1 files changed, 50 insertions, 0 deletions
diff --git a/hash.h b/hash.h
new file mode 100644
index 0000000000..1d43ac0ba0
--- /dev/null
+++ b/hash.h
@@ -0,0 +1,50 @@
+#ifndef HASH_H
+#define HASH_H
+
+/*
+ * These are some simple generic hash table helper functions.
+ * Not necessarily suitable for all users, but good for things
+ * where you want to just keep track of a list of things, and
+ * have a good hash to use on them.
+ *
+ * It keeps the hash table at roughly 50-75% free, so the memory
+ * cost of the hash table itself is roughly
+ *
+ *	3 * 2*sizeof(void *) * nr_of_objects
+ *
+ * bytes.
+ *
+ * FIXME: on 64-bit architectures, we waste memory. It would be
+ * good to have just 32-bit pointers, requiring a special allocator
+ * for hashed entries or something.
+ */
+struct hash_table_entry {
+	unsigned int hash;
+	void *ptr;
+};
+
+struct hash_table {
+	unsigned int size, nr;
+	struct hash_table_entry *array;
+};
+
+extern void *lookup_hash(unsigned int hash, const struct hash_table *table);
+extern void **insert_hash(unsigned int hash, void *ptr, struct hash_table *table);
+extern int for_each_hash(const struct hash_table *table, int (*fn)(void *, void *), void *data);
+extern void free_hash(struct hash_table *table);
+
+static inline void init_hash(struct hash_table *table)
+{
+	table->size = 0;
+	table->nr = 0;
+	table->array = NULL;
+}
+
+static inline void preallocate_hash(struct hash_table *table, unsigned int elts)
+{
+	assert(table->size == 0 && table->nr == 0 && table->array == NULL);
+	table->size = elts * 2;
+	table->array = xcalloc(sizeof(struct hash_table_entry), table->size);
+}
+
+#endif