/* Color of a red-black node. */
enum prb_color
  {
    PRB_BLACK,   /* Black. */
    PRB_RED      /* Red. */
  };

/* A red-black tree with parent pointers node. */
struct prb_node
  {
    struct prb_node *prb_link[2];  /* Subtrees. */
    struct prb_node *prb_parent;   /* Parent. */
    void *prb_data;                /* Pointer to data. */
    unsigned char prb_color;       /* Color. */
  };