radix_pos
node = node->slots[radix_pos(index, height--)];
idx = radix_pos(index, 0);
idx = radix_pos(index, height);
idx = radix_pos(index, height);
idx = radix_pos(index, height);
idx = radix_pos(index, 0);
node = node->slots[radix_pos(index, height--)];
item = node->slots[radix_pos(index, 0)];
int pos = radix_pos(index, height);