Add initial implementation of a reference counting trie.

include/ref_trie.h

@@ -0,0 +1,80 @@
+#ifndef LIBABACUS_REF_TRIE_H
+#define LIBABACUS_REF_TRIE_H
+
+#include "refcount.h"
+#include "result.h"
+
+/**
+ * A node in the trie.
+ * unlike the normal libab_trie,
+ * this trie only has at most one value for each key.
+ */
+struct libab_ref_trie_node_s {
+    /**
+     * The next child of this trie node, which represents
+     * a letter the same distance from the beginning.
+     */
+    struct libab_ref_trie_node_s* next;
+    /**
+     * The child of this node, which represents a letter
+     * one further away than this node, with the same prefix.
+     */
+    struct libab_ref_trie_node_s* child;
+    /**
+     * The key of this node.
+     */
+    char key;
+    /**
+     * The reference pointed to by this node.
+     */
+    libab_ref ref;
+};
+
+/**
+ * The struct that holds the trie.
+ */
+struct libab_ref_trie_s {
+    /**
+     * The first node in the trie.
+     */
+    struct libab_ref_trie_node_s* head;
+    /**
+     * Reference (initialized to NULL) returned
+     * if no key is found.
+     */
+    libab_ref null_ref;
+};
+
+typedef struct libab_ref_trie_node_s libab_ref_trie_node;
+typedef struct libab_ref_trie_s libab_ref_trie;
+
+/**
+ * Initializes the trie with no nodes.
+ * @param trie the trie to initialize.
+ */
+void libab_ref_trie_init(libab_ref_trie* trie);
+/**
+ * Stores a reference counted value into the trie.
+ * This releases the reference for the given key, if one
+ * already exists. This increments the refcoutn.
+ * @param trie the trie to insert into.
+ * @param key the key to insert under.
+ * @param ref the reference to insert.
+ * @return the result of the insertion.
+ */
+libab_result libab_ref_trie_put(libab_ref_trie* trie, const char* key, libab_ref* ref);
+/**
+ * Retreives a reference under the given key in the trie.
+ * @param trie the trie to retreive from.
+ * @param key the key to look under.
+ * @return a reference stored under the given key. This can be a NULL reference.
+ */
+const libab_ref* libab_ref_trie_get(const libab_ref_trie* trie, const char* key);
+/**
+ * Releases the trie, decrementing the refcounts of all
+ * the values stored inside.
+ * @param trie the trie to release.
+ */
+void libab_ref_trie_free(libab_ref_trie* trie);
+
+#endif