It doesn't seem that this affects wall time for a single addition though, at least on typical x86 CPUs. If you look at Agner's performance tables [1], ADD instr

It doesn't seem that this affects wall time for a single addition though, at least on typical x86 CPUs. If you look at Agner's performance tables [1], ADD instructions always take the same number of cycles. I'm not a hardware expert, but I'm guessing that what's happening here is that transistors get hotter with certain input values more than others. Eventually this results in higher overall CPU temperature and a lowering of CPU frequency to compensate. [1] https://www.agner.org/optimize/instruction_tables.pdf https://www.agner.org/optimize/instruction_tables.pdf