Difference sets of the Hadamard type and quasi-cyclic codes

For every twin prime and prime power p where p ≡ 3(4) we define a (2p + 2, p + 1) binary code by a generator matrix of the form G = [I, Sp, where Sp is given in terms of the incidence matrix of a difference set of the Hadamard type.For p ≡ 3(8) these codes are shown to be self-dual with weights divisible by four.For p = 7, 15, 23, 27, 31 and 35 the codes obtained are probably new and it is not known if they are related to cyclic codes. For p = 7, 15, 19 and 23 we present their weight distributions