Re: [PATCH 02/17] bitops: Add generic parity calculation for u64

[Yury Norov]

On Mon, Feb 24, 2025 at 12:42:02AM +0800, Kuan-Wei Chiu wrote:
> Several parts of the kernel open-code parity calculations using
> different methods. Add a generic parity64() helper implemented with the
> same efficient approach as parity8().

No reason to add parity32() and parity64() in separate patches
 
> Co-developed-by: Yu-Chun Lin <eleanor15x@xxxxxxxxx>
> Signed-off-by: Yu-Chun Lin <eleanor15x@xxxxxxxxx>
> Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
> ---
>  include/linux/bitops.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index fb13dedad7aa..67677057f5e2 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -281,6 +281,28 @@ static inline int parity32(u32 val)
>  	return (0x6996 >> (val & 0xf)) & 1;
>  }
>  
> +/**
> + * parity64 - get the parity of an u64 value
> + * @value: the value to be examined
> + *
> + * Determine the parity of the u64 argument.
> + *
> + * Returns:
> + * 0 for even parity, 1 for odd parity
> + */
> +static inline int parity64(u64 val)
> +{
> +	/*
> +	 * One explanation of this algorithm:
> +	 * https://funloop.org/codex/problem/parity/README.html

This is already referenced in sources. No need to spread it for more.

> +	 */
> +	val ^= val >> 32;
> +	val ^= val >> 16;
> +	val ^= val >> 8;
> +	val ^= val >> 4;
> +	return (0x6996 >> (val & 0xf)) & 1;

It's better to avoid duplicating the same logic again and again.

> +}
> +

So maybe make it a macro?