Bit Twiddling Hacks

This kind of hacks is a major part of how we made Scala.js' 64-bit integers fast (the fastest known implementation of 64-bit integers on JavaScript). See [1] for the implementation, and [2] at section 4.4 for the long explanation with benchmarks and the other tricks we use. [1] https://github.com/scala-js/scala-js/blob/v1.3.1/linker-priv... [2] https://lampwww.epfl.ch/~doeraene/thesis/doeraene-thesis-201...

My favourite bit of bit twiddling doesn't seem to appear here - how to enumerate all the subsets of bits set. Like so many bit-twiddling hacks, I first saw this in chess engines: https://www.chessprogramming.org/Traversing_Subsets_of_a_Set

Just a fair warning as someone who has made extensive use of this page in the past: many of these hacks often end up slower these days on modern CPUs than naive approaches. Especially the no-branch and no-multiply math ops. As always, be sure to performance test your code if you're getting into obfuscating your algorithms to boost speeds. That said, there are still plenty of real gems in there. And on that note, here's one of my favorite bit-twiddling…

It's worth noting that modern x86 CPUs have specialized extensions for bit manipulation. Furthermore C23 added stdbit.h that has some operations for bit manipulation https://en.wikipedia.org/wiki/X86_Bit_manipulation_instructi... https://thephd.dev/_vendor/future_cxx/papers/C%20-%20Modern%...