# In the shor's quantum circuit, what is the transformation of the modular operating gates?

I know different parts of this circuit, just I have a problem with that part that I circled in picture. I want to know the function of that part. If you have useful information about it, please share it with me. Thank you so much.

It's a modular multiplication gate. It permutes the states such that, for all $$k$$ below $$N$$, state $$|k\rangle$$ becomes state $$|k \cdot c \pmod{N}\rangle$$ where $$N$$ is the number being factored and $$c = b^{2^{2n-1}} \pmod{N}$$ is a classically computed constant and $$b$$ is the base value chosen randomly at the start of the algorithm.