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, 100 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_hash_cxx.h b/source/blender/blenlib/BLI_hash_cxx.h
new file mode 100644
index 00000000000..b9a53f29a04
--- /dev/null
+++ b/source/blender/blenlib/BLI_hash_cxx.h
@@ -0,0 +1,100 @@
+/*
+ * 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 default hash functions for some primitive types. The hash functions can be
+ * used by containers such as Map and Set.
+ */
+
+#pragma once
+
+#include <functional>
+#include <string>
+#include <utility>
+
+#include "BLI_utildefines.h"
+#include "BLI_math_base.h"
+
+namespace BLI {
+
+template<typename T> struct DefaultHash {
+};
+
+#define TRIVIAL_DEFAULT_INT_HASH(TYPE) \
+  template<> struct DefaultHash<TYPE> { \
+    uint32_t operator()(TYPE value) const \
+    { \
+      return (uint32_t)value; \
+    } \
+  }
+
+/**
+ * Cannot make any assumptions about the distribution of keys, so use a trivial hash function by
+ * default. The hash table implementations are designed to take all bits of the hash into account
+ * to avoid really bad behavior when the lower bits are all zero. Special hash functions can be
+ * implemented when more knowledge about a specific key distribution is available.
+ */
+TRIVIAL_DEFAULT_INT_HASH(int8_t);
+TRIVIAL_DEFAULT_INT_HASH(uint8_t);
+TRIVIAL_DEFAULT_INT_HASH(int16_t);
+TRIVIAL_DEFAULT_INT_HASH(uint16_t);
+TRIVIAL_DEFAULT_INT_HASH(int32_t);
+TRIVIAL_DEFAULT_INT_HASH(uint32_t);
+TRIVIAL_DEFAULT_INT_HASH(int64_t);
+
+template<> struct DefaultHash<float> {
+  uint32_t operator()(float value) const
+  {
+    return *(uint32_t *)&value;
+  }
+};
+
+template<> struct DefaultHash<std::string> {
+  uint32_t operator()(const std::string &value) const
+  {
+    uint32_t hash = 5381;
+    for (char c : value) {
+      hash = hash * 33 + c;
+    }
+    return hash;
+  }
+};
+
+/**
+ * While we cannot guarantee that the lower 3 bits or a pointer are zero, it is safe to assume
+ * this in the general case. MEM_malloc only returns 8 byte aligned addresses on 64-bit systems.
+ */
+template<typename T> struct DefaultHash<T *> {
+  uint32_t operator()(const T *value) const
+  {
+    uintptr_t ptr = POINTER_AS_UINT(value);
+    uint32_t hash = (uint32_t)(ptr >> 3);
+    return hash;
+  }
+};
+
+template<typename T1, typename T2> struct DefaultHash<std::pair<T1, T2>> {
+  uint32_t operator()(const std::pair<T1, T2> &value) const
+  {
+    uint32_t hash1 = DefaultHash<T1>{}(value.first);
+    uint32_t hash2 = DefaultHash<T2>{}(value.second);
+    return hash1 ^ (hash2 * 33);
+  }
+};
+
+}  // namespace BLI