irred : [8]
irred = 0x1b
xtimes a = (if a ! (length a - 1) then a' ^ irred else a')
  where a' = a << 1

gtimes : ([8], [8]) -> [8]
gtimes (a, b)
  = (if b == 0 then 0 else xtimes (gtimes (a, b >> 1)) ^ a')
    // endianness difference from Cryptol-1 test:
  where a' = if b ! 0 then a else 0

check22 = [ gtimes (13, x) | x <- [ 1, 12, 192 ] ] == [ 13, 92, 183 ]