I'm trying to get understanding of Salsa20 algorithm. There is an official specification from Daniel J. Bernstein at link. Everything in spec is clear and I could write an implementation on Swift.
But I met Salsa20 cipher algorithm implemented by other developers Crypto and TLS for C++11 , Salsa20 written on Python The developers perform some operations with words at positions 8 and 9 after generating ciphertext message:
I didn't saw these operations in the original Salsa20 spec. What do these increments mean?