Replace modulo with fastmodulo in HashSet and Hashtable

[danmoseley]

The performance optimization by @benaadams in Dictionary<K,V> in dotnet/coreclr#27299 should be applied to

• Hashset<T>
• Hashtable

[GrabYourPitchforks]

HashSet<T> should also get the non-randomized string hash code optimization that Dictionary<TKey, TValue> enjoys. That optimization should pay healthy dividends.

[eanova]

I took a peek at this last night. Few test errors but I think I can resolve those and push a PR by tomorrow for HashSet.

[danmoseley]

Sounds good. It would be good to share perf numbers before/after in your PR: https://github.com/dotnet/performance/blob/master/docs/benchmarking-workflow-dotnet-runtime.md

[danmoseley]

That doc just got updated for 50 and this new repo, so if you see any glitch in it, let us know!

[eanova]

I'll post back here if I get stuck on the performance tests.

[danmoseley]

OK! @adamsitnik owns that excellent doc.