vcs-svn/trp.txt

   1 Motivation
   2 ==========
   3
   4 Treaps provide a memory-efficient binary search tree structure.
   5 Insertion/deletion/search are about as about as fast in the average
   6 case as red-black trees and the chances of worst-case behavior are
   7 vanishingly small, thanks to (pseudo-)randomness.  The bad worst-case
   8 behavior is a small price to pay, given that treaps are much simpler
   9 to implement.
  10
  11 API
  12 ===
  13
  14 The trp API generates a data structure and functions to handle a
  15 large growing set of objects stored in a pool.
  16
  17 The caller:
  18
  19 . Specifies parameters for the generated functions with the
  20   trp_gen(static, foo_, ...) macro.
  21
  22 . Allocates a `struct trp_root` variable and sets it to {~0}.
  23
  24 . Adds new nodes to the set using `foo_insert`.  Any pointers
  25   to existing nodes cannot be relied upon any more, so the caller
  26   might retrieve them anew with `foo_pointer`.
  27
  28 . Can find a specific item in the set using `foo_search`.
  29
  30 . Can iterate over items in the set using `foo_first` and `foo_next`.
  31
  32 . Can remove an item from the set using `foo_remove`.
  33
  34 Example:
  35
  36 ----
  37 struct ex_node {
  38         const char *s;
  39         struct trp_node ex_link;
  40 };
  41 static struct trp_root ex_base = {~0};
  42 obj_pool_gen(ex, struct ex_node, 4096);
  43 trp_gen(static, ex_, struct ex_node, ex_link, ex, strcmp)
  44 struct ex_node *item;
  45
  46 item = ex_pointer(ex_alloc(1));
  47 item->s = "hello";
  48 ex_insert(&ex_base, item);
  49 item = ex_pointer(ex_alloc(1));
  50 item->s = "goodbye";
  51 ex_insert(&ex_base, item);
  52 for (item = ex_first(&ex_base); item; item = ex_next(&ex_base, item))
  53         printf("%s\n", item->s);
  54 ----
  55
  56 Functions
  57 ---------
  58
  59 trp_gen(attr, foo_, node_type, link_field, pool, cmp)::
  60
  61         Generate a type-specific treap implementation.
  62 +
  63 . The storage class for generated functions will be 'attr' (e.g., `static`).
  64 . Generated function names are prefixed with 'foo_' (e.g., `treap_`).
  65 . Treap nodes will be of type 'node_type' (e.g., `struct treap_node`).
  66   This type must be a struct with at least one `struct trp_node` field
  67   to point to its children.
  68 . The field used to access child nodes will be 'link_field'.
  69 . All treap nodes must lie in the 'pool' object pool.
  70 . Treap nodes must be totally ordered by the 'cmp' relation, with the
  71   following prototype:
  72 +
  73 int (*cmp)(node_type \*a, node_type \*b)
  74 +
  75 and returning a value less than, equal to, or greater than zero
  76 according to the result of comparison.
  77
  78 node_type {asterisk}foo_insert(struct trp_root *treap, node_type \*node)::
  79
  80         Insert node into treap.  If inserted multiple times,
  81         a node will appear in the treap multiple times.
  82 +
  83 The return value is the address of the node within the treap,
  84 which might differ from `node` if `pool_alloc` had to call
  85 `realloc` to expand the pool.
  86
  87 void foo_remove(struct trp_root *treap, node_type \*node)::
  88
  89         Remove node from treap.  Caller must ensure node is
  90         present in treap before using this function.
  91
  92 node_type *foo_search(struct trp_root \*treap, node_type \*key)::
  93
  94         Search for a node that matches key.  If no match is found,
  95         result is NULL.
  96
  97 node_type *foo_nsearch(struct trp_root \*treap, node_type \*key)::
  98
  99         Like `foo_search`, but if if the key is missing return what
 100         would be key's successor, were key in treap (NULL if no
 101         successor).
 102
 103 node_type *foo_first(struct trp_root \*treap)::
 104
 105         Find the first item from the treap, in sorted order.
 106
 107 node_type *foo_next(struct trp_root \*treap, node_type \*node)::
 108
 109         Find the next item.