Re: [PATCH] x86: merge the simple bitops and move them to bitops.h

[Jeremy Fitzhardinge]

Alexander van Heukelum wrote:
> On Fri, 14 Mar 2008 11:07:55 -0700, "Jeremy Fitzhardinge"
> <jeremy@xxxxxxxx> said:
>   
> > Alexander van Heukelum wrote:
> >     
> > > x86: merge the simple bitops and move them to bitops.h
> > >
> > > Some of those can be written in such a way that the same
> > > inline assembly can be used to generate both 32 bit and
> > > 64 bit code.
> > >
> > > For ffs and fls, x86_64 unconditionally used the cmov
> > > instruction and i386 unconditionally used a conditional
> > > branch over a mov instruction. In the current patch I
> > > chose to select the version based on the availability
> > > of the cmov instruction instead. A small detail here is
> > > that x86_64 did not previously set CONFIG_X86_CMOV=y.
> > >   
> > >       
> > Looks good in general.  What's left in bitops_{32,64}.h now?
> >     
>
> Thanks for taking a look!
>
> bitops_{32,64}.h are getting pretty empty ;)
>
> Both contain find_first_bit/find_first_zero_bit, i386 has them inlined,
> x86_64 has an ugly define to select between small bitmaps (inlined) and
> an out-of-line version. I think they should be unified much like how
> find_next_bit and find_next_zero_bit work now (in x86#testing).
>
> Both define fls64(), but i386 uses a generic one and x86_64 defines
> one all by itself. The generic one is currently not suitable for
> use by 64-bit archs... that can change.
>
> x86_64 defines ARCH_HAS_FAST_MULTIPLIER, i386 not. This affects a
> choice of generated code in the (generic) hweight function. It would
> be nice if that could move to some other file.
>
> x86_64 has a mysterious inline function set_bit_string, which is
> only used by pci-calgary_64.c and pci-gart_64.c. Not sure what to
> do with it.
>
>   
> > (Some comments below.)
> >     
>
> --- %< ---
>
>   
> > > +#ifdef __KERNEL__
> > > +/**
> > > + * ffs - find first bit set
> > > + * @x: the word to search
> > > + *
> > > + * This is defined the same way as
> > > + * the libc and compiler builtin ffs routines, therefore
> > > + * differs in spirit from the above ffz() (man ffs).
> > >       
> > This comment seems wrong.  My "man ffs" says that it returns 1-32 for 
> > non-zero inputs, and 0 for a zero input.  This function returns 0-31, or 
> > -1 for a zero input.
> >     
>
> Seems, indeed. You missed the "return r + 1;" ;-)
>   

Indeed I did.

   J
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