18. The apparatus according to claim 16 , wherein said distance between said reference vector and said at least sorted representation of said input vector corresponds to a distance between a previously checked candidate vector of said plurality of candidate vectors and said at least sorted representation of said input vector computed for said previously checked candidate vector, and is retrieved from a memory where it has been at least temporarily stored.
16. The apparatus according to claim 12 , further caused to, in case said check for said candidate vector yields a negative result, check if said computed distance between said at least sorted representation of said input vector and said candidate vector is smaller than said distance between said reference vector and said at least sorted representation of said input vector, and to define said reference vector to be said candidate vector if said computed distance between said at least sorted representation of said input vector and said candidate vector is smaller than said distance between said reference vector and said at least sorted representation of said input vector.