x = 0xBEEF
y = 0x00000000000000000000000000000000000000000000000000
z = 0xCAFE
zero_extend(z) = 0x0000CAFE
q = 0xABFEEDDEADBEEFCAFE
k = 0xFF
k + k = 0xFE
0xFF + 1 = 0x00
0xFF + 2 = 0x01
0xFF + 3 = 0x02