  Let $G$ be a finite abelian group $G$ with $N$ elements. In this paper we
give a O(N) time algorithm for computing a basis of $G$. Furthermore, we obtain
an algorithm for computing a basis from a generating system of $G$ with $M$
elements having time complexity $O(M\sum_{p|N} e(p)\lceil
p^{1/2}\rceil^{\mu(p)})$, where $p$ runs over all the prime divisors of $N$,
and $p^{e(p)}$, $\mu(p)$ are the exponent and the number of cyclic groups which
are direct factors of the $p$-primary component of $G$, respectively. In case
where $G$ is a cyclic group having a generating system with $M$ elements, a
$O(MN^{\epsilon})$ time algorithm for the computation of a basis of $G$ is
obtained.
