On self-dual double circulant codes
  Self-dual double circulant codes of odd dimension are shown to be dihedral in even characteristic and consta-dihedral in odd characteristic. Exact counting formulae are derived for them and used to show they contain families of codes with relative distance satisfying a modified Gilbert-Varshamov bound. 
Adel Alahmadi, Funda \"Ozdemir, Patrick Sol\'e
cs.IT math.IT