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Date: Mon, 15 May 2006 15:42:10 -0500
From: jschopp <jschopp@austin.ibm.com>
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To: Jon Mason <jdmason@us.ibm.com>
Subject: Re: [PATCH] remove powerpc bitops infavor of existing generic bitops
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> Ah but here's the trick, there is the same explicit call to ppc
> assembly.  The only function in the file removed is this one you pointed
> out, and the only caller of this function is ext2_ffz.  And the only
> user of ext2_ffz is find_next_zero_le_bit.  
> 
> Now the generic code is very similar to the file removed (`diff -Narup
> arch/powerpc/lib/bitops.c lib/find_next_bit.c` to see for yourself).  In
> the same place where ext2_ffz is called, ffz is called in the generic
> code.  Now if we look at the definition of ffz in
> include/asm-powerpc/bitops.h, we see it calls __ilog2 of that same file.
> __ilog2 is defined as: 
> 
> static __inline__ int __ilog2(unsigned long x)
> {
>         int lz;
> 
>         asm (PPC_CNTLZL "%0,%1" : "=r" (lz) : "r" (x));
>         return BITS_PER_LONG - 1 - lz;
> }
> 
> So, its really the same code :)

Good explination.  I'm convinced, so for what it's worth:

Acked-by: Joel Schopp <jschopp@austin.ibm.com>