1 files changed, 144 insertions, 0 deletions
diff --git a/object-refs.c b/object-refs.c
new file mode 100644
index 0000000000..98ea10005a
--- /dev/null
+++ b/object-refs.c
@@ -0,0 +1,144 @@
+#include "cache.h"
+#include "object.h"
+
+int track_object_refs = 0;
+
+static unsigned int refs_hash_size, nr_object_refs;
+static struct object_refs **refs_hash;
+
+static unsigned int hash_obj(struct object *obj, unsigned int n)
+{
+	unsigned int hash = *(unsigned int *)obj->sha1;
+	return hash % n;
+}
+
+static void insert_ref_hash(struct object_refs *ref, struct object_refs **hash, unsigned int size)
+{
+	int j = hash_obj(ref->base, size);
+
+	while (hash[j]) {
+		j++;
+		if (j >= size)
+			j = 0;
+	}
+	hash[j] = ref;
+}
+
+static void grow_refs_hash(void)
+{
+	int i;
+	int new_hash_size = (refs_hash_size + 1000) * 3 / 2;
+	struct object_refs **new_hash;
+
+	new_hash = xcalloc(new_hash_size, sizeof(struct object_refs *));
+	for (i = 0; i < refs_hash_size; i++) {
+		struct object_refs *ref = refs_hash[i];
+		if (!ref)
+			continue;
+		insert_ref_hash(ref, new_hash, new_hash_size);
+	}
+	free(refs_hash);
+	refs_hash = new_hash;
+	refs_hash_size = new_hash_size;
+}
+
+static void add_object_refs(struct object *obj, struct object_refs *ref)
+{
+	int nr = nr_object_refs + 1;
+
+	if (nr > refs_hash_size * 2 / 3)
+		grow_refs_hash();
+	ref->base = obj;
+	insert_ref_hash(ref, refs_hash, refs_hash_size);
+	nr_object_refs = nr;
+}
+
+struct object_refs *lookup_object_refs(struct object *obj)
+{
+	struct object_refs *ref;
+	int j;
+
+	/* nothing to lookup */
+	if (!refs_hash_size)
+		return NULL;
+	j = hash_obj(obj, refs_hash_size);
+	while ((ref = refs_hash[j]) != NULL) {
+		if (ref->base == obj)
+			break;
+		j++;
+		if (j >= refs_hash_size)
+			j = 0;
+	}
+	return ref;
+}
+
+struct object_refs *alloc_object_refs(unsigned count)
+{
+	struct object_refs *refs;
+	size_t size = sizeof(*refs) + count*sizeof(struct object *);
+
+	refs = xcalloc(1, size);
+	refs->count = count;
+	return refs;
+}
+
+static int compare_object_pointers(const void *a, const void *b)
+{
+	const struct object * const *pa = a;
+	const struct object * const *pb = b;
+	if (*pa == *pb)
+		return 0;
+	else if (*pa < *pb)
+		return -1;
+	else
+		return 1;
+}
+
+void set_object_refs(struct object *obj, struct object_refs *refs)
+{
+	unsigned int i, j;
+
+	/* Do not install empty list of references */
+	if (refs->count < 1) {
+		free(refs);
+		return;
+	}
+
+	/* Sort the list and filter out duplicates */
+	qsort(refs->ref, refs->count, sizeof(refs->ref[0]),
+	      compare_object_pointers);
+	for (i = j = 1; i < refs->count; i++) {
+		if (refs->ref[i] != refs->ref[i - 1])
+			refs->ref[j++] = refs->ref[i];
+	}
+	if (j < refs->count) {
+		/* Duplicates were found - reallocate list */
+		size_t size = sizeof(*refs) + j*sizeof(struct object *);
+		refs->count = j;
+		refs = xrealloc(refs, size);
+	}
+
+	for (i = 0; i < refs->count; i++)
+		refs->ref[i]->used = 1;
+	add_object_refs(obj, refs);
+}
+
+void mark_reachable(struct object *obj, unsigned int mask)
+{
+	const struct object_refs *refs;
+
+	if (!track_object_refs)
+		die("cannot do reachability with object refs turned off");
+	/* If we've been here already, don't bother */
+	if (obj->flags & mask)
+		return;
+	obj->flags |= mask;
+	refs = lookup_object_refs(obj);
+	if (refs) {
+		unsigned i;
+		for (i = 0; i < refs->count; i++)
+			mark_reachable(refs->ref[i], mask);
+	}
+}
+
+