Hacker's Delight by Henry S. Warren, Jr.

"Math for Speed Addicts" would serve well as the subtitle for this book. Although die-hard Fourth Generation Language users would call it "Outmoded Bit-wise Operations", it still provides a bunch of math fun to think at that low a level. One of the final chapters especially interested me, because it was a such odds with the rest of the book: Hilbert Curve.