Re: [RFC 1/2] eal: add bitset type

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Tue, Feb 28, 2023 at 10:39:15AM +0100, Mattias Rönnblom wrote:
> Introduce a set of functions and macros that operate on sets of bits,
> kept in arrays of 64-bit elements.
> 
> RTE bitset is designed for bitsets which are larger than what fits in
> a single machine word (i.e., 64 bits). For very large bitsets, the
> <rte_bitmap.h> API may be a more appropriate choice.
> 
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> ---

...

> diff --git a/lib/eal/include/rte_bitset.h b/lib/eal/include/rte_bitset.h
> new file mode 100644
> index 0000000000..e333e527e5
> --- /dev/null
> +++ b/lib/eal/include/rte_bitset.h
> @@ -0,0 +1,878 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2023 Ericsson AB
> + */
> +
> +#ifndef _RTE_BITSET_H_
> +#define _RTE_BITSET_H_
> +
> +/**
> + * @file
> + * RTE Bitset
> + *
> + * This file provides functions and macros for querying and
> + * manipulating sets of bits kept in arrays of @c uint64_t-sized
> + * elements.
> + *
> + * The bits in a bitset are numbered from 0 to @c size - 1, with the
> + * lowest index being the least significant bit.
> + *
> + * The bitset array must be properly aligned.
> + *
> + * For optimal performance, the @c size parameter, required by
> + * many of the API's functions, should be a compile-time constant.
> + *
> + * For large bitsets, the rte_bitmap.h API may be more appropriate.
> + *
> + * @warning
> + * All functions modifying a bitset may overwrite any unused bits of
> + * the last word. Such unused bits are ignored by all functions reading
> + * bits.
> + *
> + */
> +
> +#include <limits.h>
> +#include <stdbool.h>
> +#include <stdint.h>
> +#include <sys/types.h>

windows has no sys/types.h if there is a shim being picked up somewhere
portable code shouldn't depend on sys/types.h

> +
> +#include <rte_branch_prediction.h>
> +#include <rte_common.h>
> +#include <rte_debug.h>
> +#include <rte_memcpy.h>
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +/**
> + * The size (in bytes) of each element in the array used to represent
> + * a bitset.
> + */
> +#define RTE_BITSET_WORD_SIZE (sizeof(uint64_t))
> +
> +/**
> + * The size (in bits) of each element in the array used to represent
> + * a bitset.
> + */
> +#define RTE_BITSET_WORD_BITS (RTE_BITSET_WORD_SIZE * CHAR_BIT)
> +
> +/**
> + * Computes the number of words required to store @c size bits.
> + */
> +#define RTE_BITSET_NUM_WORDS(size)			       \
> +	((size + RTE_BITSET_WORD_BITS - 1) / RTE_BITSET_WORD_BITS)
> +
> +/**
> + * Computes the amount of memory (in bytes) required to fit a bitset
> + * holding @c size bits.
> + */
> +#define RTE_BITSET_SIZE(size)					\
> +	((size_t)(RTE_BITSET_NUM_WORDS(size) * RTE_BITSET_WORD_SIZE))
> +
> +#define __RTE_BITSET_WORD_IDX(bit_num) ((bit_num) / RTE_BITSET_WORD_BITS)
> +#define __RTE_BITSET_BIT_OFFSET(bit_num) ((bit_num) % RTE_BITSET_WORD_BITS)
> +#define __RTE_BITSET_UNUSED(size)				\
> +	((RTE_BITSET_NUM_WORDS(size) * RTE_BITSET_WORD_BITS) \
> +	 - (size))
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Declare a bitset.
> + *
> + * Declare (e.g., as a struct field) or define (e.g., as a stack
> + * variable) a bitset of the specified size.
> + *
> + * @param size
> + *   The number of bits the bitset must be able to represent. Must be
> + *   a compile-time constant.
> + * @param name
> + *   The field or variable name of the resulting definition.
> + */
> +#define RTE_BITSET_DECLARE(name, size)		\
> +	uint64_t name[RTE_BITSET_NUM_WORDS(size)]
> +
> +/* XXX: should one include flags here and use to avoid a comparison? */
> +/* XXX: would this be better off as a function? */
> +
> +#define __RTE_BITSET_FOREACH_LEFT(var, size, start_bit, len)	\
> +	((len) - 1 - ((var) >= (start_bit) ? (var) - (start_bit) :	\
> +		  (size) - (start_bit) + (var)))
> +
> +#define __RTE_BITSET_FOREACH(var, bitset, size, start_bit, len, flags) \
> +	for ((var) = __rte_bitset_find(bitset, size, start_bit, len, \
> +				       flags);				\
> +	     (var) != -1;						\
> +	     (var) = __RTE_BITSET_FOREACH_LEFT(var, size, start_bit, \
> +					       len) > 0	?		\
> +		     __rte_bitset_find(bitset, size,		\
> +				       ((var) + 1) % (size),	\
> +				       __RTE_BITSET_FOREACH_LEFT(var,	\
> +								 size, \
> +								 start_bit, \
> +								 len),	\
> +				       flags) : -1)
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Iterate over all bits set.
> + *
> + * This macro iterates over all bits set (i.e., all ones) in the
> + * bitset, in the forward direction (i.e., starting with the least
> + * significant '1').
> + *
> + * @param var
> + *   An iterator variable of type @c ssize_t. For each sucessive iteration,
> + *   this variable will hold the bit index of a set bit.
> + * @param bitset
> + *   A <tt>const uint64_t *</tt> pointer to the bitset array.
> + * @param size
> + *   The size of the bitset (in bits).
> + */
> +
> +#define RTE_BITSET_FOREACH_SET(var, bitset, size)			\
> +	__RTE_BITSET_FOREACH(var, bitset, size, 0, size, 0)
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Iterate over all bits cleared.
> + *
> + * This macro iterates over all bits cleared in the bitset, in the
> + * forward direction (i.e., starting with the lowest-indexed set bit).
> + *
> + * @param var
> + *   An iterator variable of type @c ssize_t. For each successive iteration,
> + *   this variable will hold the bit index of a cleared bit.
> + * @param bitset
> + *   A <tt>const uint64_t *</tt> pointer to the bitset array.
> + * @param size
> + *   The size of the bitset (in bits).
> + */
> +
> +#define RTE_BITSET_FOREACH_CLEAR(var, bitset, size)			\
> +	__RTE_BITSET_FOREACH(var, bitset, size, 0, size,	\
> +			     __RTE_BITSET_FIND_FLAG_FIND_CLEAR)
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Iterate over all bits set within a range.
> + *
> + * This macro iterates over all bits set (i.e., all ones) in the
> + * specified range, in the forward direction (i.e., starting with the
> + * least significant '1').
> + *
> + * @param var
> + *   An iterator variable of type @c ssize_t. For each sucessive iteration,
> + *   this variable will hold the bit index of a set bit.
> + * @param bitset
> + *   A <tt>const uint64_t *</tt> pointer to the bitset array.
> + * @param size
> + *   The size of the bitset (in bits).
> + * @param start_bit
> + *   The index of the first bit to check. Must be less than @c size.
> + * @param len
> + *   The length (in bits) of the range. @c start_bit + @c len must be less
> + *   than or equal to @c size.
> + */
> +
> +#define RTE_BITSET_FOREACH_SET_RANGE(var, bitset, size, start_bit, \
> +				     len)			       \
> +	__RTE_BITSET_FOREACH(var, bitset, size, start_bit, len, 0)
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Iterate over all cleared bits within a range.
> + *
> + * This macro iterates over all bits cleared (i.e., all zeroes) in the
> + * specified range, in the forward direction (i.e., starting with the
> + * least significant '0').
> + *
> + * @param var
> + *   An iterator variable of type @c ssize_t. For each sucessive iteration,
> + *   this variable will hold the bit index of a set bit.
> + * @param bitset
> + *   A <tt>const uint64_t *</tt> pointer to the bitset array.
> + * @param size
> + *   The size of the bitset (in bits).
> + * @param start_bit
> + *   The index of the first bit to check. Must be less than @c size.
> + * @param len
> + *   The length (in bits) of the range. @c start_bit + @c len must be less
> + *   than or equal to @c size.
> + */
> +
> +#define RTE_BITSET_FOREACH_CLEAR_RANGE(var, bitset, size, start_bit,	\
> +				       len)				\
> +	__RTE_BITSET_FOREACH(var, bitset, size, start_bit, len,	\
> +			     __RTE_BITSET_FIND_FLAG_FIND_CLEAR)
> +
> +#define RTE_BITSET_FOREACH_SET_WRAP(var, bitset, size, start_bit,  \
> +				    len)			       \
> +	__RTE_BITSET_FOREACH(var, bitset, size, start_bit, len,    \
> +			     __RTE_BITSET_FIND_FLAG_WRAP)
> +
> +#define RTE_BITSET_FOREACH_CLEAR_WRAP(var, bitset, size, start_bit, \
> +				       len)				\
> +	__RTE_BITSET_FOREACH(var, bitset, size, start_bit, len,	\
> +			     __RTE_BITSET_FIND_FLAG_WRAP |		\
> +			     __RTE_BITSET_FIND_FLAG_FIND_CLEAR)
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Initializes a bitset.
> + *
> + * All bits are cleared.
> + *
> + * @param bitset
> + *   A pointer to the array of bitset 64-bit words.
> + * @param size
> + *   The size of the bitset (in bits).
> + */
> +
> +__rte_experimental
> +static inline void
> +rte_bitset_init(uint64_t *bitset, size_t size)
> +{
> +	memset(bitset, 0, RTE_BITSET_SIZE(size));
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Set a bit in the bitset.
> + *
> + * Bits are numbered from 0 to (size - 1) (inclusive).
> + *
> + * @param bitset
> + *   A pointer to the array words making up the bitset.
> + * @param bit_num
> + *   The index of the bit to be set.
> + */
> +
> +__rte_experimental
> +static inline void
> +rte_bitset_set(uint64_t *bitset, size_t bit_num)
> +{
> +	size_t word;
> +	size_t offset;
> +	uint64_t mask;
> +
> +	word = __RTE_BITSET_WORD_IDX(bit_num);
> +	offset = __RTE_BITSET_BIT_OFFSET(bit_num);
> +	mask = UINT64_C(1) << offset;
> +
> +	bitset[word] |= mask;
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Clear a bit in the bitset.
> + *
> + * Bits are numbered 0 to (size - 1) (inclusive).
> + *
> + * @param bitset
> + *   A pointer to the array words making up the bitset.
> + * @param bit_num
> + *   The index of the bit to be cleared.
> + */
> +
> +__rte_experimental
> +static inline void
> +rte_bitset_clear(uint64_t *bitset, size_t bit_num)
> +{
> +	size_t word;
> +	size_t offset;
> +	uint64_t mask;
> +
> +	word = __RTE_BITSET_WORD_IDX(bit_num);
> +	offset = __RTE_BITSET_BIT_OFFSET(bit_num);
> +	mask = ~(UINT64_C(1) << offset);
> +
> +	bitset[word] &= mask;
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Set all bits in the bitset.
> + *
> + * @param bitset
> + *   A pointer to the array of words making up the bitset.
> + * @param size
> + *   The size of the bitset (in bits).
> + */
> +
> +__rte_experimental
> +static inline void
> +rte_bitset_set_all(uint64_t *bitset, size_t size)
> +{
> +	memset(bitset, 0xFF, RTE_BITSET_SIZE(size));
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Clear all bits in the bitset.
> + *
> + * @param bitset
> + *   A pointer to the array of words making up the bitset.
> + * @param size
> + *   The size of the bitset (in bits).
> + */
> +
> +__rte_experimental
> +static inline void
> +rte_bitset_clear_all(uint64_t *bitset, size_t size)
> +{
> +	rte_bitset_init(bitset, size);
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Count all set bits.
> + *
> + * @param bitset
> + *   A pointer to the array of words making up the bitset.
> + * @param size
> + *   The size of the bitset (in bits).
> + * @return
> + *   Returns the number of '1' bits in the bitset.
> + */
> +
> +__rte_experimental
> +static inline size_t
> +rte_bitset_count_set(const uint64_t *bitset, size_t size)
> +{
> +	size_t i;
> +	size_t total = 0;
> +	uint64_t unused_mask;
> +
> +	/*
> +	 * Unused bits in a rte_bitset are always '0', and thus are
> +	 * not included in this count.
> +	 */
> +	for (i = 0; i < RTE_BITSET_NUM_WORDS(size) - 1; i++)
> +		total += __builtin_popcountll(bitset[i]);
> +
> +	unused_mask = UINT64_MAX >> __RTE_BITSET_UNUSED(size);
> +	total += __builtin_popcountll(bitset[i] & unused_mask);
> +
> +	return total;
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Count all cleared bits.
> + *
> + * @param bitset
> + *   A pointer to the array of words making up the bitset.
> + * @param size
> + *   The size of the bitset (in bits).
> + * @return
> + *   Returns the number of '0' bits in the bitset.
> + */
> +
> +__rte_experimental
> +static inline size_t
> +rte_bitset_count_clear(const uint64_t *bitset, size_t size)
> +{
> +	return size - rte_bitset_count_set(bitset, size);
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Test if a bit is set.
> + *
> + * @param bitset
> + *   A pointer to the array of words making up the bitset.
> + * @param bit_num
> + *   Index of the bit to test. Index 0 is the least significant bit.
> + * @return
> + *   Returns true if the bit is '1', and false if the bit is '0'.
> + */
> +
> +__rte_experimental
> +static inline bool
> +rte_bitset_test(const uint64_t *bitset, size_t bit_num)
> +{
> +	size_t word;
> +	size_t offset;
> +
> +	word = __RTE_BITSET_WORD_IDX(bit_num);
> +	offset = __RTE_BITSET_BIT_OFFSET(bit_num);
> +
> +	return (bitset[word] >> offset) & 1;
> +}
> +
> +#define __RTE_BITSET_FIND_FLAG_FIND_CLEAR (1U << 0)
> +#define __RTE_BITSET_FIND_FLAG_WRAP (1U << 1)
> +
> +__rte_experimental
> +static inline ssize_t
> +__rte_bitset_find_nowrap(const uint64_t *bitset, size_t __rte_unused size,
> +			 size_t start_bit, size_t len, bool find_clear)

   ^^ seems like the intent here is for this to be internal (not part of
      public api) i wonder do we have to mark it __rte_experimental?

      or better can we prevent visibility / consumption outside of the
      inline functions in this header?

> +{
> +	size_t word_idx;
> +	size_t offset;
> +	size_t end_bit = start_bit + len;
> +
> +	RTE_ASSERT(end_bit <= size);
> +
> +	if (unlikely(len == 0))
> +		return -1;
> +
> +	word_idx = __RTE_BITSET_WORD_IDX(start_bit);
> +	offset = __RTE_BITSET_BIT_OFFSET(start_bit);
> +
> +	while (word_idx <= __RTE_BITSET_WORD_IDX(end_bit - 1)) {
> +		uint64_t word;
> +		int word_ffs;
> +
> +		word = bitset[word_idx];
> +		if (find_clear)
> +			word = ~word;
> +
> +		word >>= offset;
> +
> +		word_ffs = __builtin_ffsll(word);
> +
> +		if (word_ffs != 0) {
> +			ssize_t ffs = start_bit + word_ffs - 1;
> +
> +			/*
> +			 * Check if set bit were among the last,
> +			 * unused bits, in the last word.
> +			 */
> +			if (unlikely(ffs >= (ssize_t)end_bit))
> +				return -1;
> +
> +			return ffs;
> +		}
> +
> +		start_bit += (RTE_BITSET_WORD_BITS - offset);
> +		word_idx++;
> +		offset = 0;
> +	}
> +
> +	return -1;
> +
> +}
> +