Is the shader code available anywhere? If every particle affects every other, wouldn't 2 million particles require 2,000,000^2 calculations per frame? 30*4 tri

Is the shader code available anywhere? If every particle affects every other, wouldn't 2 million particles require 2,000,000^2 calculations per frame? 30*4 trillion interactions per sec seems a lot... or is there an efficient trick to it (in the shader)?