On extremal double circulant self-dual codes of lengths 90–96

A classification of extremal double circulant self-dual codes of lengths up to 88 is known. We extend this classification to length 96. We give a classification of extremal double circulant self-dual codes of lengths 90, 92, 94 and 96. We also classify double circulant self-dual codes with parameters [90, 45, 14] and [96, 48, 16]. In addition, we demonstrate that no double circulant self-dual [90, 45, 14] code has an extremal self-dual neighbor, and no double circulant self-dual [96, 48, 16] code has a self-dual neighbor with minimum weight at least 18.