diff --git a/hash.c b/hash.c
new file mode 100644
index 0000000..7b492d4
--- /dev/null
+++ b/hash.c
@@ -0,0 +1,110 @@
+/*
+ * Some generic hashing helpers.
+ */
+#include "cache.h"
+#include "hash.h"
+
+/*
+ * Look up a hash entry in the hash table. Return the pointer to
+ * the existing entry, or the empty slot if none existed. The caller
+ * can then look at the (*ptr) to see whether it existed or not.
+ */
+static struct hash_table_entry *lookup_hash_entry(unsigned int hash, struct hash_table *table)
+{
+	unsigned int size = table->size, nr = hash % size;
+	struct hash_table_entry *array = table->array;
+
+	while (array[nr].ptr) {
+		if (array[nr].hash == hash)
+			break;
+		nr++;
+		if (nr >= size)
+			nr = 0;
+	}
+	return array + nr;
+}
+
+
+/*
+ * Insert a new hash entry pointer into the table.
+ *
+ * If that hash entry already existed, return the pointer to
+ * the existing entry (and the caller can create a list of the
+ * pointers or do anything else). If it didn't exist, return
+ * NULL (and the caller knows the pointer has been inserted).
+ */
+static void **insert_hash_entry(unsigned int hash, void *ptr, struct hash_table *table)
+{
+	struct hash_table_entry *entry = lookup_hash_entry(hash, table);
+
+	if (!entry->ptr) {
+		entry->ptr = ptr;
+		entry->hash = hash;
+		table->nr++;
+		return NULL;
+	}
+	return &entry->ptr;
+}
+
+static void grow_hash_table(struct hash_table *table)
+{
+	unsigned int i;
+	unsigned int old_size = table->size, new_size;
+	struct hash_table_entry *old_array = table->array, *new_array;
+
+	new_size = alloc_nr(old_size);
+	new_array = xcalloc(sizeof(struct hash_table_entry), new_size);
+	table->size = new_size;
+	table->array = new_array;
+	table->nr = 0;
+	for (i = 0; i < old_size; i++) {
+		unsigned int hash = old_array[i].hash;
+		void *ptr = old_array[i].ptr;
+		if (ptr)
+			insert_hash_entry(hash, ptr, table);
+	}
+	free(old_array);
+}
+
+void *lookup_hash(unsigned int hash, struct hash_table *table)
+{
+	if (!table->array)
+		return NULL;
+	return &lookup_hash_entry(hash, table)->ptr;
+}
+
+void **insert_hash(unsigned int hash, void *ptr, struct hash_table *table)
+{
+	unsigned int nr = table->nr;
+	if (nr >= table->size/2)
+		grow_hash_table(table);
+	return insert_hash_entry(hash, ptr, table);
+}
+
+int for_each_hash(struct hash_table *table, int (*fn)(void *))
+{
+	int sum = 0;
+	unsigned int i;
+	unsigned int size = table->size;
+	struct hash_table_entry *array = table->array;
+
+	for (i = 0; i < size; i++) {
+		void *ptr = array->ptr;
+		array++;
+		if (ptr) {
+			int val = fn(ptr);
+			if (val < 0)
+				return val;
+			sum += val;
+		}
+	}
+	return sum;
+}
+
+void free_hash(struct hash_table *table)
+{
+	free(table->array);
+	table->array = NULL;
+	table->size = 0;
+	table->nr = 0;
+}