Re: [dpdk-dev] [PATCH v2 1/2] eal: add API to align integer to previous power of 2

[Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>]

Hi Matan,

On Mon, Feb 19, 2018 at 12:09:46PM +0000, Matan Azrad wrote:
>
> Hi Pavan
> > From: Pavan Nikhilesh, Monday, February 19, 2018 1:37 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>
> > ---
> >  v2 Changes:
> >  - Modified api name to `rte_align(32/64)prevpow2` from
> > `rte_align(32/64)lowpow2`.
> >  - corrected fuction to return if the integer is already aligned to  power of 2.
> >
> >  lib/librte_eal/common/include/rte_common.h | 43
> > ++++++++++++++++++++++++++++++
> >  1 file changed, 43 insertions(+)
> >
> > diff --git a/lib/librte_eal/common/include/rte_common.h
> > b/lib/librte_eal/common/include/rte_common.h
> > index c7803e41c..b2017ee5c 100644
> > --- a/lib/librte_eal/common/include/rte_common.h
> > +++ b/lib/librte_eal/common/include/rte_common.h
> > @@ -259,6 +259,27 @@ 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
> > + */
> > +static inline uint32_t
> > +rte_align32prevpow2(uint32_t x)
> > +{
> > +	x |= x >> 1;
> > +	x |= x >> 2;
> > +	x |= x >> 4;
> > +	x |= x >> 8;
> > +	x |= x >> 16;
> > +
> > +	return x - (x >> 1);
> > +}
>
> Nice.
>
> Since you are using the same 5 lines from the rte_align32pow2() function, I think this part can be in a separate function to do reuse.
> Also the "fill ones 32" function can be used for other purpose.
> What do you think?

I do agree that it would be cleaner to have a common function for both, but not
able to decide on a appropriate function name "fill ones 32" doesn't convey
what the function truly does. If you have a cleaner name do suggest, i will
roll up a v3 adding the function and experimental tag.

Thanks,
Pavan

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