Faster than HashSet

I have an interesting challenge where HashSet operations are the bottleneck for my simulation. I decided to see if I could go faster using an int64 array as the backing store and bit operations for updating. It appears that you can if you can make assumptions about your domain.

Results

// * Summary *

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
AMD Ryzen 9 3900X, 1 CPU, 24 logical and 12 physical cores
.NET SDK=6.0.101
  [Host]     : .NET 6.0.2 (6.0.222.6406), X64 RyuJIT DEBUG
  DefaultJob : .NET 6.0.2 (6.0.222.6406), X64 RyuJIT

Method	Mean	Error	StdDev	Gen 0	Gen 1	Allocated
HashSetAdd	121.78 ns	1.309 ns	1.224 ns	-	-	-
HashSetRemove	118.60 ns	0.697 ns	0.618 ns	-	-	-
HashSetMap	79,729.70 ns	374.712 ns	350.506 ns	5.7373	0.4883	49,016 B
BitSetAdd	66.24 ns	0.180 ns	0.160 ns	-	-	-
BitSetRemove	67.86 ns	0.212 ns	0.177 ns	-	-	-
BitSetMap	29,746.68 ns	588.177 ns	1,045.484 ns	5.8289	0.5798	48,976 B
InliningBitSetAdd	49.70 ns	1.001 ns	1.436 ns	-	-	-
InliningBitSetRemove	50.01 ns	1.027 ns	1.716 ns	-	-	-