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

[Matan Azrad <matan@mellanox.com>]

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?
 

>  /**
>   * Aligns 64b input parameter to the next power of 2
>   *
> @@ -282,6 +303,28 @@ rte_align64pow2(uint64_t 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 |= v >> 1;
> +	v |= v >> 2;
> +	v |= v >> 4;
> +	v |= v >> 8;
> +	v |= v >> 16;
> +	v |= v >> 32;
> +
> +	return v - (v >> 1);
> +}
> +
>  /*********** Macros for calculating min and max **********/
> 
>  /**
> --
> 2.16.1