The legal term you're looking for here is the "Abstraction-Filtration-Comparison" test; What remains if you subtract all the non-copyrightable elements from a given piece of code.
Even in the countries other than USA where algorithms have become patentable, that happened only due to USA blackmailing those countries into changing their laws "to protect (American) IP".
It is true however that there exist some quite old patents which in fact have patented algorithms, but those were disguised as patents for some machines executing those algorithms, in order to satisfy the existing laws.