These functions perform arithmetic operations on BIGNUMs with unsigned integers. They are much more efficient than the normal BIGNUM arithmetic operations.
BN_add_word() adds w to a ("a+=w").
BN_sub_word() subtracts w from a ("a-=w").
BN_mul_word() multiplies a and w ("a*=w").
BN_div_word() divides a by w ("a/=w") and returns the remainder.
BN_mod_word() returns the remainder of a divided by w ("a%w").
For BN_div_word() and BN_mod_word(), w must not be 0.