Weight distributions of cyclic self-dual codes

We give a 1-level squaring construction for binary repeated-root cyclic codes of length n=2/sup a/b, a(alpha)1, b odd. This allows us to obtain the weight distributions of all cyclic binary self-dual codes of lengths up to 110, which are not accessible by direct computation. We also use the shadow construction, as a particular method for Type I self-dual codes.