Re: [dpdk-dev] [PATCH v1] sched: adds function to get 64 bits greatest common divisor

["Xueming(Steven) Li" <xuemingl@nvidia.com>]

On Wed, 2021-09-22 at 18:09 +0100, Kevin Traynor wrote:
> On 15/09/2021 11:26, Xueming Li wrote:
> > This patch adds new function that compute the greatest common
> > divisor of 64 bits, also changes the original 32 bits function to call
> > this new 64 bits version.
> > 
> 
> Can you say why it is needed? It's unused apart from being called for 
> the original 32 bit version.

mlx5 vdpa driver is expecting to use a 64 bit version.

> 
> > Signed-off-by: Xueming Li <xuemingl@nvidia.com>
> > ---
> > v1: add 64 bits version and make 32 bits api call it
> > 
> >   lib/sched/rte_sched_common.h | 19 ++++++++++++++++---
> >   1 file changed, 16 insertions(+), 3 deletions(-)
> > 
> > diff --git a/lib/sched/rte_sched_common.h b/lib/sched/rte_sched_common.h
> > index 96706df7bd..1056543a84 100644
> > --- a/lib/sched/rte_sched_common.h
> > +++ b/lib/sched/rte_sched_common.h
> > @@ -51,10 +51,10 @@ rte_min_pos_4_u16(uint16_t *x)
> >    *    gcd(a, b) = gcd(b, a mod b)
> >    *
> >    */
> > -static inline uint32_t
> > -rte_get_gcd(uint32_t a, uint32_t b)
> > +static inline uint64_t
> > +rte_get_gcd64(uint64_t a, uint64_t b)
> >   {
> > -	uint32_t c;
> > +	uint64_t c;
> >   
> >   	if (a == 0)
> >   		return b;
> > @@ -76,6 +76,19 @@ rte_get_gcd(uint32_t a, uint32_t b)
> >   	return a;
> >   }
> >   
> > +/*
> > + * Compute the Greatest Common Divisor (GCD) of two u32 numbers.
> > + * This implementation uses Euclid's algorithm:
> > + *    gcd(a, 0) = a
> > + *    gcd(a, b) = gcd(b, a mod b)
> > + *
> > + */
> 
> I would probably not describe the algorithm here as it is not 
> implemented in this function.

Thanks, I'll just mention that a 32 bit version of GCD.

> 
> > +static inline uint32_t
> > +rte_get_gcd(uint32_t a, uint32_t b)
> > +{
> > +	return rte_get_gcd64(a, b);
> > +}
> > +
> >   /*
> >    * Compute the Lowest Common Denominator (LCD) of two numbers.
> >    * This implementation computes GCD first:
> > 
>