Hi Antonio, Steffan,
On Thu, Jun 22, 2017 at 3:31 PM, Antonio Quartulli <a...@unstable.cc> wrote:
> Thanks for sending v2 Steffan,
>
> On Wed, Jun 21, 2017 at 11:10:43PM +0200, Steffan Karger wrote:
> > From: Steffan Karger <steffan.kar...@fox-it.com>
> >
> > misc.c is a mess of incoherent functions, and is therefore included by
> > virtually all our source files. That makes testing harder than it should
> > be. As a first step of cleaning up misc.c, move adjust_power_of_2() to
> > integer.h, which is a more suitable place for a function like this.
> >
> > This allows us to remove the duplicate implementation from test_argv.c.
> >
> > Signed-off-by: Steffan Karger <steffan.kar...@fox-it.com>
>
>
> This change is quite simple and passes basic tests.
> Thanks also for adding explicit #include statements.
>
> Acked-by: Antonio Quartulli <anto...@openvpn.net>
>
>
Since the code is moved, would it be interesting to use a less greedy
algorithm to do the same thing? I know the function is not used very often,
so it does not look like it's necessary (it's a suggestion, not a
commentary on your patch Steffan :))
For example, this code:
size_t
adjust_power_of_2(size_t v)
{
if (!v)
return 1;
v--;
v |= v >> 1;
v |= v >> 2;
v |= v >> 4;
v |= v >> 8;
v |= v >> 16;
if (sizeof(size_t) == 8)
v |= v >> 32;
v++;
return v;
}
does the exact same work on a 64 size_t but will be far faster than the
loop-based one on many situation (the sizeof() test should be optimized
away if it's never true, so the code will work even with a 32 bit size_t).
Why it works:
* if (v - 1) has 0 bits set, then v = 1 and the function will return 1 ((0
| 0 | ... | 0) + 1)
* if (v - 1) has at least one bit set (let's say it's bit n), then the
first iteration will set bit (n-1). The next iteration will set bits (n-2)
and (n-3). We goes on for a few steps. Before the last iteration, v has
bits (n...(n-32)) set (with sizeof(size_t) == 8), so the very last
operation fills the remaining bits and v has bits (n...0) set. Adding one
to this value will yield the desired result.
Again, the function is not used extensively, so you can ignore this
suggestion as it will not speed up openvpn at all :)
> Cheers,
>
>
BR,
-- Emmanuel Deloget
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