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From: H. Peter Anvin on 3 Feb 2010 12:20
On 02/03/2010 05:39 AM, Wu Fengguang wrote:
>
>> (I wonder if it could have used __builtin_popcount)
>>
>> (I wonder which gcc versions support __builtin_popcount)
>

I think 4.0 or later, but it often generates calls to libgcc, which
would mean adding libgcc functions to the kernel (which some arches
already do.)

> This is how Jamie Lokier first recommended it to me:
>
> Checked GCC 3.4.3 / 4.1 / 4.4: It expands as a compile-time
> constant if the argument is a compile-time constant, so can be
> used in BUILD_BUG_ON() and even for array sizes etc.
>
> Is there an official lowest GCC version that Linux supports?

3.4, I believe.

-hpa

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

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