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

[Matan Azrad]

From: Pavan Nikhilesh, Wednesday, April 4, 2018 7:42 PM
> 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).

You probably mean rte_compat.h.

It is ok to add it, what is the issue with that?

> Besides it's a simple proven math API I don't think it will change anytime
> soon.

It has already discussed:
https://dpdk.org/dev/patchwork/patch/35211/

I think you need to add it anyway.

> Thanks,
> Pavan
> 
> >
> > Besides that,
> > Acked-by: Matan Azrad <matan at 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 at 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
> >