The Hamming distance is the number of differences
of the bits of the two arguments.
18 is written 0x12 in base 16 and 0b010010 in base 2,
56 is written 0x38 in base 16 and 0b111000 in base 2,
hamdist(18,56) is equal to 1+0+1+0+1+0 and so is equal to 3.