Re: [PATCH 1/2] eal: add API to align integer to previous power of 2

[Matan Azrad <matan@mellanox.com>]

> From: Wiles, Keith, Sunday, February 18, 2018 5:39 PM
> > On Feb 18, 2018, at 12:11 AM, Matan Azrad <matan@mellanox.com>
> wrote:
> >
> > Hi Pavan
> >
> > Please see some comments below.
> >
> > From: Pavan Nikhilesh, Saturday, February 17, 2018 12:50 PM
> >> Add 32b and 64b API's to align the given integer to the previous power of
> 2.
> >>
> >> Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> >> ---
> >> lib/librte_eal/common/include/rte_common.h | 36
> >> ++++++++++++++++++++++++++++++
> >> 1 file changed, 36 insertions(+)
> >>
> >> diff --git a/lib/librte_eal/common/include/rte_common.h
> >> b/lib/librte_eal/common/include/rte_common.h
> >> index c7803e41c..126914f07 100644
> >> --- a/lib/librte_eal/common/include/rte_common.h
> >> +++ b/lib/librte_eal/common/include/rte_common.h
> >> @@ -259,6 +259,24 @@ rte_align32pow2(uint32_t x)
> >> 	return x + 1;
> >> }
> >>
> >> +/**
> >> + * Aligns input parameter to the previous power of 2
> >> + *
> >> + * @param x
> >> + *   The integer value to algin
> >> + *
> >> + * @return
> >> + *   Input parameter aligned to the previous power of 2
> >
> > I think the zero case(x=0) result should be documented.
> >
> >> + */
> >> +static inline uint32_t
> >> +rte_align32lowpow2(uint32_t x)
> >
> > What do you think about " rte_align32prevpow2"?
> >
> >> +{
> >> +	x = rte_align32pow2(x);
> >
> > 	In case of  x is power of 2 number(already aligned), looks like the
> result here is x and the final result is (x >> 1)?
> > 	Is it as you expect?
> >
> >> +	x--;
> >> +
> >> +	return x - (x >> 1);
> >
> > Why can't the implementation just be:
> > return  rte_align32pow2(x) >> 1;
> >
> > If the above is correct, Are you sure we need this API?
> >
> >> +}
> >> +
> >> /**
> >>  * Aligns 64b input parameter to the next power of 2
> >>  *
> >> @@ -282,6 +300,24 @@ rte_align64pow2(uint64_t v)
> >> 	return v + 1;
> >> }
> >>
> >> +/**
> >> + * Aligns 64b input parameter to the previous power of 2
> >> + *
> >> + * @param v
> >> + *   The 64b value to align
> >> + *
> >> + * @return
> >> + *   Input parameter aligned to the previous power of 2
> >> + */
> >> +static inline uint64_t
> >> +rte_align64lowpow2(uint64_t v)
> >> +{
> >> +	v = rte_align64pow2(v);
> >> +	v--;
> >> +
> >> +	return v - (v >> 1);
> >> +}
> >> +
> >
> > Same comments for 64b API.
> >
> >> /*********** Macros for calculating min and max **********/
> >>
> >> /**
> >> --
> >> 2.16.1
> >
> >
> > If it is a new API, I think it should be added to the map file and to be tagged
> as experimental. No?
> >
> 
> Is this the type of API that needs to be marked experimental,

I think it is relevant to any exposed API(not only for internal libraries).

> we should be able to prove these functions, correct?

Don't we need to prove any function in DPDK?
What is your point?

> > Matan
> 
> Regards,
> Keith