BLI_index_mask.hh

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#pragma once
 
#include <array>
#include <limits>
#include <optional>
#include <variant>
 
#include "BLI_bit_span.hh"
#include "BLI_function_ref.hh"
#include "BLI_index_mask_fwd.hh"
#include "BLI_index_ranges_builder_fwd.hh"
#include "BLI_linear_allocator.hh"
#include "BLI_offset_span.hh"
#include "BLI_task.hh"
#include "BLI_unique_sorted_indices.hh"
#include "BLI_vector.hh"
#include "BLI_vector_set.hh"
#include "BLI_virtual_array_fwd.hh"
 
namespace blender::index_mask {
 
static constexpr int64_t max_segment_size_shift = 14;
static constexpr int64_t max_segment_size = (1 << max_segment_size_shift); /* 16384 */
static constexpr int64_t max_segment_size_mask_low = max_segment_size - 1;
static constexpr int64_t max_segment_size_mask_high = ~max_segment_size_mask_low;
 
struct RawMaskIterator {
  int64_t segment_i;
  int16_t index_in_segment;
};
 
struct IndexMaskData {
  int64_t indices_num_;
  int64_t segments_num_;
  const int16_t **indices_by_segment_;
  const int64_t *segment_offsets_;
  const int64_t *cumulative_segment_sizes_;
  int64_t begin_index_in_segment_;
  int64_t end_index_in_segment_;
};
 
class IndexMaskMemory : public LinearAllocator<> {
 private:
  AlignedBuffer<1024, 8> inline_buffer_;
 
 public:
  IndexMaskMemory()
  {
    this->provide_buffer(inline_buffer_);
  }
};
 
class IndexMaskSegment : public OffsetSpan<int64_t, int16_t> {
 public:
  using OffsetSpan<int64_t, int16_t>::OffsetSpan;
 
  explicit IndexMaskSegment(const OffsetSpan<int64_t, int16_t> span);
 
  IndexMaskSegment slice(const IndexRange &range) const;
  IndexMaskSegment slice(const int64_t start, const int64_t size) const;
 
  IndexMaskSegment shift(const int64_t shift) const;
};
 
class IndexMask : private IndexMaskData {
 public:
  IndexMask();
  explicit IndexMask(int64_t size);
  IndexMask(IndexRange range);
 
  template<typename T> static IndexMask from_indices(Span<T> indices, IndexMaskMemory &memory);
  static IndexMask from_bits(BitSpan bits, IndexMaskMemory &memory);
  static IndexMask from_bits(const IndexMask &universe, BitSpan bits, IndexMaskMemory &memory);
  static IndexMask from_bools(Span<bool> bools, IndexMaskMemory &memory);
  static IndexMask from_bools(const VArray<bool> &bools, IndexMaskMemory &memory);
  static IndexMask from_bools(const IndexMask &universe,
                              Span<bool> bools,
                              IndexMaskMemory &memory);
  static IndexMask from_bools_inverse(const IndexMask &universe,
                                      Span<bool> bools,
                                      IndexMaskMemory &memory);
  static IndexMask from_bools(const IndexMask &universe,
                              const VArray<bool> &bools,
                              IndexMaskMemory &memory);
  static IndexMask from_repeating(const IndexMask &mask_to_repeat,
                                  int64_t repetitions,
                                  int64_t stride,
                                  int64_t initial_offset,
                                  IndexMaskMemory &memory);
  static IndexMask from_every_nth(int64_t n,
                                  int64_t indices_num,
                                  const int64_t initial_offset,
                                  IndexMaskMemory &memory);
  static IndexMask from_segments(Span<IndexMaskSegment> segments, IndexMaskMemory &memory);
  using Initializer = std::variant<IndexRange, Span<int64_t>, Span<int>, int64_t>;
  static IndexMask from_initializers(const Span<Initializer> initializers,
                                     IndexMaskMemory &memory);
  static IndexMask from_union(const IndexMask &mask_a,
                              const IndexMask &mask_b,
                              IndexMaskMemory &memory);
  static IndexMask from_difference(const IndexMask &mask_a,
                                   const IndexMask &mask_b,
                                   IndexMaskMemory &memory);
  static IndexMask from_intersection(const IndexMask &mask_a,
                                     const IndexMask &mask_b,
                                     IndexMaskMemory &memory);
  template<typename Fn>
  static IndexMask from_predicate(const IndexMask &universe,
                                  GrainSize grain_size,
                                  IndexMaskMemory &memory,
                                  Fn &&predicate);
  static IndexMask from_batch_predicate(
      const IndexMask &universe,
      GrainSize grain_size,
      IndexMaskMemory &memory,
      FunctionRef<int64_t(const IndexMaskSegment &universe_segment,
                          IndexRangesBuilder<int16_t> &builder)> batch_predicate);
  template<typename T, typename Fn>
  static void from_groups(const IndexMask &universe,
                          IndexMaskMemory &memory,
                          Fn &&get_group_index,
                          MutableSpan<IndexMask> r_masks);
 
  static Vector<IndexMask, 4> from_group_ids(const VArray<int> &group_ids,
                                             IndexMaskMemory &memory,
                                             VectorSet<int> &r_index_by_group_id);
  static Vector<IndexMask, 4> from_group_ids(const IndexMask &universe,
                                             const VArray<int> &group_ids,
                                             IndexMaskMemory &memory,
                                             VectorSet<int> &r_index_by_group_id);
 
  int64_t size() const;
  bool is_empty() const;
  IndexRange index_range() const;
  int64_t first() const;
  int64_t last() const;
 
  IndexRange bounds() const;
 
  int64_t min_array_size() const;
 
  std::optional<RawMaskIterator> find(int64_t query_index) const;
  std::optional<RawMaskIterator> find_larger_equal(int64_t query_index) const;
  std::optional<RawMaskIterator> find_smaller_equal(int64_t query_index) const;
  bool contains(int64_t query_index) const;
 
  RawMaskIterator index_to_iterator(int64_t index) const;
  int64_t iterator_to_index(const RawMaskIterator &it) const;
 
  int64_t operator[](int64_t i) const;
  int64_t operator[](const RawMaskIterator &it) const;
 
  IndexMask slice(IndexRange range) const;
  IndexMask slice(int64_t start, int64_t size) const;
  IndexMask slice(RawMaskIterator first_it, RawMaskIterator last_it, int64_t size) const;
  IndexMask slice_content(IndexRange range) const;
  IndexMask slice_content(int64_t start, int64_t size) const;
  IndexMask slice_and_shift(IndexRange range, int64_t offset, IndexMaskMemory &memory) const;
  IndexMask slice_and_shift(int64_t start,
                            int64_t size,
                            int64_t offset,
                            IndexMaskMemory &memory) const;
 
  IndexMask shift(const int64_t offset, IndexMaskMemory &memory) const;
 
  IndexMask complement(const IndexMask &universe, IndexMaskMemory &memory) const;
 
  int64_t segments_num() const;
  IndexMaskSegment segment(int64_t segment_i) const;
 
  static void foreach_segment_zipped(Span<IndexMask> masks,
                                     FunctionRef<bool(Span<IndexMaskSegment> segments)> fn);
 
  template<typename Fn> void foreach_index(Fn &&fn) const;
  template<typename Fn> void foreach_index(GrainSize grain_size, Fn &&fn) const;
 
  template<typename IndexT, typename Fn> void foreach_index_optimized(Fn &&fn) const;
  template<typename IndexT, typename Fn>
  void foreach_index_optimized(GrainSize grain_size, Fn &&fn) const;
 
  template<typename Fn> void foreach_segment(Fn &&fn) const;
  template<typename Fn> void foreach_segment(GrainSize grain_size, Fn &&fn) const;
 
  template<typename Fn> void foreach_segment_optimized(Fn &&fn) const;
  template<typename Fn> void foreach_segment_optimized(GrainSize grain_size, Fn &&fn) const;
 
  template<typename Fn> void foreach_range(Fn &&fn) const;
 
  template<typename T> void to_indices(MutableSpan<T> r_indices) const;
  void set_bits(MutableBitSpan r_bits, int64_t offset = 0) const;
  void to_bits(MutableBitSpan r_bits, int64_t offset = 0) const;
  void to_bools(MutableSpan<bool> r_bools) const;
  std::optional<IndexRange> to_range() const;
  Vector<IndexRange> to_ranges() const;
  Vector<IndexRange> to_ranges_invert(IndexRange universe) const;
  template<int64_t N = 4>
  Vector<std::variant<IndexRange, IndexMaskSegment>, N> to_spans_and_ranges() const;
 
  IndexMaskData &data_for_inplace_construction();
 
  friend bool operator==(const IndexMask &a, const IndexMask &b);
  friend bool operator!=(const IndexMask &a, const IndexMask &b);
};
 
class IndexMaskFromSegment : NonCopyable, NonMovable {
 private:
  int64_t segment_offset_;
  const int16_t *segment_indices_;
  std::array<int64_t, 2> cumulative_segment_sizes_;
  IndexMask mask_;
 
 public:
  IndexMaskFromSegment();
  const IndexMask &update(IndexMaskSegment segment);
};
 
inline IndexMaskFromSegment::IndexMaskFromSegment()
{
  IndexMaskData &data = mask_.data_for_inplace_construction();
  cumulative_segment_sizes_[0] = 0;
  data.segments_num_ = 1;
  data.indices_by_segment_ = &segment_indices_;
  data.segment_offsets_ = &segment_offset_;
  data.cumulative_segment_sizes_ = cumulative_segment_sizes_.data();
  data.begin_index_in_segment_ = 0;
}
 
inline const IndexMask &IndexMaskFromSegment::update(const IndexMaskSegment segment)
{
  const Span<int16_t> indices = segment.base_span();
  BLI_assert(!indices.is_empty());
  BLI_assert(std::is_sorted(indices.begin(), indices.end()));
  BLI_assert(indices[0] >= 0);
  BLI_assert(indices.last() < max_segment_size);
  const int64_t indices_num = indices.size();
 
  IndexMaskData &data = mask_.data_for_inplace_construction();
  segment_offset_ = segment.offset();
  segment_indices_ = indices.data();
  cumulative_segment_sizes_[1] = int16_t(indices_num);
  data.indices_num_ = indices_num;
  data.end_index_in_segment_ = indices_num;
 
  return mask_;
}
 
std::array<int16_t, max_segment_size> build_static_indices_array();
const IndexMask &get_static_index_mask_for_min_size(const int64_t min_size);
std::ostream &operator<<(std::ostream &stream, const IndexMask &mask);
 
/* -------------------------------------------------------------------- */
inline const std::array<int16_t, max_segment_size> &get_static_indices_array()
{
  alignas(64) static const std::array<int16_t, max_segment_size> data =
      build_static_indices_array();
  return data;
}
 
template<typename T>
inline void masked_fill(MutableSpan<T> data, const T &value, const IndexMask &mask)
{
  mask.foreach_index_optimized<int64_t>([&](const int64_t i) { data[i] = value; });
}
 
template<typename T> void build_reverse_map(const IndexMask &mask, MutableSpan<T> r_map);
 
int64_t consolidate_index_mask_segments(MutableSpan<IndexMaskSegment> segments,
                                        IndexMaskMemory &memory);
 
/* -------------------------------------------------------------------- */
inline bool operator!=(const RawMaskIterator &a, const RawMaskIterator &b)
{
  return a.segment_i != b.segment_i || a.index_in_segment != b.index_in_segment;
}
 
inline bool operator==(const RawMaskIterator &a, const RawMaskIterator &b)
{
  return !(a != b);
}
 
/* -------------------------------------------------------------------- */
inline IndexMaskSegment::IndexMaskSegment(const OffsetSpan<int64_t, int16_t> span)
    : OffsetSpan<int64_t, int16_t>(span)
{
}
 
inline IndexMaskSegment IndexMaskSegment::slice(const IndexRange &range) const
{
  return IndexMaskSegment(static_cast<const OffsetSpan<int64_t, int16_t> *>(this)->slice(range));
}
 
inline IndexMaskSegment IndexMaskSegment::slice(const int64_t start, const int64_t size) const
{
  return IndexMaskSegment(
      static_cast<const OffsetSpan<int64_t, int16_t> *>(this)->slice(start, size));
}
 
inline IndexMaskSegment IndexMaskSegment::shift(const int64_t shift) const
{
  BLI_assert(this->is_empty() || (*this)[0] + shift >= 0);
  return IndexMaskSegment(this->offset() + shift, this->base_span());
}
 
/* -------------------------------------------------------------------- */
inline void init_empty_mask(IndexMaskData &data)
{
  static constexpr int64_t cumulative_sizes_for_empty_mask[1] = {0};
 
  data.indices_num_ = 0;
  data.segments_num_ = 0;
  data.cumulative_segment_sizes_ = cumulative_sizes_for_empty_mask;
  /* Intentionally leave some pointers uninitialized which must not be accessed on empty masks
   * anyway. */
}
 
inline IndexMask::IndexMask()
{
  init_empty_mask(*this);
}
 
inline IndexMask::IndexMask(const int64_t size)
{
  if (size == 0) {
    init_empty_mask(*this);
    return;
  }
  *this = get_static_index_mask_for_min_size(size);
  indices_num_ = size;
  segments_num_ = ((size + max_segment_size - 1) >> max_segment_size_shift);
  begin_index_in_segment_ = 0;
  end_index_in_segment_ = size - ((size - 1) & max_segment_size_mask_high);
}
 
inline IndexMask::IndexMask(const IndexRange range)
{
  if (range.is_empty()) {
    init_empty_mask(*this);
    return;
  }
  const int64_t one_after_last = range.one_after_last();
  *this = get_static_index_mask_for_min_size(one_after_last);
 
  const int64_t first_segment_i = range.first() >> max_segment_size_shift;
  const int64_t last_segment_i = range.last() >> max_segment_size_shift;
 
  indices_num_ = range.size();
  segments_num_ = last_segment_i - first_segment_i + 1;
  indices_by_segment_ += first_segment_i;
  segment_offsets_ += first_segment_i;
  cumulative_segment_sizes_ += first_segment_i;
  begin_index_in_segment_ = range.first() & max_segment_size_mask_low;
  end_index_in_segment_ = one_after_last - ((one_after_last - 1) & max_segment_size_mask_high);
}
 
inline int64_t IndexMask::size() const
{
  return indices_num_;
}
 
inline bool IndexMask::is_empty() const
{
  return indices_num_ == 0;
}
 
inline IndexRange IndexMask::index_range() const
{
  return IndexRange(indices_num_);
}
 
inline IndexRange IndexMask::bounds() const
{
  if (this->is_empty()) {
    return IndexRange();
  }
  const int64_t first = this->first();
  const int64_t last = this->last();
  return IndexRange::from_begin_end_inclusive(first, last);
}
 
inline int64_t IndexMask::first() const
{
  BLI_assert(indices_num_ > 0);
  return segment_offsets_[0] + indices_by_segment_[0][begin_index_in_segment_];
}
 
inline int64_t IndexMask::last() const
{
  BLI_assert(indices_num_ > 0);
  const int64_t last_segment_i = segments_num_ - 1;
  return segment_offsets_[last_segment_i] +
         indices_by_segment_[last_segment_i][end_index_in_segment_ - 1];
}
 
inline int64_t IndexMask::min_array_size() const
{
  if (indices_num_ == 0) {
    return 0;
  }
  return this->last() + 1;
}
 
inline RawMaskIterator IndexMask::index_to_iterator(const int64_t index) const
{
  BLI_assert(index >= 0);
  BLI_assert(index < indices_num_);
  RawMaskIterator it;
  const int64_t full_index = index + cumulative_segment_sizes_[0] + begin_index_in_segment_;
  it.segment_i = -1 +
                 binary_search::find_predicate_begin(
                     cumulative_segment_sizes_,
                     cumulative_segment_sizes_ + segments_num_ + 1,
                     [&](const int64_t cumulative_size) { return cumulative_size > full_index; });
  it.index_in_segment = full_index - cumulative_segment_sizes_[it.segment_i];
  return it;
}
 
inline int64_t IndexMask::iterator_to_index(const RawMaskIterator &it) const
{
  BLI_assert(it.segment_i >= 0);
  BLI_assert(it.segment_i < segments_num_);
  BLI_assert(it.index_in_segment >= 0);
  BLI_assert(it.index_in_segment < cumulative_segment_sizes_[it.segment_i + 1] -
                                       cumulative_segment_sizes_[it.segment_i]);
  return it.index_in_segment + cumulative_segment_sizes_[it.segment_i] -
         cumulative_segment_sizes_[0] - begin_index_in_segment_;
}
 
inline int64_t IndexMask::operator[](const int64_t i) const
{
  const RawMaskIterator it = this->index_to_iterator(i);
  return (*this)[it];
}
 
inline int64_t IndexMask::operator[](const RawMaskIterator &it) const
{
  return segment_offsets_[it.segment_i] + indices_by_segment_[it.segment_i][it.index_in_segment];
}
 
inline int64_t IndexMask::segments_num() const
{
  return segments_num_;
}
 
inline IndexMaskSegment IndexMask::segment(const int64_t segment_i) const
{
  BLI_assert(segment_i >= 0);
  BLI_assert(segment_i < segments_num_);
  const int64_t full_segment_size = cumulative_segment_sizes_[segment_i + 1] -
                                    cumulative_segment_sizes_[segment_i];
  const int64_t begin_index = (segment_i == 0) ? begin_index_in_segment_ : 0;
  const int64_t end_index = (segment_i == segments_num_ - 1) ? end_index_in_segment_ :
                                                               full_segment_size;
  const int64_t segment_size = end_index - begin_index;
  return IndexMaskSegment{segment_offsets_[segment_i],
                          {indices_by_segment_[segment_i] + begin_index, segment_size}};
}
 
inline IndexMask IndexMask::slice(const IndexRange range) const
{
  return this->slice(range.start(), range.size());
}
 
inline IndexMaskData &IndexMask::data_for_inplace_construction()
{
  return *this;
}
 
template<typename Fn>
constexpr bool has_segment_and_start_parameter =
    std::is_invocable_r_v<void, Fn, IndexMaskSegment, int64_t> ||
    std::is_invocable_r_v<void, Fn, IndexRange, int64_t>;
 
template<typename Fn> inline void IndexMask::foreach_index(Fn &&fn) const
{
  this->foreach_segment(
      [&](const IndexMaskSegment indices, [[maybe_unused]] const int64_t start_segment_pos) {
        if constexpr (std::is_invocable_r_v<void, Fn, int64_t, int64_t>) {
          for (const int64_t i : indices.index_range()) {
            fn(indices[i], start_segment_pos + i);
          }
        }
        else {
          for (const int64_t index : indices) {
            fn(index);
          }
        }
      });
}
 
template<typename Fn>
inline void IndexMask::foreach_index(const GrainSize grain_size, Fn &&fn) const
{
  threading::parallel_for(this->index_range(), grain_size.value, [&](const IndexRange range) {
    const IndexMask sub_mask = this->slice(range);
    sub_mask.foreach_index([&](const int64_t i, [[maybe_unused]] const int64_t index_pos) {
      if constexpr (std::is_invocable_r_v<void, Fn, int64_t, int64_t>) {
        fn(i, index_pos + range.start());
      }
      else {
        fn(i);
      }
    });
  });
}
 
template<typename T, typename Fn>
#if (defined(__GNUC__) && !defined(__clang__))
[[gnu::optimize("O3")]]
#endif
inline void
optimized_foreach_index(const IndexMaskSegment segment, const Fn fn)
{
  BLI_assert(segment.last() < std::numeric_limits<T>::max());
  if (unique_sorted_indices::non_empty_is_range(segment.base_span())) {
    const T start = T(segment[0]);
    const T last = T(segment.last());
    for (T i = start; i <= last; i++) {
      fn(i);
    }
  }
  else {
    for (const int64_t i : segment) {
      fn(T(i));
    }
  }
}
 
template<typename T, typename Fn>
#if (defined(__GNUC__) && !defined(__clang__))
[[gnu::optimize("O3")]]
#endif
inline void
optimized_foreach_index_with_pos(const IndexMaskSegment segment,
                                 const int64_t segment_pos,
                                 const Fn fn)
{
  BLI_assert(segment.last() < std::numeric_limits<T>::max());
  BLI_assert(segment.size() + segment_pos < std::numeric_limits<T>::max());
  if (unique_sorted_indices::non_empty_is_range(segment.base_span())) {
    const T start = T(segment[0]);
    const T last = T(segment.last());
    for (T i = start, pos = T(segment_pos); i <= last; i++, pos++) {
      fn(i, pos);
    }
  }
  else {
    T pos = T(segment_pos);
    for (const int64_t i : segment.index_range()) {
      const T index = T(segment[i]);
      fn(index, pos);
      pos++;
    }
  }
}
 
template<typename IndexT, typename Fn>
inline void IndexMask::foreach_index_optimized(Fn &&fn) const
{
  this->foreach_segment(
      [&](const IndexMaskSegment segment, [[maybe_unused]] const int64_t segment_pos) {
        if constexpr (std::is_invocable_r_v<void, Fn, IndexT, IndexT>) {
          optimized_foreach_index_with_pos<IndexT>(segment, segment_pos, fn);
        }
        else {
          optimized_foreach_index<IndexT>(segment, fn);
        }
      });
}
 
template<typename IndexT, typename Fn>
inline void IndexMask::foreach_index_optimized(const GrainSize grain_size, Fn &&fn) const
{
  threading::parallel_for(this->index_range(), grain_size.value, [&](const IndexRange range) {
    const IndexMask sub_mask = this->slice(range);
    sub_mask.foreach_segment(
        [&](const IndexMaskSegment segment, [[maybe_unused]] const int64_t segment_pos) {
          if constexpr (std::is_invocable_r_v<void, Fn, IndexT, IndexT>) {
            optimized_foreach_index_with_pos<IndexT>(segment, segment_pos + range.start(), fn);
          }
          else {
            optimized_foreach_index<IndexT>(segment, fn);
          }
        });
  });
}
 
template<typename Fn> inline void IndexMask::foreach_segment_optimized(Fn &&fn) const
{
  this->foreach_segment(
      [&](const IndexMaskSegment segment, [[maybe_unused]] const int64_t start_segment_pos) {
        if (unique_sorted_indices::non_empty_is_range(segment.base_span())) {
          const IndexRange range(segment[0], segment.size());
          if constexpr (has_segment_and_start_parameter<Fn>) {
            fn(range, start_segment_pos);
          }
          else {
            fn(range);
          }
        }
        else {
          if constexpr (has_segment_and_start_parameter<Fn>) {
            fn(segment, start_segment_pos);
          }
          else {
            fn(segment);
          }
        }
      });
}
 
template<typename Fn>
inline void IndexMask::foreach_segment_optimized(const GrainSize grain_size, Fn &&fn) const
{
  threading::parallel_for(this->index_range(), grain_size.value, [&](const IndexRange range) {
    const IndexMask sub_mask = this->slice(range);
    sub_mask.foreach_segment_optimized(
        [&fn, range_start = range.start()](const auto segment,
                                           [[maybe_unused]] const int64_t start_segment_pos) {
          if constexpr (has_segment_and_start_parameter<Fn>) {
            fn(segment, start_segment_pos + range_start);
          }
          else {
            fn(segment);
          }
        });
  });
}
 
template<typename Fn> inline void IndexMask::foreach_segment(Fn &&fn) const
{
  [[maybe_unused]] int64_t segment_pos = 0;
  for (const int64_t segment_i : IndexRange(segments_num_)) {
    const IndexMaskSegment segment = this->segment(segment_i);
    if constexpr (has_segment_and_start_parameter<Fn>) {
      fn(segment, segment_pos);
      segment_pos += segment.size();
    }
    else {
      fn(segment);
    }
  }
}
 
template<typename Fn>
inline void IndexMask::foreach_segment(const GrainSize grain_size, Fn &&fn) const
{
  threading::parallel_for(this->index_range(), grain_size.value, [&](const IndexRange range) {
    const IndexMask sub_mask = this->slice(range);
    sub_mask.foreach_segment(
        [&fn, range_start = range.start()](const IndexMaskSegment mask_segment,
                                           [[maybe_unused]] const int64_t segment_pos) {
          if constexpr (has_segment_and_start_parameter<Fn>) {
            fn(mask_segment, segment_pos + range_start);
          }
          else {
            fn(mask_segment);
          }
        });
  });
}
 
template<typename Fn> inline void IndexMask::foreach_range(Fn &&fn) const
{
  this->foreach_segment([&](const IndexMaskSegment indices, [[maybe_unused]] int64_t segment_pos) {
    Span<int16_t> base_indices = indices.base_span();
    while (!base_indices.is_empty()) {
      const int64_t next_range_size = unique_sorted_indices::find_size_of_next_range(base_indices);
      const IndexRange range(int64_t(base_indices[0]) + indices.offset(), next_range_size);
      if constexpr (has_segment_and_start_parameter<Fn>) {
        fn(range, segment_pos);
      }
      else {
        fn(range);
      }
      segment_pos += next_range_size;
      base_indices = base_indices.drop_front(next_range_size);
    }
  });
}
 
namespace detail {
IndexMask from_predicate_impl(
    const IndexMask &universe,
    GrainSize grain_size,
    IndexMaskMemory &memory,
    FunctionRef<int64_t(IndexMaskSegment indices, int16_t *r_true_indices)> filter_indices);
}
 
template<typename Fn>
inline IndexMask IndexMask::from_predicate(const IndexMask &universe,
                                           const GrainSize grain_size,
                                           IndexMaskMemory &memory,
                                           Fn &&predicate)
{
  return detail::from_predicate_impl(
      universe,
      grain_size,
      memory,
      [&](const IndexMaskSegment indices, int16_t *__restrict r_true_indices) {
        int16_t *r_current = r_true_indices;
        const int16_t *in_end = indices.base_span().end();
        const int64_t offset = indices.offset();
        for (const int16_t *in_current = indices.base_span().data(); in_current < in_end;
             in_current++) {
          const int16_t local_index = *in_current;
          const int64_t global_index = int64_t(local_index) + offset;
          const bool condition = predicate(global_index);
          *r_current = local_index;
          /* This expects the boolean to be either 0 or 1 which is generally the case but may not
           * be if the values are uninitialized. */
          BLI_assert(ELEM(int8_t(condition), 0, 1));
          /* Branchless conditional increment. */
          r_current += condition;
        }
        const int16_t true_indices_num = int16_t(r_current - r_true_indices);
        return true_indices_num;
      });
}
 
template<typename T, typename Fn>
void IndexMask::from_groups(const IndexMask &universe,
                            IndexMaskMemory &memory,
                            Fn &&get_group_index,
                            MutableSpan<IndexMask> r_masks)
{
  Vector<Vector<T>> indices_by_group(r_masks.size());
  universe.foreach_index([&](const int64_t i) {
    const int group_index = get_group_index(i);
    indices_by_group[group_index].append(T(i));
  });
  for (const int64_t i : r_masks.index_range()) {
    r_masks[i] = IndexMask::from_indices<T>(indices_by_group[i], memory);
  }
}
 
std::optional<IndexRange> inline IndexMask::to_range() const
{
  if (indices_num_ == 0) {
    return IndexRange{};
  }
  const int64_t first_index = this->first();
  const int64_t last_index = this->last();
  if (last_index - first_index == indices_num_ - 1) {
    return IndexRange(first_index, indices_num_);
  }
  return std::nullopt;
}
 
template<int64_t N>
inline Vector<std::variant<IndexRange, IndexMaskSegment>, N> IndexMask::to_spans_and_ranges() const
{
  Vector<std::variant<IndexRange, IndexMaskSegment>, N> segments;
  this->foreach_segment_optimized([&](const auto segment) { segments.append(segment); });
  return segments;
}
 
inline bool operator!=(const IndexMask &a, const IndexMask &b)
{
  return !(a == b);
}
 
}  // namespace blender::index_mask
 
namespace blender {
using index_mask::IndexMask;
using index_mask::IndexMaskFromSegment;
using index_mask::IndexMaskMemory;
using index_mask::IndexMaskSegment;
}  // namespace blender