Add a generic "object decorator" interface, and make object refs use it

This allows you to add an arbitrary "decoration" of your choice to any
object.  It's a space- and time-efficient way to add information to
arbitrary objects, especially if most objects probably do not have the
decoration.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -283,7 +283,7 @@ LIB_H = \
 	diff.h object.h pack.h pkt-line.h quote.h refs.h list-objects.h sideband.h \
 	run-command.h strbuf.h tag.h tree.h git-compat-util.h revision.h \
 	tree-walk.h log-tree.h dir.h path-list.h unpack-trees.h builtin.h \
-	utf8.h reflog-walk.h patch-ids.h
+	utf8.h reflog-walk.h patch-ids.h decorate.h
 
 DIFF_OBJS = \
 	diff.o diff-lib.o diffcore-break.o diffcore-order.o \
@@ -305,7 +305,7 @@ LIB_OBJS = \
 	write_or_die.o trace.o list-objects.o grep.o match-trees.o \
 	alloc.o merge-file.o path-list.o help.o unpack-trees.o $(DIFF_OBJS) \
 	color.o wt-status.o archive-zip.o archive-tar.o shallow.o utf8.o \
-	convert.o
+	convert.o decorate.o
 
 BUILTIN_OBJS = \
 	builtin-add.o \

decorate.c

@@ -0,0 +1,89 @@
+/*
+ * decorate.c - decorate a git object with some arbitrary
+ * data.
+ */
+#include "cache.h"
+#include "object.h"
+#include "decorate.h"
+
+static unsigned int hash_obj(struct object *obj, unsigned int n)
+{
+	unsigned int hash = *(unsigned int *)obj->sha1;
+	return hash % n;
+}
+
+static void *insert_decoration(struct decoration *n, struct object *base, void *decoration)
+{
+	int size = n->size;
+	struct object_decoration *hash = n->hash;
+	int j = hash_obj(base, size);
+
+	while (hash[j].base) {
+		if (hash[j].base == base) {
+			void *old = hash[j].decoration;
+			hash[j].decoration = decoration;
+			return old;
+		}
+		j++;
+		if (++j >= size)
+			j = 0;
+	}
+	hash[j].base = base;
+	hash[j].decoration = decoration;
+	n->nr++;
+	return NULL;
+}
+
+static void grow_decoration(struct decoration *n)
+{
+	int i;
+	int old_size = n->size;
+	struct object_decoration *old_hash;
+
+	old_size = n->size;
+	old_hash = n->hash;
+
+	n->size = (old_size + 1000) * 3 / 2;
+	n->hash = xcalloc(n->size, sizeof(struct object_decoration));
+	n->nr = 0;
+
+	for (i = 0; i < old_size; i++) {
+		struct object *base = old_hash[i].base;
+		void *decoration = old_hash[i].decoration;
+
+		if (!base)
+			continue;
+		insert_decoration(n, base, decoration);
+	}
+	free(old_hash);
+}
+
+/* Add a decoration pointer, return any old one */
+void *add_decoration(struct decoration *n, struct object *obj, void *decoration)
+{
+	int nr = n->nr + 1;
+
+	if (nr > n->size * 2 / 3)
+		grow_decoration(n);
+	return insert_decoration(n, obj, decoration);
+}
+
+/* Lookup a decoration pointer */
+void *lookup_decoration(struct decoration *n, struct object *obj)
+{
+	int j;
+
+	/* nothing to lookup */
+	if (!n->size)
+		return NULL;
+	j = hash_obj(obj, n->size);
+	for (;;) {
+		struct object_decoration *ref = n->hash + j;
+		if (ref->base == obj)
+			return ref->decoration;
+		if (!ref->base)
+			return NULL;
+		if (++j == n->size)
+			j = 0;
+	}
+}

decorate.h

@@ -0,0 +1,18 @@
+#ifndef DECORATE_H
+#define DECORATE_H
+
+struct object_decoration {
+	struct object *base;
+	void *decoration;
+};
+
+struct decoration {
+	const char *name;
+	unsigned int size, nr;
+	struct object_decoration *hash;
+};
+
+extern void *add_decoration(struct decoration *n, struct object *obj, void *decoration);
+extern void *lookup_decoration(struct decoration *n, struct object *obj);
+
+#endif

object-refs.c

@@ -1,75 +1,20 @@
 #include "cache.h"
 #include "object.h"
+#include "decorate.h"
 
 int track_object_refs = 0;
 
-static unsigned int refs_hash_size, nr_object_refs;
-static struct object_refs **refs_hash;
+static struct decoration ref_decorate;
 
-static unsigned int hash_obj(struct object *obj, unsigned int n)
+struct object_refs *lookup_object_refs(struct object *base)
 {
-	unsigned int hash = *(unsigned int *)obj->sha1;
-	return hash % n;
+	return lookup_decoration(&ref_decorate, base);
 }
 
-static void insert_ref_hash(struct object_refs *ref, struct object_refs **hash, unsigned int size)
+static void add_object_refs(struct object *obj, struct object_refs *refs)
 {
-	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;
+	if (add_decoration(&ref_decorate, obj, refs))
+		die("object %s tried to add refs twice!", sha1_to_hex(obj->sha1));
 }
 
 struct object_refs *alloc_object_refs(unsigned count)

object.h

@@ -8,7 +8,6 @@ struct object_list {
 
 struct object_refs {
 	unsigned count;
-	struct object *base;
 	struct object *ref[FLEX_ARRAY]; /* more */
 };