MIT HAKMEM from 1972 contains lots of weird little hacks and tricks and is quite an entertaining read, because you can see followup responses of people figuring out better ways or the math behind it. For example, check out Item 149, then the next few.
Won sent me some more cool similar stuff :
The Aggregate "Magic" algorithms; this stuff is mostly pretty weak, but something might be useful there. Not related to Eberly's Magic Software which is more better.
Doing divide with multiply detailed page on how to do it correctly. This is something I hack frequently and get slightly wrong.