bit_nset
bit_nset(bs, 1, TEST_LENGTH - 2);
bit_nset(bs, 0, TEST_LENGTH - 2);
bit_nset(bs, i, TEST_LENGTH - 1);
bit_nset(bs, 0, TEST_LENGTH - 1);
bit_nset(bs, 0, TEST_LENGTH - 1 - i);
bit_nset(bs, 0, TEST_LENGTH - 1);
bit_nset(bs, 0, TEST_LENGTH - 1);
bit_nset(bs, i, i);
bit_nset(bs, i, i);
bit_nset(bs, TEST_LENGTH - 1 - i, TEST_LENGTH - 1 - i);
bit_nset(bs, i++, i++);
bit_nset(bs, y, y + ny - 1);
bit_nset(bits, start, stop);