BN_sub
BN_sub(i, i, one);
BN_sub(i, i, one);
int BN_sub(BIGNUM */*r*/, const BIGNUM */*a*/, const BIGNUM */*b*/);
if (BN_sub(t1, max, BN_value_50()) == 0)
bn_check(BN_sub(r->number, b->number, a->number));
bn_check(BN_sub(r, x, y));
bn_check(BN_sub(fract_part->number, fract_part->number,