Что вычисляет следующий код?

a = 2187
  v = ->(x){(0..2).to_a.repeated_permutation(x)}
  v[a].map do |r|
    f,l = [-1],0
    (1..2*a).each do |j|
      i = f[j-l-1]
      while i != -1 && r[j%a] != r[(l+i+1)%a]
        l = j-i-1 if r[(l+i+1)%a] > r[j%a]
        i = f[i]
      end
      if i == -1 && r[j%a] != r[(l+i+1)%a]
        l = j if r[(l+i+1)%a] > r[j%a]
        f[j-l] = -1
      else
        f[j-l] = i+1
      end
    end
    r.rotate(l)
  end.uniq.count do |r|
    v[7].count{|s|(0...a).map{|l| r.rotate(l)[0,7]}.include?(s)} == a
  end