BLI: new C++ hash table data structures

This commit adds some new hashing based data structures to blenlib.
All of them use open addressing with probing currently.
Furthermore, they support small object optimization, but it is not
customizable yet. I'll add support for this when necessary.
The following main data structures are included:

**Set**
A collection of values, where every value must exist at most once.
This is similar to a Python `set`.

**SetVector**
A combination of a Set and a Vector. It supports fast search for
elements and maintains insertion order when there are no deletes.
All elements are stored in a continuous array. So they can be
iterated over using a normal `ArrayRef`.

**Map**
A set of key-value-pairs, where every key must exist at most once.
This is similar to a Python `dict`.

**StringMap**
A special map for the case when the keys are strings. This case is
fairly common and allows for some optimizations. Most importantly,
many unnecessary allocations can be avoided by storing strings in
a single buffer. Furthermore, the interface of this class uses
`StringRef` to avoid unnecessary conversions.

This commit is a continuation of rB369d5e8ad2bb7.

1 files changed, 470 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_set.h b/source/blender/blenlib/BLI_set.h
new file mode 100644
index 00000000000..33b02badf48
--- /dev/null
+++ b/source/blender/blenlib/BLI_set.h
@@ -0,0 +1,470 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup bli
+ *
+ * This file provides a set implementation that uses open addressing with probing.
+ */
+
+#pragma once
+
+#include "BLI_hash_cxx.h"
+#include "BLI_open_addressing.h"
+#include "BLI_vector.h"
+
+namespace BLI {
+
+// clang-format off
+
+#define ITER_SLOTS_BEGIN(VALUE, ARRAY, OPTIONAL_CONST, R_ITEM, R_OFFSET) \
+  uint32_t hash = DefaultHash<T>{}(VALUE); \
+  uint32_t perturb = hash; \
+  while (true) { \
+    uint32_t item_index = (hash & ARRAY.slot_mask()) >> OFFSET_SHIFT; \
+    uint8_t R_OFFSET = hash & OFFSET_MASK; \
+    uint8_t initial_offset = R_OFFSET; \
+    OPTIONAL_CONST Item &R_ITEM = ARRAY.item(item_index); \
+    do {
+
+#define ITER_SLOTS_END(R_OFFSET) \
+      R_OFFSET = (R_OFFSET + 1) & OFFSET_MASK; \
+    } while (R_OFFSET != initial_offset); \
+    perturb >>= 5; \
+    hash = hash * 5 + 1 + perturb; \
+  } ((void)0)
+
+// clang-format on
+
+template<typename T, typename Allocator = GuardedAllocator> class Set {
+ private:
+  static constexpr uint OFFSET_MASK = 3;
+  static constexpr uint OFFSET_SHIFT = 2;
+
+  class Item {
+   private:
+    static constexpr uint8_t IS_EMPTY = 0;
+    static constexpr uint8_t IS_SET = 1;
+    static constexpr uint8_t IS_DUMMY = 2;
+
+    uint8_t m_status[4];
+    char m_values[4 * sizeof(T)];
+
+   public:
+    static constexpr uint slots_per_item = 4;
+
+    Item()
+    {
+      for (uint offset = 0; offset < 4; offset++) {
+        m_status[offset] = IS_EMPTY;
+      }
+    }
+
+    ~Item()
+    {
+      for (uint offset = 0; offset < 4; offset++) {
+        if (m_status[offset] == IS_SET) {
+          destruct(this->value(offset));
+        }
+      }
+    }
+
+    Item(const Item &other)
+    {
+      for (uint offset = 0; offset < 4; offset++) {
+        uint8_t status = other.m_status[offset];
+        m_status[offset] = status;
+        if (status == IS_SET) {
+          T *src = other.value(offset);
+          T *dst = this->value(offset);
+          new (dst) T(*src);
+        }
+      }
+    }
+
+    Item(Item &&other) noexcept
+    {
+      for (uint offset = 0; offset < 4; offset++) {
+        uint8_t status = other.m_status[offset];
+        m_status[offset] = status;
+        if (status == IS_SET) {
+          T *src = other.value(offset);
+          T *dst = this->value(offset);
+          new (dst) T(std::move(*src));
+        }
+      }
+    }
+
+    Item &operator=(const Item &other) = delete;
+    Item &operator=(Item &&other) = delete;
+
+    T *value(uint offset) const
+    {
+      return (T *)(m_values + offset * sizeof(T));
+    }
+
+    void copy_in(uint offset, const T &value)
+    {
+      BLI_assert(m_status[offset] != IS_SET);
+      m_status[offset] = IS_SET;
+      T *dst = this->value(offset);
+      new (dst) T(value);
+    }
+
+    void move_in(uint offset, T &value)
+    {
+      BLI_assert(m_status[offset] != IS_SET);
+      m_status[offset] = IS_SET;
+      T *dst = this->value(offset);
+      new (dst) T(std::move(value));
+    }
+
+    void set_dummy(uint offset)
+    {
+      BLI_assert(m_status[offset] == IS_SET);
+      m_status[offset] = IS_DUMMY;
+      destruct(this->value(offset));
+    }
+
+    bool is_empty(uint offset) const
+    {
+      return m_status[offset] == IS_EMPTY;
+    }
+
+    bool is_set(uint offset) const
+    {
+      return m_status[offset] == IS_SET;
+    }
+
+    bool is_dummy(uint offset) const
+    {
+      return m_status[offset] == IS_DUMMY;
+    }
+
+    bool has_value(uint offset, const T &value) const
+    {
+      return m_status[offset] == IS_SET && *this->value(offset) == value;
+    }
+  };
+
+  using ArrayType = OpenAddressingArray<Item, 1, Allocator>;
+  ArrayType m_array = OpenAddressingArray<Item>();
+
+ public:
+  Set() = default;
+
+  /**
+   * Create a new set that contains the given elements.
+   */
+  Set(ArrayRef<T> values)
+  {
+    this->reserve(values.size());
+    for (const T &value : values) {
+      this->add(value);
+    }
+  }
+
+  /**
+   * Create a new set from an initializer list.
+   */
+  Set(std::initializer_list<T> values) : Set(ArrayRef<T>(values))
+  {
+  }
+
+  /**
+   * Make the set large enough to hold the given amount of elements.
+   */
+  void reserve(uint32_t min_usable_slots)
+  {
+    if (m_array.slots_usable() < min_usable_slots) {
+      this->grow(min_usable_slots);
+    }
+  }
+
+  /**
+   * Add a new element to the set.
+   * Asserts that the element did not exist in the set before.
+   */
+  void add_new(const T &value)
+  {
+    BLI_assert(!this->contains(value));
+    this->ensure_can_add();
+
+    ITER_SLOTS_BEGIN (value, m_array, , item, offset) {
+      if (item.is_empty(offset)) {
+        item.copy_in(offset, value);
+        m_array.update__empty_to_set();
+        return;
+      }
+    }
+    ITER_SLOTS_END(offset);
+  }
+
+  /**
+   * Add a new value to the set if it does not exist yet.
+   */
+  bool add(const T &value)
+  {
+    this->ensure_can_add();
+
+    ITER_SLOTS_BEGIN (value, m_array, , item, offset) {
+      if (item.is_empty(offset)) {
+        item.copy_in(offset, value);
+        m_array.update__empty_to_set();
+        return true;
+      }
+      else if (item.has_value(offset, value)) {
+        return false;
+      }
+    }
+    ITER_SLOTS_END(offset);
+  }
+
+  /**
+   * Add multiple elements to the set.
+   */
+  void add_multiple(ArrayRef<T> values)
+  {
+    for (const T &value : values) {
+      this->add(value);
+    }
+  }
+
+  /**
+   * Add multiple new elements to the set.
+   * Asserts that none of the elements existed in the set before.
+   */
+  void add_multiple_new(ArrayRef<T> values)
+  {
+    for (const T &value : values) {
+      this->add_new(value);
+    }
+  }
+
+  /**
+   * Returns true when the value is in the set, otherwise false.
+   */
+  bool contains(const T &value) const
+  {
+    ITER_SLOTS_BEGIN (value, m_array, const, item, offset) {
+      if (item.is_empty(offset)) {
+        return false;
+      }
+      else if (item.has_value(offset, value)) {
+        return true;
+      }
+    }
+    ITER_SLOTS_END(offset);
+  }
+
+  /**
+   * Remove the value from the set.
+   * Asserts that the value exists in the set currently.
+   */
+  void remove(const T &value)
+  {
+    BLI_assert(this->contains(value));
+    ITER_SLOTS_BEGIN (value, m_array, , item, offset) {
+      if (item.has_value(offset, value)) {
+        item.set_dummy(offset);
+        m_array.update__set_to_dummy();
+        return;
+      }
+    }
+    ITER_SLOTS_END(offset);
+  }
+
+  Vector<T> to_small_vector() const
+  {
+    Vector<T> vector;
+    vector.reserve(this->size());
+    for (const T &value : *this) {
+      vector.append(value);
+    }
+    return vector;
+  }
+
+  uint32_t size() const
+  {
+    return m_array.slots_set();
+  }
+
+  /**
+   * Returns true when there is at least one element that is in both sets.
+   * Otherwise false.
+   */
+  static bool Intersects(const Set &a, const Set &b)
+  {
+    /* Make sure we iterate over the shorter set. */
+    if (a.size() > b.size()) {
+      return Intersects(b, a);
+    }
+
+    for (const T &value : a) {
+      if (b.contains(value)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Returns true when there is no value that is in both sets.
+   * Otherwise false.
+   */
+  static bool Disjoint(const Set &a, const Set &b)
+  {
+    return !Intersects(a, b);
+  }
+
+  void print_table() const
+  {
+    std::cout << "Hash Table:\n";
+    std::cout << "  Size: " << m_array.slots_set() << '\n';
+    std::cout << "  Capacity: " << m_array.slots_total() << '\n';
+    uint32_t item_index = 0;
+    for (const Item &item : m_array) {
+      std::cout << "   Item: " << item_index++ << '\n';
+      for (uint offset = 0; offset < 4; offset++) {
+        std::cout << "    " << offset << " \t";
+        if (item.is_empty(offset)) {
+          std::cout << "    <empty>\n";
+        }
+        else if (item.is_set(offset)) {
+          const T &value = *item.value(offset);
+          uint32_t collisions = this->count_collisions(value);
+          std::cout << "    " << value << "  \t Collisions: " << collisions << '\n';
+        }
+        else if (item.is_dummy(offset)) {
+          std::cout << "    <dummy>\n";
+        }
+      }
+    }
+  }
+
+  class Iterator {
+   private:
+    const Set *m_set;
+    uint32_t m_slot;
+
+   public:
+    Iterator(const Set *set, uint32_t slot) : m_set(set), m_slot(slot)
+    {
+    }
+
+    Iterator &operator++()
+    {
+      m_slot = m_set->next_slot(m_slot + 1);
+      return *this;
+    }
+
+    const T &operator*() const
+    {
+      uint32_t item_index = m_slot >> OFFSET_SHIFT;
+      uint offset = m_slot & OFFSET_MASK;
+      const Item &item = m_set->m_array.item(item_index);
+      BLI_assert(item.is_set(offset));
+      return *item.value(offset);
+    }
+
+    friend bool operator==(const Iterator &a, const Iterator &b)
+    {
+      BLI_assert(a.m_set == b.m_set);
+      return a.m_slot == b.m_slot;
+    }
+
+    friend bool operator!=(const Iterator &a, const Iterator &b)
+    {
+      return !(a == b);
+    }
+  };
+
+  friend Iterator;
+
+  Iterator begin() const
+  {
+    return Iterator(this, this->next_slot(0));
+  }
+
+  Iterator end() const
+  {
+    return Iterator(this, m_array.slots_total());
+  }
+
+ private:
+  uint32_t next_slot(uint32_t slot) const
+  {
+    for (; slot < m_array.slots_total(); slot++) {
+      uint32_t item_index = slot >> OFFSET_SHIFT;
+      uint offset = slot & OFFSET_MASK;
+      const Item &item = m_array.item(item_index);
+      if (item.is_set(offset)) {
+        return slot;
+      }
+    }
+    return slot;
+  }
+
+  void ensure_can_add()
+  {
+    if (UNLIKELY(m_array.should_grow())) {
+      this->grow(this->size() + 1);
+    }
+  }
+
+  BLI_NOINLINE void grow(uint32_t min_usable_slots)
+  {
+    ArrayType new_array = m_array.init_reserved(min_usable_slots);
+
+    for (Item &old_item : m_array) {
+      for (uint8_t offset = 0; offset < 4; offset++) {
+        if (old_item.is_set(offset)) {
+          this->add_after_grow(*old_item.value(offset), new_array);
+        }
+      }
+    }
+
+    m_array = std::move(new_array);
+  }
+
+  void add_after_grow(T &old_value, ArrayType &new_array)
+  {
+    ITER_SLOTS_BEGIN (old_value, new_array, , item, offset) {
+      if (item.is_empty(offset)) {
+        item.move_in(offset, old_value);
+        return;
+      }
+    }
+    ITER_SLOTS_END(offset);
+  }
+
+  uint32_t count_collisions(const T &value) const
+  {
+    uint32_t collisions = 0;
+    ITER_SLOTS_BEGIN (value, m_array, const, item, offset) {
+      if (item.is_empty(offset) || item.has_value(offset, value)) {
+        return collisions;
+      }
+      collisions++;
+    }
+    ITER_SLOTS_END(offset);
+  }
+};
+
+#undef ITER_SLOTS_BEGIN
+#undef ITER_SLOTS_END
+
+}  // namespace BLI