Re: [dpdk-dev] [PATCH v3 1/2] eal: add API to align integer to previous power of 2

[Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>]

Hi Matan,

On Wed, Apr 04, 2018 at 04:10:36PM +0000, Matan Azrad wrote:
> Hi Pavan
>
> Shouldn't the new APIs be tagged with the experimental tag as agreed?

Can't tag it experimental as it causes cyclic dependency (need to include
rte_compact.h).
Besides it's a simple proven math API I don't think it will change anytime
soon.

Thanks,
Pavan

>
> Besides that,
> Acked-by: Matan Azrad <matan@mellanox.com>
>
> From: Pavan Nikhilesh, Wednesday, April 4, 2018 1:16 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>
> > ---
> >  v3 Changes:
> >  - Move commonly used code to rte_combine(32/64)ms1b so that it can be
> > reused.
> >
> >  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 | 92
> > ++++++++++++++++++++++++++----
> >  1 file changed, 81 insertions(+), 11 deletions(-)
> >
> > diff --git a/lib/librte_eal/common/include/rte_common.h
> > b/lib/librte_eal/common/include/rte_common.h
> > index c7803e41c..7e147dcf2 100644
> > --- a/lib/librte_eal/common/include/rte_common.h
> > +++ b/lib/librte_eal/common/include/rte_common.h
> > @@ -223,6 +223,51 @@ extern int RTE_BUILD_BUG_ON_detected_error;  }
> > while(0)  #endif
> >
> > +/**
> > + * Combines 32b inputs most significant set bits into the least
> > + * significant bits to construct a value with the same MSBs as x
> > + * but all 1's under it.
> > + *
> > + * @param x
> > + *    The integer whose MSBs need to be combined with its LSBs
> > + * @return
> > + *    The combined value.
> > + */
> > +static inline uint32_t
> > +rte_combine32ms1b(register uint32_t x)
> > +{
> > +	x |= x >> 1;
> > +	x |= x >> 2;
> > +	x |= x >> 4;
> > +	x |= x >> 8;
> > +	x |= x >> 16;
> > +
> > +	return x;
> > +}
> > +
> > +/**
> > + * Combines 64b inputs most significant set bits into the least
> > + * significant bits to construct a value with the same MSBs as x
> > + * but all 1's under it.
> > + *
> > + * @param v
> > + *    The integer whose MSBs need to be combined with its LSBs
> > + * @return
> > + *    The combined value.
> > + */
> > +static inline uint64_t
> > +rte_combine64ms1b(register uint64_t v)
> > +{
> > +	v |= v >> 1;
> > +	v |= v >> 2;
> > +	v |= v >> 4;
> > +	v |= v >> 8;
> > +	v |= v >> 16;
> > +	v |= v >> 32;
> > +
> > +	return v;
> > +}
> > +
> >  /*********** Macros to work with powers of 2 ********/
> >
> >  /**
> > @@ -250,15 +295,28 @@ static inline uint32_t  rte_align32pow2(uint32_t x)  {
> >  	x--;
> > -	x |= x >> 1;
> > -	x |= x >> 2;
> > -	x |= x >> 4;
> > -	x |= x >> 8;
> > -	x |= x >> 16;
> > +	x = rte_combine32ms1b(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 = rte_combine32ms1b(x);
> > +
> > +	return x - (x >> 1);
> > +}
> > +
> >  /**
> >   * Aligns 64b input parameter to the next power of 2
> >   *
> > @@ -272,16 +330,28 @@ static inline uint64_t  rte_align64pow2(uint64_t v)  {
> >  	v--;
> > -	v |= v >> 1;
> > -	v |= v >> 2;
> > -	v |= v >> 4;
> > -	v |= v >> 8;
> > -	v |= v >> 16;
> > -	v |= v >> 32;
> > +	v = rte_combine64ms1b(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_align64prevpow2(uint64_t v)
> > +{
> > +	v = rte_combine64ms1b(v);
> > +
> > +	return v - (v >> 1);
> > +}
> > +
> >  /*********** Macros for calculating min and max **********/
> >
> >  /**
> > --
> > 2.16.3
>