {
> > 		if ((word & 0xffffffff) == 0) {
> > 			num += 32;
> > 			word >>= 32;
> > 		}
> > 	}
> > 
> > So we don't hit "word >>= 32" on 32-bit archs. We get a warning like
> > "right shift count >= width of type" on this though.
> > 
> > The following patch kills the warning with gcc's built-in ffs().
> > 
> > =
> > From: FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp>
> > Subject: [PATCH] use gcc built-in ffs()
> > 
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp>
> > ---
> >  include/bitops.h |   34 +---------------------------------
> >  1 files changed, 1 insertions(+), 33 deletions(-)
> > 
> > diff --git a/include/bitops.h b/include/bitops.h
> > index 6c85d5e..0e0f402 100644
> > --- a/include/bitops.h
> > +++ b/include/bitops.h
> > @@ -3,43 +3,11 @@
> >  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
> >  #define DECLARE_BITMAP(name,bits) \
> >  	unsigned long name[BITS_TO_LONGS(bits)]
> > -
> >  #define BITS_PER_LONG (BITS_PER_BYTE * sizeof(long))
> >  
> > +#define __ffs(x)  (x ? __builtin_ffsl(x) - 1 : 0)
> >  #define ffz(x)  __ffs(~(x))
> >  
> > -static inline unsigned long __ffs(unsigned long word)
> > -{
> > -	int num = 0;
> > -
> > -	if (BITS_PER_LONG == 64) {
> > -		if ((word & 0xffffffff) == 0) {
> > -			num += 32;
> > -			word >>= 32;
> > -		}
> > -	}
> > -
> > -	if ((word & 0xffff) == 0) {
> > -		num += 16;
> > -		word >>= 16;
> > -	}
> > -	if ((word & 0xff) == 0) {
> > -		num += 8;
> > -		word >>= 8;
> > -	}
> > -	if ((word & 0xf) == 0) {
> > -		num += 4;
> > -		word >>= 4;
> > -	}
> > -	if ((word & 0x3) == 0) {
> > -		num += 2;
> > -		word >>= 2;
> > -	}
> > -	if ((word & 0x1) == 0)
> > -		num += 1;
> > -	return num;
> > -}
> > -
> >  #define BITOP_WORD(nr)		((nr) / BITS_PER_LONG)
> >  
> >  static inline unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
> 
> -- 
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