BinarySearch()

procedure BINSRCH(F,n,i,K)
// Search an ordered sequential file F with records R1, ...,Rn and
   the keys K1  K2  ...  Kn for a record Ri such that Ki = K;
   i = 0 if there is no such record else Ki = K. Throughout the
   algorithm, l is the smallest index such that Kl may be K and u
   the largest index such that Ku may be K//

    l  1; u  n
    while l  u do
    m  (l+ u)/2      //compute index of middle record//
    case
        :K > Km: l  m + 1       //look in upper half//
        :K = Km: i  m; return
        :K < Km: u  m - 1       //look in lower half//
    end
  end
  i  0    //no record with key K//
end BINSRCH