The algorithm above is a 64bit to 32bit reduction method. It performs a 64bit mult and then discards the lower 32bit. I'm not sure if Daniel Lemire invented it as a alternative to modulo, as I've seen the method used before, but he certainly made it popular[1]

There is a 64bit version as well (2x64bit -> 64bit), that when compiled using 128bit multiplication is quite fast too.

The method made it's way into .NET runtime[2]. It is used in HashSet, Dictionary and ConcurrentDictionary today.

[1] https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-...

[2] https://github.com/dotnet/runtime/blob/c22f7f8c73766830b3262...