BN_is_bit_set
int BN_is_bit_set(const BIGNUM */*a*/, int /*n*/);
while (!BN_is_bit_set(p->number, 0)) {
if (BN_is_bit_set(p->number, 0)) {
ch |= BN_is_bit_set(v, numbits-i-1) << (7 - i);