I am currently trying to dissect the low level cryptography protocols of the lightning network and I realize that in many places chacha20 is being used. I tried reading about it in the Wikipedia Article there it says:
This gives Salsa20 and ChaCha the unusual advantage that the user can efficiently seek to any position in the key stream in constant time. Salsa20 offers speeds of around 4–14 cycles per byte in software on modern x86 processors, and reasonable hardware performance. It is not patented, and Bernstein has written several public domain implementations optimized for common architectures.
While I see the later parts about not being patented and optimzed for many architectures is nice I don't get the first sentence of the Quote. What does it mean that one can efficiently seek to any position in the key stream in constant time?