Create a woodpecker script that takes 16-bit a and 16-bit b and calculates the 16-bit difference modulo 2**16 - 17 (65519) (a-b) % (2**16-17).
a<65519, b<65519 is guaranteed.
<low a hi> | <low b hi> | <low output hi>
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0000000000000000 | 0000000000000000 | 0000000000000000
0100000000000000 | 1000000000000000 | 1000000000000000
0000000000000000 | 1000000000000000 | 0111011111111111
1010001000000000 | 0010010110000000 | 0000100101111111
0111011111111111 | 1011011111111111 | 1000000000000000