From 85f86c6511f0249546567bf6c00f57357be97421 Mon Sep 17 00:00:00 2001
From: Aristarkh Zagorodnikov <xm@x-infinity.com>
Date: Sun, 21 Sep 2025 21:25:39 +0100
Subject: [PATCH] perf: minor improvements for AddHashElement (elide extra
 bounds check, remove the need for IDictionary devirtualization, reduce
 branching graph depth), this adds about 13% on .NET 8

---
 CardinalityEstimation/CardinalityEstimator.cs | 21 ++++++++++++-------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/CardinalityEstimation/CardinalityEstimator.cs b/CardinalityEstimation/CardinalityEstimator.cs
index ae526c1..a4005c1 100644
--- a/CardinalityEstimation/CardinalityEstimator.cs
+++ b/CardinalityEstimation/CardinalityEstimator.cs
@@ -111,7 +111,7 @@ public class CardinalityEstimator : ICardinalityEstimator<string>, ICardinalityE
         /// <summary>
         /// Lookup dictionary for the sparse representation of HLL buckets
         /// </summary>
-        private IDictionary<ushort, byte> lookupSparse;
+        private Dictionary<ushort, byte> lookupSparse;
 
         /// <summary>
         /// Max number of elements to hold in the sparse representation before switching to dense
@@ -787,19 +787,24 @@ private bool AddElementHash(ulong hashCode)
             if (isSparse)
             {
                 lookupSparse.TryGetValue(substream, out byte prevRank);
-                lookupSparse[substream] = Math.Max(prevRank, sigma);
-                changed = changed || (prevRank != sigma && lookupSparse[substream] == sigma);
-                if (lookupSparse.Count > sparseMaxElements)
+                if (sigma > prevRank)
                 {
-                    SwitchToDenseRepresentation();
+                    lookupSparse[substream] = sigma;
+                    if (lookupSparse.Count > sparseMaxElements)
+                    {
+                        SwitchToDenseRepresentation();
+                    }
                     changed = true;
                 }
             }
             else
             {
-                var prevMax = lookupDense[substream];
-                lookupDense[substream] = Math.Max(prevMax, sigma);
-                changed = changed || (prevMax != sigma && lookupDense[substream] == sigma);
+                ref var value = ref lookupDense[substream];
+                if (sigma > value)
+                {
+                    value = sigma;
+                    changed = true;
+                }
             }
             return changed;
         }