Re: [RFC PATCH v1 2/6] lib: Implement find_{first,next,nth}_nor_bit, find_first_andnot_bit

[Yury Norov <yury.norov@gmail.com>]

On Fri, Aug 23, 2024 at 02:59:42PM -0400, Mathieu Desnoyers wrote:
> Allow finding the first, next, or nth bit within two input bitmasks
> which is zero in both masks.
> 
> Allow fiding the first bit within two input bitmasks which is set in
> first mask and cleared in the second mask. find_next_andnot_bit and
> find_nth_andnot_bit already exist, so find the first bit appears to be
> missing.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>

Acked-by: Yury Norov <yury.norov@gmail.com>

If it comes to v2, can you also add some sanity tests for the new API?

> ---
> Changes since v0:
> - Rename "notandnot" to "nor", document equivalence.
> - Move comment cleanups to a separate patch.
> - Use __always_inline.
> ---
>  include/linux/find.h | 112 +++++++++++++++++++++++++++++++++++++++++++
>  lib/find_bit.c       |  36 ++++++++++++++
>  2 files changed, 148 insertions(+)
> 
> diff --git a/include/linux/find.h b/include/linux/find.h
> index 8a170aa55634..b1394ba92654 100644
> --- a/include/linux/find.h
> +++ b/include/linux/find.h
> @@ -14,6 +14,8 @@ unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long
>  					unsigned long nbits, unsigned long start);
>  unsigned long _find_next_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
>  					unsigned long nbits, unsigned long start);
> +unsigned long _find_next_nor_bit(const unsigned long *addr1, const unsigned long *addr2,
> +					unsigned long nbits, unsigned long start);
>  unsigned long _find_next_or_bit(const unsigned long *addr1, const unsigned long *addr2,
>  					unsigned long nbits, unsigned long start);
>  unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
> @@ -24,11 +26,17 @@ unsigned long __find_nth_and_bit(const unsigned long *addr1, const unsigned long
>  				unsigned long size, unsigned long n);
>  unsigned long __find_nth_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
>  					unsigned long size, unsigned long n);
> +unsigned long __find_nth_nor_bit(const unsigned long *addr1, const unsigned long *addr2,
> +					unsigned long size, unsigned long n);
>  unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
>  					const unsigned long *addr3, unsigned long size,
>  					unsigned long n);
>  extern unsigned long _find_first_and_bit(const unsigned long *addr1,
>  					 const unsigned long *addr2, unsigned long size);
> +extern unsigned long _find_first_andnot_bit(const unsigned long *addr1,
> +					 const unsigned long *addr2, unsigned long size);
> +extern unsigned long _find_first_nor_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);
> @@ -130,6 +138,35 @@ unsigned long find_next_andnot_bit(const unsigned long *addr1,
>  }
>  #endif
>  
> +/**
> + * find_next_nor_bit - find the next bit cleared in both *addr1 and *addr2
> + * @addr1: The first address to base the search on
> + * @addr2: The second address to base the search on
> + * @size: The bitmap size in bits
> + * @offset: The bitnumber to start searching at
> + *
> + * Returns the bit number for the next bit cleared in both *addr1 and *addr2.
> + * If no such bits are found, returns @size.
> + * The bitwise operation nor ~(A | B) is equivalent to (~A & ~B).
> + */
> +static __always_inline
> +unsigned long find_next_nor_bit(const unsigned long *addr1,
> +		const unsigned long *addr2, unsigned long size,
> +		unsigned long offset)
> +{
> +	if (small_const_nbits(size)) {
> +		unsigned long val;
> +
> +		if (unlikely(offset >= size))
> +			return size;
> +
> +		val = ~(*addr1 | *addr2) & GENMASK(size - 1, offset);
> +		return val ? __ffs(val) : size;
> +	}
> +
> +	return _find_next_nor_bit(addr1, addr2, size, offset);
> +}
> +
>  #ifndef find_next_or_bit
>  /**
>   * find_next_or_bit - find the next set bit in either memory regions
> @@ -291,6 +328,33 @@ unsigned long find_nth_andnot_bit(const unsigned long *addr1, const unsigned lon
>  	return __find_nth_andnot_bit(addr1, addr2, size, n);
>  }
>  
> +/**
> + * find_nth_nor_bit - find N'th cleared bit in 2 memory regions.
> + * @addr1: The 1st address to start the search at
> + * @addr2: The 2nd address to start the search at
> + * @size: The maximum number of bits to search
> + * @n: The number of set bit, which position is needed, counting from 0
> + *
> + * Returns the bit number of the N'th bit cleared in the two regions.
> + * If no such, returns @size.
> + * The bitwise operation nor ~(A | B) is equivalent to (~A & ~B).
> + */
> +static __always_inline
> +unsigned long find_nth_nor_bit(const unsigned long *addr1, const unsigned long *addr2,
> +				unsigned long size, unsigned long n)
> +{
> +	if (n >= size)
> +		return size;
> +
> +	if (small_const_nbits(size)) {
> +		unsigned long val = ~(*addr1 | *addr2) & GENMASK(size - 1, 0);
> +
> +		return val ? fns(val, n) : size;
> +	}
> +
> +	return __find_nth_nor_bit(addr1, addr2, size, n);
> +}
> +
>  /**
>   * find_nth_and_andnot_bit - find N'th set bit in 2 memory regions,
>   *			     excluding those set in 3rd region
> @@ -346,6 +410,54 @@ unsigned long find_first_and_bit(const unsigned long *addr1,
>  }
>  #endif
>  
> +/**
> + * find_first_andnot_bit - find the first set bit in 2 memory regions,
> + *                         flipping bits in 2nd region.
> + * @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 next 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)
> +{
> +	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_nor_bit - find the first cleared bit in 2 memory regions
> + * @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 next cleared bit.
> + * If no bits are set, returns @size.
> + * The bitwise operation nor ~(A | B) is equivalent to (~A & ~B).
> + */
> +static __always_inline
> +unsigned long find_first_nor_bit(const unsigned long *addr1,
> +				 const unsigned long *addr2,
> +				 unsigned long size)
> +{
> +	if (small_const_nbits(size)) {
> +		unsigned long val = ~(*addr1 | *addr2) & GENMASK(size - 1, 0);
> +
> +		return val ? __ffs(val) : size;
> +	}
> +
> +	return _find_first_nor_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..8050bc7c7ede 100644
> --- a/lib/find_bit.c
> +++ b/lib/find_bit.c
> @@ -116,6 +116,28 @@ unsigned long _find_first_and_bit(const unsigned long *addr1,
>  EXPORT_SYMBOL(_find_first_and_bit);
>  #endif
>  
> +/*
> + * Find the first set bit in two memory regions, flipping bits in 2nd region.
> + */
> +unsigned long _find_first_andnot_bit(const unsigned long *addr1,
> +				  const unsigned long *addr2,
> +				  unsigned long size)
> +{
> +	return FIND_FIRST_BIT(addr1[idx] & ~addr2[idx], /* nop */, size);
> +}
> +EXPORT_SYMBOL(_find_first_andnot_bit);
> +
> +/*
> + * Find the first cleared bit in two memory regions.
> + */
> +unsigned long _find_first_nor_bit(const unsigned long *addr1,
> +				  const unsigned long *addr2,
> +				  unsigned long size)
> +{
> +	return FIND_FIRST_BIT(~(addr1[idx] | addr2[idx]), /* nop */, size);
> +}
> +EXPORT_SYMBOL(_find_first_nor_bit);
> +
>  /*
>   * Find the first set bit in three memory regions.
>   */
> @@ -167,6 +189,13 @@ unsigned long __find_nth_andnot_bit(const unsigned long *addr1, const unsigned l
>  }
>  EXPORT_SYMBOL(__find_nth_andnot_bit);
>  
> +unsigned long __find_nth_nor_bit(const unsigned long *addr1, const unsigned long *addr2,
> +				 unsigned long size, unsigned long n)
> +{
> +	return FIND_NTH_BIT(~(addr1[idx] | addr2[idx]), size, n);
> +}
> +EXPORT_SYMBOL(__find_nth_nor_bit);
> +
>  unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1,
>  					const unsigned long *addr2,
>  					const unsigned long *addr3,
> @@ -194,6 +223,13 @@ unsigned long _find_next_andnot_bit(const unsigned long *addr1, const unsigned l
>  EXPORT_SYMBOL(_find_next_andnot_bit);
>  #endif
>  
> +unsigned long _find_next_nor_bit(const unsigned long *addr1, const unsigned long *addr2,
> +					unsigned long nbits, unsigned long start)
> +{
> +	return FIND_NEXT_BIT(~(addr1[idx] | addr2[idx]), /* nop */, nbits, start);
> +}
> +EXPORT_SYMBOL(_find_next_nor_bit);
> +
>  #ifndef find_next_or_bit
>  unsigned long _find_next_or_bit(const unsigned long *addr1, const unsigned long *addr2,
>  					unsigned long nbits, unsigned long start)
> -- 
> 2.39.2