Bit Twiddling Hacks (graphics.stanford.edu)

The http://graphics.stanford.edu/~seander/bithacks.html#ZeroInWo... hack is reminiscent of the strlen discussion the other day: http://news.ycombinator.com/item?id=510326

Ah... I have some good memories of adapting some of these for microcontrollers while still in school.

My favorite is Kernighan's method for counting set bits. It's as short and clean as the naive method and not immediately obvious: http://graphics.stanford.edu/~seander/bithacks.html#CountBit...

These are good for showing off to other programmers and ensuring your job security/future contracts at your present place of work.

Also check out Hacker's Delight :

http://www.hackersdelight.org/

http://www.amazon.com/Hackers-Delight-Henry-S-Warren/dp/0201...

If the number of CPU cores increases significantly, with the individual cores getting much simpler, I wonder if bit twiddling will be back.