Implement Murmur2 hashing algorithm

src/contrib/cluster/Akka.Cluster.Sharding/Internal/Murmur2.cs

@@ -0,0 +1,62 @@
+using System;
+using System.Text;
+
+namespace Akka.Cluster.Sharding.Internal
+{
+    public static class Murmur2
+    {
+        public static int ToPositive(this int value)
+            => value & 0x7fffffff;
+
+        public static int GetHash(this byte[] data)
+        {
+            const uint seed = 0x9747b28c;
+            // 'm' and 'r' are mixing constants generated offline.
+            // They're not really 'magic', they just happen to work well.
+            const uint m = 0x5bd1e995;
+            const int r = 24;
+
+            var length = (uint)data.Length;
+
+            // Initialize the hash to a random value
+            var h = seed ^ length;
+            for (var i = 0; i < length; i += 4)
+            {
+                var k = BitConverter.ToUInt32(data, i);
+                k *= m;
+                k ^= k >> r;
+                k *= m;
+                h *= m;
+                h ^= k;
+            }
+            // Handle the last few bytes of the input array
+            switch (length % 4)
+            {
+                case 3:
+                    h ^= (uint)data[(length & ~3) + 2] << 16;
+                    h ^= (uint)data[(length & ~3) + 1] << 8;
+                    h ^= data[length & ~3];
+                    h *= m;
+                    break;
+                case 2:
+                    h ^= (uint)data[(length & ~3) + 1] << 8;
+                    h ^= data[length & ~3];
+                    h *= m;
+                    break;
+                case 1:
+                    h ^= data[length & ~3];
+                    h *= m;
+                    break;
+            }
+
+            h ^= h >> 13;
+            h *= m;
+            h ^= h >> 15;
+            return (int)h;
+        }
+
+        // To match https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/producer/internals/DefaultPartitioner.java#L59
+        public static string ShardId(string entityId, int nrShards)
+            => (GetHash(Encoding.UTF8.GetBytes(entityId)).ToPositive() % nrShards).ToString();
+    }
+}