code: def scalarmult_B(e):
      
      # scalarmult(B, l) is the identity
      e = e % l
      P = ident
      for i in range(253):
          if e & 1:
              P = edwards_add(P, Bpow[i])
          e = e // 2
      assert e == 0, e
      return P
docs: Implements scalarmult(B, e) more efficiently.