Questions regarding stream ciphers in advanced

[Chewhern]

In the advanced of libsodium gitbook website, there's a sub tab of stream ciphers.

I can understand the functionality of xor and xor_ic but in every stream ciphers, there's this function called

int crypto_stream_chacha20(unsigned char *c, unsigned long long clen,
                           const unsigned char *n, const unsigned char *k); 

I couldn't quite get the functionality of this specific method/function. Can someone explain to me, what it does exactly?

[jedisct1]

It serves the same purpose as randombytes_buf_deterministic(): given a seed, it fills the output buffer with a deterministic sequence, that looks like random.

Unless you specifically need this function, you should just use randombytes_buf_deterministic() instead, if only because the name is self-explanatory.