What is the runtime complexity of the `BLAKE2` hash function?
Blake2 takes (in either variant) the input, processes it in fixed-size blocks, padding the last block with zeroes to the full block size if required. The processing operation happens in constant time (it takes a constant number of cycles, big-O notation is meaningless since the input size is fixed). The initialization and finalization steps also take constant time. Therefore, the overall operation takes $O(n)$ time.