is two bits (csr[9:8]) encode the C.NOP instruction; the remaining
the Theory and Application of Cryptology and Information Security, 411–436. Banik, S., Bogdanov, A., Knudsen, L. R., Leander, G., Moradi, A., Peyrin, T., Sasaki, Y., Sasdrich, P., & Sim, S. M. (2016). The SKINNY