TREE(3)                 NetBSD Library Functions Manual                TREE(3)

NAME
     SPLAY_PROTOTYPE, SPLAY_GENERATE, SPLAY_ENTRY, SPLAY_HEAD,
     SPLAY_INITIALIZER, SPLAY_ROOT, SPLAY_EMPTY, SPLAY_NEXT, SPLAY_MIN,
     SPLAY_MAX, SPLAY_FIND, SPLAY_LEFT, SPLAY_RIGHT, SPLAY_FOREACH,
     SPLAY_INIT, SPLAY_INSERT, SPLAY_REMOVE, RB_PROTOTYPE,
     RB_PROTOTYPE_STATIC, RB_GENERATE, RB_GENERATE_STATIC, RB_ENTRY, RB_HEAD,
     RB_INITIALIZER, RB_ROOT, RB_EMPTY, RB_NEXT, RB_PREV, RB_MIN, RB_MAX,
     RB_FIND, RB_NFIND, RB_LEFT, RB_RIGHT, RB_PARENT, RB_FOREACH,
     RB_FOREACH_SAFE, RB_FOREACH_REVERSE, RB_FOREACH_REVERSE_SAFE, RB_INIT,
     RB_INSERT, RB_REMOVE -- implementations of splay and red-black trees

SYNOPSIS
     #include <sys/tree.h>

     SPLAY_PROTOTYPE(NAME, TYPE, FIELD, CMP);

     SPLAY_GENERATE(NAME, TYPE, FIELD, CMP);

     SPLAY_ENTRY(TYPE);

     SPLAY_HEAD(HEADNAME, TYPE);

     struct TYPE *
     SPLAY_INITIALIZER(SPLAY_HEAD *head);

     SPLAY_ROOT(SPLAY_HEAD *head);

     int
     SPLAY_EMPTY(SPLAY_HEAD *head);

     struct TYPE *
     SPLAY_NEXT(NAME, SPLAY_HEAD *head, struct TYPE *elm);

     struct TYPE *
     SPLAY_MIN(NAME, SPLAY_HEAD *head);

     struct TYPE *
     SPLAY_MAX(NAME, SPLAY_HEAD *head);

     struct TYPE *
     SPLAY_FIND(NAME, SPLAY_HEAD *head, struct TYPE *elm);

     struct TYPE *
     SPLAY_LEFT(struct TYPE *elm, SPLAY_ENTRY NAME);

     struct TYPE *
     SPLAY_RIGHT(struct TYPE *elm, SPLAY_ENTRY NAME);

     SPLAY_FOREACH(VARNAME, NAME, SPLAY_HEAD *head);

     void
     SPLAY_INIT(SPLAY_HEAD *head);

     struct TYPE *
     SPLAY_INSERT(NAME, SPLAY_HEAD *head, struct TYPE *elm);

     struct TYPE *
     SPLAY_REMOVE(NAME, SPLAY_HEAD *head, struct TYPE *elm);

     RB_PROTOTYPE(NAME, TYPE, FIELD, CMP);

     RB_PROTOTYPE_STATIC(NAME, TYPE, FIELD, CMP);

     RB_GENERATE(NAME, TYPE, FIELD, CMP);

     RB_GENERATE_STATIC(NAME, TYPE, FIELD, CMP);

     RB_ENTRY(TYPE);

     RB_HEAD(HEADNAME, TYPE);

     RB_INITIALIZER(RB_HEAD *head);

     struct TYPE *
     RB_ROOT(RB_HEAD *head);

     int
     RB_EMPTY(RB_HEAD *head);

     struct TYPE *
     RB_NEXT(NAME, RB_HEAD *head, struct TYPE *elm);

     struct TYPE *
     RB_PREV(NAME, RB_HEAD *head, struct TYPE *elm);

     struct TYPE *
     RB_MIN(NAME, RB_HEAD *head);

     struct TYPE *
     RB_MAX(NAME, RB_HEAD *head);

     struct TYPE *
     RB_FIND(NAME, RB_HEAD *head, struct TYPE *elm);

     struct TYPE *
     RB_NFIND(NAME, RB_HEAD *head, struct TYPE *elm);

     struct TYPE *
     RB_LEFT(struct TYPE *elm, RB_ENTRY NAME);

     struct TYPE *
     RB_RIGHT(struct TYPE *elm, RB_ENTRY NAME);

     struct TYPE *
     RB_PARENT(struct TYPE *elm, RB_ENTRY NAME);

     RB_FOREACH(VARNAME, NAME, RB_HEAD *head);

     RB_FOREACH_SAFE(VARNAME, NAME, RB_HEAD *head, TEMP_VARNAME);

     RB_FOREACH_REVERSE(VARNAME, NAME, RB_HEAD *head);

     RB_FOREACH_REVERSE_SAFE(VARNAME, NAME, RB_HEAD *head, TEMP_VARNAME);

     void
     RB_INIT(RB_HEAD *head);

     struct TYPE *
     RB_INSERT(NAME, RB_HEAD *head, struct TYPE *elm);

     struct TYPE *
     RB_REMOVE(NAME, RB_HEAD *head, struct TYPE *elm);

DESCRIPTION
     This is a legacy interface; for new code, rbtree(3) is preferred.

     These macros define data structures for different types of trees: splay
     trees and red-black trees.

     In the macro definitions, TYPE is the name tag of a user defined struc-
     ture that must contain a field named FIELD, of type SPLAY_ENTRY or
     RB_ENTRY.  The argument HEADNAME is the name tag of a user defined struc-
     ture that must be declared using the macros SPLAY_HEAD() or RB_HEAD().
     The argument NAME has to be a unique name prefix for every tree that is
     defined.

     The function prototypes are declared with SPLAY_PROTOTYPE, RB_PROTOTYPE,
     or RB_PROTOTYPE_STATIC.  The function bodies are generated with
     SPLAY_GENERATE, RB_GENERATE, or RB_GENERATE_STATIC.  See the examples
     below for further explanation of how these macros are used.

SPLAY TREES
     A splay tree is a self-organizing data structure.  Every operation on the
     tree causes a splay to happen.  The splay moves the requested node to the
     root of the tree and partly rebalances it.

     This has the benefit that request locality causes faster lookups as the
     requested nodes move to the top of the tree.  On the other hand, every
     lookup causes memory writes.

     The Balance Theorem bounds the total access time for m operations and n
     inserts on an initially empty tree as O((m + n)lg n).  The amortized cost
     for a sequence of m accesses to a splay tree is O(lg n).

     A splay tree is headed by a structure defined by the SPLAY_HEAD() macro.
     A SPLAY_HEAD structure is declared as follows:

           SPLAY_HEAD(HEADNAME, TYPE) head;

     where HEADNAME is the name of the structure to be defined, and struct
     TYPE is the type of the elements to be inserted into the tree.

     The SPLAY_ENTRY() macro declares a structure that allows elements to be
     connected in the tree.

     In order to use the functions that manipulate the tree structure, their
     prototypes need to be declared with the SPLAY_PROTOTYPE() macro, where
     NAME is a unique identifier for this particular tree.  The TYPE argument
     is the type of the structure that is being managed by the tree.  The
     FIELD argument is the name of the element defined by SPLAY_ENTRY().

     The function bodies are generated with the SPLAY_GENERATE() macro.  It
     takes the same arguments as the SPLAY_PROTOTYPE() macro, but should be
     used only once.

     Finally, the CMP argument is the name of a function used to compare tree
     nodes with each other.  The function takes two arguments of type struct
     TYPE *.  If the first argument is smaller than the second, the function
     returns a value smaller than zero.  If they are equal, the function
     returns zero.  Otherwise, it should return a value greater than zero.
     The compare function defines the order of the tree elements.

     The SPLAY_INIT() macro initializes the tree referenced by head.

     The splay tree can also be initialized statically by using the
     SPLAY_INITIALIZER() macro like this:

           SPLAY_HEAD(HEADNAME, TYPE) head = SPLAY_INITIALIZER(&head);

     The SPLAY_INSERT() macro inserts the new element elm into the tree.  Upon
     success, NULL is returned.  If a matching element already exists in the
     tree, the insertion is aborted, and a pointer to the existing element is
     returned.

     The SPLAY_REMOVE() macro removes the element elm from the tree pointed by
     head.  Upon success, a pointer to the removed element is returned.  NULL
     is returned if elm is not present in the tree.

     The SPLAY_FIND() macro can be used to find a particular element in the
     tree.

           struct TYPE find, *res;
           find.key = 30;
           res = SPLAY_FIND(NAME, &head, &find);

     The SPLAY_ROOT(), SPLAY_MIN(), SPLAY_MAX(), and SPLAY_NEXT() macros can
     be used to traverse the tree:

           for (np = SPLAY_MIN(NAME, &head); np != NULL; np = SPLAY_NEXT(NAME, &head, np))

     Or, for simplicity, one can use the SPLAY_FOREACH() macro:

           SPLAY_FOREACH(np, NAME, &head)

     The SPLAY_EMPTY() macro should be used to check whether a splay tree is
     empty.

RED-BLACK TREES
     A red-black tree is a binary search tree with the node color as an extra
     attribute.  It fulfills a set of conditions:

           1.   every search path from the root to a leaf consists of the same
                number of black nodes,
           2.   each red node (except for the root) has a black parent,
           3.   each leaf node is black.

     Every operation on a red-black tree is bounded as O(lg n).  The maximum
     height of a red-black tree is 2lg (n+1).

     A red-black tree is headed by a structure defined by the RB_HEAD() macro.
     A RB_HEAD structure is declared as follows:

           RB_HEAD(HEADNAME, TYPE) head;

     where HEADNAME is the name of the structure to be defined, and struct
     TYPE is the type of the elements to be inserted into the tree.

     The RB_ENTRY() macro declares a structure that allows elements to be con-
     nected in the tree.

     In order to use the functions that manipulate the tree structure, their
     prototypes need to be declared with the RB_PROTOTYPE() or
     RB_PROTOTYPE_STATIC() macros, where NAME is a unique identifier for this
     particular tree.  The TYPE argument is the type of the structure that is
     being managed by the tree.  The FIELD argument is the name of the element
     defined by RB_ENTRY().

     The function bodies are generated with the RB_GENERATE() or
     RB_GENERATE_STATIC() macros.  These macros take the same arguments as the
     RB_PROTOTYPE() and RB_PROTOTYPE_STATIC() macros, but should be used only
     once.

     Finally, the CMP argument is the name of a function used to compare
     trees' nodes with each other.  The function takes two arguments of type
     struct TYPE *.  If the first argument is smaller than the second, the
     function returns a value smaller than zero.  If they are equal, the func-
     tion returns zero.  Otherwise, it should return a value greater than
     zero.  The compare function defines the order of the tree elements.

     The RB_INIT() macro initializes the tree referenced by head.

     The red-black tree can also be initialized statically by using the
     RB_INITIALIZER() macro like this:

           RB_HEAD(HEADNAME, TYPE) head = RB_INITIALIZER(&head);

     The RB_INSERT() macro inserts the new element elm into the tree.  Upon
     success, NULL is returned.  If a matching element already exists in the
     tree, the insertion is aborted, and a pointer to the existing element is
     returned.

     The RB_REMOVE() macro removes the element elm from the tree pointed to by
     head.  The element must be present in that tree.  RB_REMOVE() returns
     elm.

     The RB_FIND() macro can be used to find a particular element in the tree.
     and RB_NFIND() macros can be used to find a particular element in the
     tree.  RB_FIND() finds the node with the same key as elm.  RB_NFIND()
     finds the first node greater than or equal to the search key.

           struct TYPE find, *res;
           find.key = 30;
           res = RB_FIND(NAME, &head, &find);

     The RB_ROOT(), RB_MIN(), RB_MAX(), RB_NEXT(), and RB_PREV() macros can be
     used to traverse the tree:

           for (np = RB_MIN(NAME, &head); np != NULL; np = RB_NEXT(NAME, &head, np))

     Or, for simplicity, one can use the RB_FOREACH() or RB_FOREACH_REVERSE()
     macros:

           RB_FOREACH(np, NAME, &head)

     The macros RB_FOREACH_SAFE() and RB_FOREACH_REVERSE_SAFE() traverse the
     tree referenced by head in a forward or reverse direction respectively,
     assigning each element in turn to np.  However, unlike their unsafe coun-
     terparts, they permit both the removal of np as well as freeing it from
     within the loop safely without interfering with the traversal.

     The RB_EMPTY() macro should be used to check whether a red-black tree is
     empty.

EXAMPLES
     The following example demonstrates how to declare a red-black tree hold-
     ing integers.  Values are inserted into it and the contents of the tree
     are printed in order.  Lastly, the internal structure of the tree is
     printed.

        #include <sys/tree.h>
        #include <err.h>
        #include <stdio.h>
        #include <stdlib.h>

        struct node {
                RB_ENTRY(node) entry;
                int i;
        };

        int
        intcmp(struct node *e1, struct node *e2)
        {
                return (e1->i < e2->i ? -1 : e1->i > e2->i);
        }

        RB_HEAD(inttree, node) head = RB_INITIALIZER(&head);
        RB_GENERATE(inttree, node, entry, intcmp)

        int testdata[] = {
                20, 16, 17, 13, 3, 6, 1, 8, 2, 4, 10, 19, 5, 9, 12, 15, 18,
                7, 11, 14
        };

        void
        print_tree(struct node *n)
        {
                struct node *left, *right;

                if (n == NULL) {
                        printf("nil");
                        return;
                }
                left = RB_LEFT(n, entry);
                right = RB_RIGHT(n, entry);
                if (left == NULL && right == NULL)
                        printf("%d", n->i);
                else {
                        printf("%d(", n->i);
                        print_tree(left);
                        printf(",");
                        print_tree(right);
                        printf(")");
                }
        }

        int
        main()
        {
                int i;
                struct node *n;

                for (i = 0; i < sizeof(testdata) / sizeof(testdata[0]); i++) {
                        if ((n = malloc(sizeof(struct node))) == NULL)
                                err(1, NULL);
                        n->i = testdata[i];
                        RB_INSERT(inttree, &head, n);
                }

                RB_FOREACH(n, inttree, &head) {
                        printf("%d\n", n->i);
                }
                print_tree(RB_ROOT(&head));
                printf("\n");
                return (0);
        }

NOTES
     Some of these macros or functions perform no error checking, and invalid
     usage leads to undefined behaviour.  In the case of macros or functions
     that expect their arguments to be elements that are present in the tree,
     passing an element that is not present in the tree is invalid.

     Trying to free a tree in the following way is a common error:

           SPLAY_FOREACH(var, NAME, &head) {
                   SPLAY_REMOVE(NAME, &head, var);
                   free(var);
           }
           free(head);

     Since var is free'd, the FOREACH() macro refers to a pointer that may
     have been reallocated already.  Proper code needs a second variable.

           for (var = SPLAY_MIN(NAME, &head); var != NULL; var = nxt) {
                   nxt = SPLAY_NEXT(NAME, &head, var);
                   SPLAY_REMOVE(NAME, &head, var);
                   free(var);
           }

AUTHORS
     The author of the tree macros is Niels Provos.

NetBSD 7.1                       July 9, 2011                       NetBSD 7.1

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