1. #define bswap(data, m, n) \
    2.     ((data >> m) == (data >> n) ? data : data ^ ((1 << m) | (1 << n)))
    4.     0 1 0 1 0 1 0 1
    5.     0 0 0 0 0 1 1 0
    6.  ^ -----------------
    7.     0 1 0 1 0 0 1 1