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

[Matan Azrad]

Hi Pavan

Shouldn't the new APIs be tagged with the experimental tag as agreed?

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