Re: [PATCH v11 02/30] find: add find_first_andnot_bit()

[Fenghua Yu <fenghuay@nvidia.com>]

Hi, James and Yury,

On 5/13/25 10:15, James Morse wrote:
> From: "Yury Norov [NVIDIA]" <yury.norov@gmail.com>
>
> The function helps to implement cpumask_andnot() APIs.
>
> Tested-by: James Morse <james.morse@arm.com>
> Reviewed-by: James Morse <james.morse@arm.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>   include/linux/find.h | 25 +++++++++++++++++++++++++
>   lib/find_bit.c       | 11 +++++++++++
>   2 files changed, 36 insertions(+)
>
> diff --git a/include/linux/find.h b/include/linux/find.h
> index 68685714bc18..5a2c267ea7f9 100644
> --- a/include/linux/find.h
> +++ b/include/linux/find.h
> @@ -29,6 +29,8 @@ unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1, const unsign
>   					unsigned long n);
>   extern unsigned long _find_first_and_bit(const unsigned long *addr1,
>   					 const unsigned long *addr2, unsigned long size);
> +unsigned long _find_first_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
> +				 unsigned long size);
>   unsigned long _find_first_and_and_bit(const unsigned long *addr1, const unsigned long *addr2,
>   				      const unsigned long *addr3, unsigned long size);
>   extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
> @@ -347,6 +349,29 @@ unsigned long find_first_and_bit(const unsigned long *addr1,
>   }
>   #endif
>   
> +/**
> + * find_first_andnot_bit - find the first bit set in 1st memory region and unset in 2nd
> + * @addr1: The first address to base the search on
> + * @addr2: The second address to base the search on
> + * @size: The bitmap size in bits
> + *
> + * Returns the bit number for the first set bit
> + * If no bits are set, returns >= @size.
> + */
> +static __always_inline
> +unsigned long find_first_andnot_bit(const unsigned long *addr1,
> +				 const unsigned long *addr2,
> +				 unsigned long size)
CHECK: Alignment should match open parenthesis

> +{
> +	if (small_const_nbits(size)) {
> +		unsigned long val = *addr1 & (~*addr2) & GENMASK(size - 1, 0);
> +
> +		return val ? __ffs(val) : size;
> +	}
> +
> +	return _find_first_andnot_bit(addr1, addr2, size);
> +}
> +
>   /**
>    * find_first_and_and_bit - find the first set bit in 3 memory regions
>    * @addr1: The first address to base the search on
> diff --git a/lib/find_bit.c b/lib/find_bit.c
> index 0836bb3d76c5..06b6342aa3ae 100644
> --- a/lib/find_bit.c
> +++ b/lib/find_bit.c
> @@ -116,6 +116,17 @@ unsigned long _find_first_and_bit(const unsigned long *addr1,
>   EXPORT_SYMBOL(_find_first_and_bit);
>   #endif
>   
> +/*
> + * Find the first bit set in 1st memory region and unset in 2nd.
> + */
> +unsigned long _find_first_andnot_bit(const unsigned long *addr1,
> +				  const unsigned long *addr2,
> +				  unsigned long size)
Ditto.
> +{
> +	return FIND_FIRST_BIT(addr1[idx] & ~addr2[idx], /* nop */, size);
> +}
> +EXPORT_SYMBOL(_find_first_andnot_bit);
> +
>   /*
>    * Find the first set bit in three memory regions.
>    */

Thanks.

-Fenghua