BN_cmp() compares the numbers a and b. BN_ucmp() compares their absolute values.BN_is_zero(), BN_is_one() and BN_is_word() test if a equals 0, 1, or w respectively. BN_is_odd() tests if a is odd.
BN_is_zero(), BN_is_one(), BN_is_word() and BN_is_odd() are macros.