This was the clearest explanation of bit masking I have read. I’ve been trying to do some stuff with a micro controller and of course needed to manipulate bits in registers. The bit masking has always been a bit 
confusing. Now it makes perfect sense.
Actually, the reason I’m learning to program for the mac is because I want to write a simple desktop program to talk to my avr controller through the USB port using USART. I’m not sure if this book will help along those lines, but I hope it will give me enough understanding to be able to understand apple’s serialPortExample program which is over my head.