diff --git a/src/Utils/SparseArray64.cs b/src/Utils/SparseArray64.cs
new file mode 100644
index 0000000..69053a4
--- /dev/null
+++ b/src/Utils/SparseArray64.cs
@@ -0,0 +1,236 @@
+//SparseArray64. Analogous to Dictionary<long, T>, but faster.
+//Benchmark result of indexer.get speed test with 300 elements:
+//[Dictinary: 6.705us] [SparseArray64: 2.512us].
+using System;
+using System.Diagnostics.Contracts;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace DCFApixels.DragonECS.Utils
+{
+    internal class SparseArray64<TValue>
+    {
+        public const int MIN_CAPACITY_BITS_OFFSET = 4;
+        public const int MIN_CAPACITY = 1 << MIN_CAPACITY_BITS_OFFSET;
+        private const int EMPTY = -1;
+
+        private int[] _buckets = Array.Empty<int>();
+        private Entry[] _entries = Array.Empty<Entry>();
+
+        private int _count;
+
+        private int _freeList;
+        private int _freeCount;
+
+        private int _modBitMask;
+
+        #region Properties
+        public TValue this[long keyX, long keyY]
+        {
+            get => _entries[FindEntry(keyX + (keyY << 32))].value;
+            set => Insert(keyX + (keyY << 32), value);
+        }
+        public TValue this[long key]
+        {
+            get => _entries[FindEntry(key)].value;
+            set => Insert(key, value);
+        }
+
+        public int Count => _count;
+        #endregion
+
+        #region Constructors
+        public SparseArray64(int minCapacity = MIN_CAPACITY)
+        {
+            minCapacity = NormalizeCapacity(minCapacity);
+            _buckets = new int[minCapacity];
+            for (int i = 0; i < minCapacity; i++)
+                _buckets[i] = EMPTY;
+            _entries = new Entry[minCapacity];
+            _modBitMask = (minCapacity - 1) & 0x7FFFFFFF;
+        }
+        #endregion
+
+        #region Add
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Add(long keyX, long keyY, TValue value) => Add(keyX + (keyY << 32), value);
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Add(long key, TValue value)
+        {
+#if DEBUG
+            if (Contains(key))
+                throw new ArgumentException("Contains(hashKey) is true");
+#endif
+            Insert(key, value);
+        }
+        #endregion
+
+        #region Find/Insert/Remove
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private int FindEntry(long key)
+        {
+            for (int i = _buckets[unchecked((int)key & _modBitMask)]; i >= 0; i = _entries[i].next)
+                if (_entries[i].hashKey == key) return i;
+            return -1;
+        }
+        private void Insert(long key, TValue value)
+        {
+            int targetBucket = unchecked((int)key & _modBitMask);
+
+            for (int i = _buckets[targetBucket]; i >= 0; i = _entries[i].next)
+            {
+                if (_entries[i].hashKey == key)
+                {
+                    _entries[i].value = value;
+                    return;
+                }
+            }
+
+            int index;
+            if (_freeCount > 0)
+            {
+                index = _freeList;
+                _freeList = _entries[index].next;
+                _freeCount--;
+            }
+            else
+            {
+                if (_count == _entries.Length)
+                {
+                    Resize();
+                    targetBucket = unchecked((int)key & _modBitMask);
+                }
+                index = _count++;
+            }
+
+            _entries[index].next = _buckets[targetBucket];
+            _entries[index].hashKey = key;
+            _entries[index].value = value;
+            _buckets[targetBucket] = index;
+        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool Remove(long keyX, long keyY) => Remove(keyX + (keyY << 32));
+        public bool Remove(long key)
+        {
+            int bucket = unchecked((int)key & _modBitMask);
+            int last = -1;
+            for (int i = _buckets[bucket]; i >= 0; last = i, i = _entries[i].next)
+            {
+                if (_entries[i].hashKey == key)
+                {
+                    if (last < 0)
+                    {
+                        _buckets[bucket] = _entries[i].next;
+                    }
+                    else
+                    {
+                        _entries[last].next = _entries[i].next;
+                    }
+                    _entries[i].next = _freeList;
+                    _entries[i].hashKey = -1;
+                    _entries[i].value = default;
+                    _freeList = i;
+                    _freeCount++;
+                    return true;
+                }
+            }
+            return false;
+        }
+        #endregion
+
+        #region TryGetValue
+        public bool TryGetValue(long key, out TValue value)
+        {
+            int index = FindEntry(key);
+            if (index < 0)
+            {
+                value = default;
+                return false;
+            }
+            value = _entries[index].value;
+            return true;
+        }
+        public bool TryGetValue(long keyX, long keyY, out TValue value)
+        {
+            int index = FindEntry(keyX + (keyY << 32));
+            if (index < 0)
+            {
+                value = default;
+                return false;
+            }
+            value = _entries[index].value;
+            return true;
+        }
+        #endregion
+
+        #region Contains
+        public bool Contains(long keyX, long keyY)
+        {
+            return FindEntry(keyX + (keyY << 32)) >= 0;
+        }
+        public bool Contains(long key)
+        {
+            return FindEntry(key) >= 0;
+        }
+        #endregion
+
+        #region Clear
+        public void Clear()
+        {
+            if (_count > 0)
+            {
+                for (int i = 0; i < _buckets.Length; i++)
+                {
+                    _buckets[i] = -1;
+                }
+                Array.Clear(_entries, 0, _count);
+                _count = 0;
+            }
+        }
+        #endregion
+
+        #region Resize
+        private void Resize()
+        {
+            int newSize = _buckets.Length << 1;
+            _modBitMask = (newSize - 1) & 0x7FFFFFFF;
+
+            Contract.Assert(newSize >= _entries.Length);
+            int[] newBuckets = new int[newSize];
+            for (int i = 0; i < newBuckets.Length; i++)
+                newBuckets[i] = EMPTY;
+
+            Entry[] newEntries = new Entry[newSize];
+            Array.Copy(_entries, 0, newEntries, 0, _count);
+            for (int i = 0; i < _count; i++)
+            {
+                if (newEntries[i].hashKey >= 0)
+                {
+                    int bucket = unchecked((int)newEntries[i].hashKey & _modBitMask);
+                    newEntries[i].next = newBuckets[bucket];
+                    newBuckets[bucket] = i;
+                }
+            }
+            _buckets = newBuckets;
+            _entries = newEntries;
+        }
+
+        private int NormalizeCapacity(int capacity)
+        {
+            int result = MIN_CAPACITY;
+            while (result < capacity) result <<= 1;
+            return result;
+        }
+        #endregion
+
+        #region Utils
+        [StructLayout(LayoutKind.Sequential, Pack = 4)]
+        private struct Entry
+        {
+            public int next;        // Index of next entry, -1 if last
+            public long hashKey;
+            public TValue value;
+        }
+        #endregion
+    }
+}
\ No newline at end of file
diff --git a/src/Utils/SparseArray64.cs.meta b/src/Utils/SparseArray64.cs.meta
new file mode 100644
index 0000000..623cbd0
--- /dev/null
+++ b/src/Utils/SparseArray64.cs.meta
@@ -0,0 +1,11 @@
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