You're right, that's a pretty careless mistake. Considering that, the only way to stretch this into locality would be to assume that sum would be used in rapid

You're right, that's a pretty careless mistake. Considering that, the only way to stretch this into locality would be to assume that sum would be used in rapid enough succession so as to be able to live in a register instead of go back to a cache or even memory. That difference seems negligible, though.