>why not "right rotate 2 XOR right rotate 3 XOR right shift 4" In this case, you generally want shifts that are far apart so bits that far apart have a chance

>why not "right rotate 2 XOR right rotate 3 XOR right shift 4" In this case, you generally want shifts that are far apart so bits that far apart have a chance to influence each other. The other operations have only local effects on bits (and, or, xor affect only the same bit position; add affects the same bit position and perhaps a few that follow via carries). Only the shifts/rotates give a chance for "non-local" effects.