Bit Twiddling Hacks (2005) (graphics.stanford.edu)

This has been popular over the years, but hasn't had attention on HN in a while:

https://hn.algolia.com/?q=bit+twiddling+hacks#!/story/foreve...

We put 2005 on it, though the Internet Archive says there were earlier versions.

He should pay bounties in BTC...

There's also a lot of 64-bit hacks on pages related to chess programming (8x8 boards). For example: https://chessprogramming.wikispaces.com/Bitboards

And my faviourite bit hack question on SO: https://stackoverflow.com/questions/14537831/isolate-specifi...

Neat. Also here's some other sources beyond the usual CS bookshelf suspects:

http://www.hackersdelight.org/

http://www.inwap.com/pdp10/hbaker/hakmem/hakmem.html

(We recently had to grab the C standards in order to bust out some integer under/overflow macros that wouldn't be brittle.)

Another resource in the same vein (it links to this page, among others):

http://aggregate.org/MAGIC/

It's an awesome page.

I would guess one of the reasons it's here though is that it's almost required reading for Google interviews, #DetermineIfPowerOf2 is a particular favorite.