[Union] Add case in benckmark.

Author: reegeek

Documents/BenchmarksResults/Union.md

@@ -7,16 +7,17 @@
 ``` ini
 
 BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
-Intel Core i7-8750H CPU 2.20GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
-.NET Core SDK=5.0.101
-  [Host]     : .NET Core 5.0.1 (CoreCLR 5.0.120.57516, CoreFX 5.0.120.57516), X64 RyuJIT
-  DefaultJob : .NET Core 5.0.1 (CoreCLR 5.0.120.57516, CoreFX 5.0.120.57516), X64 RyuJIT
+Intel Core i7-7700 CPU 3.60GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
+.NET Core SDK=5.0.202
+  [Host]     : .NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT
+  DefaultJob : .NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT
 
 
 ```
-|                         Method |     Mean |   Error |  StdDev | Ratio |   Gen 0 |   Gen 1 |   Gen 2 | Allocated |
-|------------------------------- |---------:|--------:|--------:|------:|--------:|--------:|--------:|----------:|
-|                           Linq | 347.2 μs | 2.02 μs | 1.88 μs |  1.00 | 90.8203 | 90.8203 | 90.8203 |  524824 B |
-|                     StructLinq | 155.0 μs | 0.73 μs | 0.68 μs |  0.45 |       - |       - |       - |      64 B |
-|            StructLinqZeroAlloc | 155.6 μs | 0.47 μs | 0.41 μs |  0.45 |       - |       - |       - |         - |
-| StructLinqZeroAllocAndComparer | 121.2 μs | 0.43 μs | 0.40 μs |  0.35 |       - |       - |       - |         - |
+|                            Method |     Mean |   Error |  StdDev | Ratio |   Gen 0 |   Gen 1 |   Gen 2 | Allocated |
+|---------------------------------- |---------:|--------:|--------:|------:|--------:|--------:|--------:|----------:|
+|                              Linq | 424.0 μs | 8.27 μs | 7.74 μs |  1.00 | 90.8203 | 90.8203 | 90.8203 |  524824 B |
+|                        StructLinq | 184.9 μs | 2.72 μs | 2.42 μs |  0.44 |       - |       - |       - |      64 B |
+|               StructLinqZeroAlloc | 184.4 μs | 1.89 μs | 1.58 μs |  0.43 |       - |       - |       - |         - |
+|    StructLinqZeroAllocAndComparer | 149.1 μs | 0.82 μs | 0.69 μs |  0.35 |       - |       - |       - |         - |
+| StructLinqZeroAllocAndComparerSum | 132.7 μs | 0.41 μs | 0.37 μs |  0.31 |       - |       - |       - |         - |

src/StructLinq.Benchmark/Union.cs

@@ -63,5 +63,14 @@ public int StructLinqZeroAllocAndComparer()
             return sum;
         }
 
+        [Benchmark]
+        public int StructLinqZeroAllocAndComparerSum()
+        {
+            var comparer = new DefaultStructEqualityComparer();
+            return array1.ToStructEnumerable()
+                         .Union(array2.ToStructEnumerable(), comparer, x=> x, x=>x)
+                         .Sum(x=>x);
+        }
+
     }
 }