bt_shift_leaf
bt_shift_leaf(tree, leaf, 0, idx, 1, BSD_RIGHT);
bt_shift_leaf(tree, leaf, idx + 1, hdr->bth_count - idx - 1,
bt_shift_leaf(tree, leaf, n, idx, n, BSD_LEFT);
bt_shift_leaf(tree, leaf, idx, hdr->bth_count - idx, n,
bt_shift_leaf(tree, leaf, fn, idx, fn, BSD_LEFT);
bt_shift_leaf(tree, leaf, fn + idx, hdr->bth_count - idx,
bt_shift_leaf(tree, leaf, 0, idx, n, BSD_RIGHT);
bt_shift_leaf(tree, leaf, idx + n, hdr->bth_count - idx - n, n,