a = 00
b = 00
r = 00

a = 00
b = ffffffff00000001000000000000000000000000fffffffffffffffffffffffe
r = 00

a = 01
b = ffffffff00000001000000000000000000000000fffffffffffffffffffffffe
r = fffffffd00000002fffffffdffffffff00000001fffffffcffffffff

a = 02
b = ffffffff00000001000000000000000000000000fffffffffffffffffffffffe
r = 01fffffffa00000005fffffffbfffffffe00000003fffffff9fffffffe

a = 03
b = ffffffff00000001000000000000000000000000fffffffffffffffffffffffe
r = 02fffffff700000008fffffff9fffffffd00000005fffffff6fffffffd

a = 7fffffff800000008000000000000000000000007fffffffffffffffffffffff
b = 02
r = fffffffd00000002fffffffdffffffff00000001fffffffcffffffff

a = 7fffffff80000000800000000000000000000000800000000000000000000000
b = 02
r = fffffffe00000003fffffffd0000000200000001fffffffe0000000300000000

a = 8000000000000000000000000000000000000000000000000000000000000000
b = 02
r = 01