Using & 0x07 (0b111) instead of % 8 so save CPU cycles.
Logical AND uses exactly 1 CPU cycle according to the AVR Instruction Set.
Modulo consists of several commands including division and remainder which takes a lot more cpu cycles
Using <<1 instead of *2 to save cpu cycles
Dont store result in variable because its used only once. no need for memory allocation
maybe this also saves instructions, if the compiler didnt optimize this before. we need to check the assembly here
Merge pull request #2 from schinken/performance-01

Thanks!