a[4] b[4] a_invert b_invert c_in operation[2] c_out result[4]
# Test AND mode
0000 0000 0        0        x    00           x     0000
1100 1010 0        0        x    00           x     1000

# Test OR mode
0000 0000 0        0        x    01           x     0000
1100 1010 0        0        x    01           x     1110

# Test NAND mode
# Fill these in if you'd like

# Test addition
0001 0110 0        0        0    10           0     0111
0111 0100 0        0        0    10           0     1011
1001 0111 0        0        0    10           1     0000

# Test subtraction
0100 0011 0        1        1    10           1     0001
0000 1111 0        1        1    10           0     0001