feat: add AddHash to CardinalityEstimator to allow use of precomputed hashes

feat: add benchmarks for AddHash

Author: onyxmaster

CardinalityEstimation.Benchmark/Program.cs

@@ -4,13 +4,43 @@
 using BenchmarkDotNet.Jobs;
 using BenchmarkDotNet.Running;
 using CardinalityEstimation;
+using System.Text;
 
 var config = DefaultConfig.Instance
                 .AddJob(Job.Default.WithId("Core80").WithRuntime(CoreRuntime.Core80))
                 .AddJob(Job.Default.WithId("Core90").WithRuntime(CoreRuntime.Core90));
 
+BenchmarkRunner.Run<AddHash>(config);
 BenchmarkRunner.Run<DifferentHashes>(config);
 
+[MemoryDiagnoser]
+public class AddHash
+{
+    public static readonly Random Rand = new Random();
+
+    private const int N = 10000000;
+
+    private ulong[] dataHashes = Enumerable.Range(0, N)
+        .Select(_ => Rand.Next().ToString() + Guid.NewGuid().ToString() + Rand.Next().ToString())
+        .Select(x => BitConverter.ToUInt64(System.IO.Hashing.XxHash128.Hash(Encoding.UTF8.GetBytes(x))))
+        .ToArray();
+
+    [Params(4, 16)]
+    public int Bits { get; set; }
+
+    [Benchmark]
+    public void Run() => Run(Bits, (x) => throw new InvalidProgramException());
+
+    private void Run(int bits, GetHashCodeDelegate hashFunction)
+    {
+        var hll = new CardinalityEstimator(hashFunction, bits);
+        for (var i = 0; i < N; i++)
+        {
+            hll.AddHash(dataHashes[i]);
+        }
+    }
+}
+
 [MemoryDiagnoser]
 public class DifferentHashes
 {

CardinalityEstimation/CardinalityEstimator.cs

@@ -469,6 +469,18 @@ public bool Add(ReadOnlyMemory<byte> element)
             return changed;
         }
 
+        /// <summary>
+        /// Adds an element's hash code to the counted set
+        /// </summary>
+        /// <param name="hashCode">Hash code of the element to add</param>
+        /// <returns>True if the estimator's state was modified, false otherwise</returns>
+        public bool AddHash(ulong hashCode)
+        {
+            bool changed = AddElementHash(hashCode);
+            CountAdditions++;
+            return changed;
+        }
+
         /// <summary>
         /// Returns the estimated number of items in the estimator
         /// </summary>