Re: [PATCH 2/5] bitops: compile time optimization for hweight_long(CONSTANT)

[H. Peter Anvin]

On 02/14/2010 12:28 PM, Borislav Petkov wrote:
> 
> Hmm, basically, what PeterZ suggested is that I drop one indirection
> under __arch_hweightN, which would make x86-specific fallback functions
> superfluous.
> 
> IOW, what we have so far is:
> 
> #define hweightN(w) (__builtin_constant_p(w) ? __const_hweightN(w) : __arch_hweightN(w))
> 
> and have <asm-generic/bitops/arch_hweight.h> provide __arch_hweightN()
> -> __sw_hweightN wrappers per default, where the __sw_hweightN are the
> lib/hweight.c generic versions.
> 
> On architectures/CPUs which provide popcnt in
> hardware, we create __arch_hweightN implementations in
> <arch/[:ARCH_NAME:]/include/asm/bitops.h> overriding the
> <asm-generic/bitops/arch_hweight.h> versions by simply not including
> that last header.
> 
> Is that agreeable?
> 

That makes sense... after all, that's a pretty typical use of asm-generic.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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