stuff

src/game/util/HashMap.h

@@ -0,0 +1,91 @@
+#include "bx/hash.h"
+#include <cassert>
+#include <cstdint>
+
+template <typename T> struct HashMapInsertResult
+{
+    T& Obj = nullptr;
+    bool ElementExists = false;
+};
+
+template <typename T> struct HashMapInsertResultConst
+{
+    const T& Obj = nullptr;
+    bool ElementExists = false;
+};
+
+// BitSize 16 will make the HashTable ~200kb with 65k entries
+template <typename T, uint32_t BitSize> struct HashMapCore
+{
+    static constexpr uint32_t SlotCount = (1 << BitSize);
+    static constexpr uint32_t RequiredDataSize = SlotCount * sizeof(T);
+
+    T* Data = nullptr;
+    uint32_t HashTable[SlotCount]{0};
+
+    // External array that should be RequiredDataSize bytes big
+    void Init(T* data, uint64_t dataSize)
+    {
+        Data = data;
+        assert(data != nullptr);
+        assert(dataSize == RequiredDataSize);
+    }
+
+    bool Has(uint32_t hash) const
+    {
+        return HashTable[FindIdx(hash)] == hash;
+    }
+
+    HashMapInsertResult<T> Get(uint32_t hash)
+    {
+        uint16_t idx = FindIdx(hash);
+        return {Data[idx], HashTable[idx] == hash};
+    }
+
+    const T& Get(uint32_t hash) const
+    {
+        uint16_t idx = FindIdx(hash);
+        return {Data[idx], HashTable[idx] == hash};
+    }
+
+    bool Remove(uint32_t hash); // TODO: requires tombstones so later entries survive
+
+  private:
+    uint16_t FindIdx(uint32_t hash) const
+    {
+        uint32_t mask = SlotCount - 1;
+        uint32_t idx = hash & mask;
+        uint32_t tableEntry = HashTable[idx];
+        uint32_t stepCount = 0;
+        while (tableEntry != hash && tableEntry != 0 && stepCount < UINT16_MAX)
+        {
+            idx = (idx + 1) % SlotCount;
+            tableEntry = HashTable[idx];
+            ++stepCount;
+        }
+        assert(stepCount < UINT16_MAX);
+        return idx;
+    }
+};
+
+namespace HashMapTests
+{
+    struct AAA
+    {
+        int X = 3;
+        int Y = 42;
+    };
+
+    inline void Test()
+    {
+        HashMapCore<AAA, 16> testMap;
+        AAA* backingData = new AAA[testMap.RequiredDataSize]();
+        testMap.Init(backingData, testMap.RequiredDataSize);
+        AAA test{};
+        AAA test2{5, 6};
+        testMap.Get(bx::hash<bx::HashMurmur3>(test)).Obj = test;
+        testMap.Get(bx::hash<bx::HashMurmur3>(test2)).Obj = test2;
+        delete[] backingData;
+    }
+
+} // namespace HashMapTests