bit_ff_at_
*(_resultp) = bit_ff_at_((_bitstr), (_start), (_nbits), (_match))
*(_resultp) = bit_ff_at_((_bitstr), (_start), (_nbits), 1)
*(_resultp) = bit_ff_at_((_bitstr), (_start), (_nbits), 0)
*(_resultp) = bit_ff_at_((_bitstr), 0, (_nbits), 1)
*(_resultp) = bit_ff_at_((_bitstr), 0, (_nbits), 0)
for ((_iter) = bit_ff_at_((_bitstr), (_start), (_nbits), 1); \
(_iter) = bit_ff_at_((_bitstr), (_iter) + 1, (_nbits), 1))
for ((_iter) = bit_ff_at_((_bitstr), (_start), (_nbits), 0); \
(_iter) = bit_ff_at_((_bitstr), (_iter) + 1, (_nbits), 0))