Add dynamic_bitset (#352)

This PR adds `dynamic_bitset` code that will be used in Trie data
structure. Trie will be integrated in a separate PR #350.

Since `dynamic_bitset` is not intended to be part of public-facing API,
all files (.cuh and .inl) are located in
include/cuco/detail/trie/dynamic_bitset

Tests are added in tests/dynamic_bitset

---------

Co-authored-by: Yunsong Wang <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/cuco/detail/trie/dynamic_bitset/dynamic_bitset.cuh

@@ -0,0 +1,375 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2023 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cuco/cuda_stream_ref.hpp>
+
+#include <thrust/device_malloc_allocator.h>
+#include <thrust/device_vector.h>
+
+#include <cuda/std/array>
+
+#include <climits>
+#include <cstddef>
+
+namespace cuco {
+namespace experimental {
+namespace detail {
+
+/**
+ * @brief Struct to store ranks of bits at 256-bit intervals (or blocks)
+ *
+ * This struct encodes a list of four rank values using base + offset format
+ * e.g. [1000, 1005, 1006, 1009] is stored as base = 1000, offsets = [5, 6, 9]
+ * base uses 40 bits, split between one uint32_t and one uint8_t
+ * each offset uses 8 bits
+ */
+struct rank {
+  uint32_t base_hi_;                      ///< Upper 32 bits of base
+  uint8_t base_lo_;                       ///< Lower 8 bits of base
+  cuda::std::array<uint8_t, 3> offsets_;  ///< Offsets for 64-bit sub-intervals, relative to base
+
+  /**
+   * @brief Gets base rank of current 256-bit interval
+   *
+   * @return The base rank
+   */
+  __host__ __device__ constexpr uint64_t base() const noexcept
+  {
+    return (static_cast<uint64_t>(base_hi_) << CHAR_BIT) | base_lo_;
+  }
+
+  /**
+   * @brief Sets base rank of current 256-bit interval
+   *
+   * @param base Base rank
+   */
+  __host__ __device__ constexpr void set_base(uint64_t base) noexcept
+  {
+    base_hi_ = static_cast<uint32_t>(base >> CHAR_BIT);
+    base_lo_ = static_cast<uint8_t>(base);
+  }
+};
+
+/**
+ * @brief Bitset class with rank and select index structures
+ *
+ * In addition to standard bitset set/test operations, this class provides
+ * rank and select operation API. It maintains index structures to make both these
+ * new operations close to constant time.
+ *
+ * Current limitations:
+ * - Stream controls are partially supported due to the use of `thrust::device_vector` as storage
+ * - Device ref doesn't support modifiers like `set`, `reset`, etc.
+ *
+ * @tparam Allocator Type of allocator used for device storage
+ */
+// TODO: have to use device_malloc_allocator for now otherwise the container cannot grow
+template <class Allocator = thrust::device_malloc_allocator<std::byte>>
+class dynamic_bitset {
+ public:
+  using size_type = std::size_t;  ///< size type to specify bit index
+  using word_type = uint64_t;     ///< word type
+  /// Type of the allocator to (de)allocate words
+  using allocator_type = typename std::allocator_traits<Allocator>::rebind_alloc<word_type>;
+
+  /// Number of bits per block. Note this is a tradeoff between space efficiency and perf.
+  static constexpr size_type words_per_block = 4;
+  /// Number of bits in a word
+  static constexpr size_type bits_per_word = sizeof(word_type) * CHAR_BIT;
+  /// Number of bits in a block
+  static constexpr size_type bits_per_block = words_per_block * bits_per_word;
+
+  /**
+   * @brief Constructs an empty bitset
+   *
+   * @param allocator Allocator used for allocating device storage
+   */
+  constexpr dynamic_bitset(Allocator const& allocator = Allocator{});
+
+  /**
+   * @brief Appends the given element `value` to the end of the bitset
+   *
+   * This API may involve data reallocation if the current storage is exhausted.
+   *
+   * @param value Boolean value of the new bit to be added
+   */
+  constexpr void push_back(bool value) noexcept;
+
+  /**
+   * @brief Sets the target bit indexed by `index` to a specified `value`.
+   *
+   * @param index Position of bit to be modified
+   * @param value New value of the target bit
+   */
+  constexpr void set(size_type index, bool value) noexcept;
+
+  /**
+   * @brief Sets the last bit to a specified value
+   *
+   * @param value New value of the last bit
+   */
+  constexpr void set_last(bool value) noexcept;
+
+  /**
+   * @brief For any element `keys_begin[i]` in the range `[keys_begin, keys_end)`, stores the
+   * boolean value at position `keys_begin[i]` to `output_begin[i]`.
+   *
+   * @tparam KeyIt Device-accessible iterator whose `value_type` can be converted to bitset's
+   * `size_type`
+   * @tparam OutputIt Device-accessible iterator whose `value_type` can be constructed from boolean
+   * type
+   *
+   * @param keys_begin Begin iterator to keys list whose values are queried
+   * @param keys_end End iterator to keys list
+   * @param outputs_begin Begin iterator to outputs of test operation
+   * @param stream Stream to execute test kernel
+   */
+  template <typename KeyIt, typename OutputIt>
+  constexpr void test(KeyIt keys_begin,
+                      KeyIt keys_end,
+                      OutputIt outputs_begin,
+                      cuda_stream_ref stream = {}) noexcept;
+
+  /**
+   * @brief For any element `keys_begin[i]` in the range `[keys_begin, keys_end)`, stores total
+   * count of `1` bits preceeding (but not including) position `keys_begin[i]` to `output_begin[i]`.
+   *
+   * @tparam KeyIt Device-accessible iterator whose `value_type` can be converted to bitset's
+   * `size_type`
+   * @tparam OutputIt Device-accessible iterator whose `value_type` can be constructed from bitset's
+   * `size_type`
+   *
+   * @param keys_begin Begin iterator to keys list whose ranks are queried
+   * @param keys_end End iterator to keys list
+   * @param outputs_begin Begin iterator to outputs ranks list
+   * @param stream Stream to execute ranks kernel
+   */
+  template <typename KeyIt, typename OutputIt>
+  constexpr void rank(KeyIt keys_begin,
+                      KeyIt keys_end,
+                      OutputIt outputs_begin,
+                      cuda_stream_ref stream = {}) noexcept;
+
+  /**
+   * @brief For any element `keys_begin[i]` in the range `[keys_begin, keys_end)`, stores the
+   * position of `keys_begin[i]`th `1` bit to `output_begin[i]`.
+   *
+   * @tparam KeyIt Device-accessible iterator whose `value_type` can be converted to bitset's
+   * `size_type`
+   * @tparam OutputIt Device-accessible iterator whose `value_type` can be constructed from bitset's
+   * `size_type`
+   *
+   * @param keys_begin Begin iterator to keys list whose select values are queried
+   * @param keys_end End iterator to keys list
+   * @param outputs_begin Begin iterator to outputs selects list
+   * @param stream Stream to execute selects kernel
+   */
+  template <typename KeyIt, typename OutputIt>
+  constexpr void select(KeyIt keys_begin,
+                        KeyIt keys_end,
+                        OutputIt outputs_begin,
+                        cuda_stream_ref stream = {}) noexcept;
+
+  using rank_type = cuco::experimental::detail::rank;  ///< Rank type
+
+  /**
+   *@brief Struct to hold all storage refs needed by reference
+   */
+  // TODO: this is not a real ref type, to be changed
+  struct storage_ref_type {
+    const word_type* words_ref_;  ///< Words ref
+
+    const rank_type* ranks_true_ref_;    ///< Ranks ref for 1 bits
+    const size_type* selects_true_ref_;  ///< Selects ref for 1 bits
+
+    const rank_type* ranks_false_ref_;    ///< Ranks ref for 0 bits
+    const size_type* selects_false_ref_;  ///< Selects ref 0 bits
+  };
+
+  /**
+   * @brief Device non-owning reference type of dynamic_bitset
+   */
+  class reference {
+   public:
+    /**
+     * @brief Constructs a reference
+     *
+     * @param storage Struct with non-owning refs to bitset storage arrays
+     */
+    __host__ __device__ explicit constexpr reference(storage_ref_type storage) noexcept;
+
+    /**
+     * @brief Access value of a single bit
+     *
+     * @param key Position of bit
+     *
+     * @return Value of bit at position specified by key
+     */
+    [[nodiscard]] __device__ constexpr bool test(size_type key) const noexcept;
+
+    /**
+     * @brief Access a single word of internal storage
+     *
+     * @param word_id Index of word
+     *
+     * @return Word at position specified by index
+     */
+    [[nodiscard]] __device__ constexpr word_type word(size_type word_id) const noexcept;
+
+    /**
+     * @brief Find position of first set bit starting from a given position (inclusive)
+     *
+     * @param key Position of starting bit
+     *
+     * @return Index of next set bit
+     */
+    [[nodiscard]] __device__ size_type find_next(size_type key) const noexcept;
+
+    /**
+     * @brief Find number of set bits (rank) in all positions before the input position (exclusive)
+     *
+     * @param key Input bit position
+     *
+     * @return Rank of input position
+     */
+    [[nodiscard]] __device__ constexpr size_type rank(size_type key) const noexcept;
+
+    /**
+     * @brief Find position of Nth set (1) bit counting from start
+     *
+     * @param count Input N
+     *
+     * @return Position of Nth set bit
+     */
+    [[nodiscard]] __device__ constexpr size_type select(size_type count) const noexcept;
+
+    /**
+     * @brief Find position of Nth not-set (0) bit counting from start
+     *
+     * @param count Input N
+     *
+     * @return Position of Nth not-set bit
+     */
+    [[nodiscard]] __device__ constexpr size_type select_false(size_type count) const noexcept;
+
+   private:
+    /**
+     * @brief Helper function for select operation that computes an initial rank estimate
+     *
+     * @param count Input count for which select operation is being performed
+     * @param selects Selects array
+     * @param ranks Ranks array
+     *
+     * @return index in ranks which corresponds to highest rank less than count (least upper bound)
+     */
+    template <typename SelectsRef, typename RanksRef>
+    [[nodiscard]] __device__ constexpr size_type initial_rank_estimate(
+      size_type count, const SelectsRef& selects, const RanksRef& ranks) const noexcept;
+
+    /**
+     * @brief Subtract rank estimate from input count and return an increment to word_id
+     *
+     * @tparam Rank type
+     *
+     * @param count Input count that will be updated
+     * @param rank  Initial rank estimate for count
+     *
+     * @return Increment to word_id based on rank values
+     */
+    template <typename Rank>
+    [[nodiscard]] __device__ constexpr size_type subtract_rank_from_count(size_type& count,
+                                                                          Rank rank) const noexcept;
+
+    /**
+     * @brief Find position of Nth set bit in a 64-bit word
+     *
+     * @param N Input count
+     *
+     * @return Position of Nth set bit
+     */
+    [[nodiscard]] __device__ size_type select_bit_in_word(size_type N,
+                                                          word_type word) const noexcept;
+
+    storage_ref_type storage_;  ///< Non-owning storage
+  };
+
+  using ref_type = reference;  ///< Non-owning container ref type
+
+  /**
+   * @brief Gets non-owning device ref of the current object
+   *
+   * @return Device ref of the current `dynamic_bitset` object
+   */
+  [[nodiscard]] constexpr ref_type ref() const noexcept;
+
+  /**
+   * @brief Gets the number of bits dynamic_bitset holds
+   *
+   * @return Number of bits dynamic_bitset holds
+   */
+  [[nodiscard]] constexpr size_type size() const noexcept;
+
+ private:
+  /// Type of the allocator to (de)allocate ranks
+  using rank_allocator_type = typename std::allocator_traits<Allocator>::rebind_alloc<rank_type>;
+  /// Type of the allocator to (de)allocate indices
+  using size_allocator_type = typename std::allocator_traits<Allocator>::rebind_alloc<size_type>;
+
+  allocator_type allocator_;  ///< Words allocator
+  size_type n_bits_;          ///< Number of bits dynamic_bitset currently holds
+  bool is_built_;  ///< Flag indicating whether the rank and select indices are built or not
+
+  /// Words vector that represents all bits
+  thrust::device_vector<word_type, allocator_type> words_;
+  /// Rank values for every 256-th bit (4-th word)
+  thrust::device_vector<rank_type, rank_allocator_type> ranks_true_;
+  /// Same as ranks_ but for `0` bits
+  thrust::device_vector<rank_type, rank_allocator_type> ranks_false_;
+  /// Block indices of (0, 256, 512...)th `1` bit
+  thrust::device_vector<size_type, size_allocator_type> selects_true_;
+  /// Same as selects_, but for `0` bits
+  thrust::device_vector<size_type, size_allocator_type> selects_false_;
+
+  /**
+   * @brief Builds indexes for rank and select
+   *
+   * @param stream Stream to execute kernels
+   */
+  constexpr void build(cuda_stream_ref stream = {}) noexcept;
+
+  /**
+   * @brief Populates rank and select indexes for true or false bits
+   *
+   * @param ranks Output array of ranks
+   * @param selects Output array of selects
+   * @param flip_bits If true, negate bits to construct indexes for false bits
+   * @param stream Stream to execute kernels
+   */
+  constexpr void build_ranks_and_selects(
+    thrust::device_vector<rank_type, rank_allocator_type>& ranks,
+    thrust::device_vector<size_type, size_allocator_type>& selects,
+    bool flip_bits,
+    cuda_stream_ref stream = {});
+};
+
+}  // namespace detail
+}  // namespace experimental
+}  // namespace cuco
+
+#include <cuco/detail/trie/dynamic_bitset/dynamic_bitset.inl>