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

[Kevin Traynor]

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.

> Signed-off-by: Xueming Li <xuemingl at 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.

> +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:
>