code table:
0 1 0 1 
0 0 0 1 
0 0 1 1 
0 0 1 0 
1 0 1 0 
1 0 1 1 
1 1 1 1 
1 1 0 1 
1 0 0 1 
1 0 0 0 
0 0 0 0 
0 1 0 0 
1 1 0 0 
1 1 1 0 
0 1 1 0 
0 1 1 1 
ch table:
0 1 0 0 
0 0 1 0 
0 0 0 1 
1 0 0 0 
0 0 0 1 
0 1 0 0 
0 0 1 0 
0 1 0 0 
0 0 0 1 
1 0 0 0 
0 1 0 0 
1 0 0 0 
0 0 1 0 
1 0 0 0 
0 0 0 1 
0 0 1 0 
stat (bit number: count of changes):  {0: 4, 1: 4, 2: 4, 3: 4}