With your modified code I am now seeing #1 run about 3x faster than #2. I also still strongly suspect you weren't measuring anything at all before your modifica

With your modified code I am now seeing #1 run about 3x faster than #2. I also still strongly suspect you weren't measuring anything at all before your modifications. Benchmarking is tricky and its hard to say if you are really measuring what you think you are. This is especially true with UB in your loop. It would be best to separate the program into 3 and then investigate the assembly.