Merge branch 'bw/object-id'

Conversion from uchar[20] to struct object_id continues.

* bw/object-id: (33 commits)
  diff: rename diff_fill_sha1_info to diff_fill_oid_info
  diffcore-rename: use is_empty_blob_oid
  tree-diff: convert path_appendnew to object_id
  tree-diff: convert diff_tree_paths to struct object_id
  tree-diff: convert try_to_follow_renames to struct object_id
  builtin/diff-tree: cleanup references to sha1
  diff-tree: convert diff_tree_sha1 to struct object_id
  notes-merge: convert write_note_to_worktree to struct object_id
  notes-merge: convert verify_notes_filepair to struct object_id
  notes-merge: convert find_notes_merge_pair_ps to struct object_id
  notes-merge: convert merge_from_diffs to struct object_id
  notes-merge: convert notes_merge* to struct object_id
  tree-diff: convert diff_root_tree_sha1 to struct object_id
  combine-diff: convert find_paths_* to struct object_id
  combine-diff: convert diff_tree_combined to struct object_id
  diff: convert diff_flush_patch_id to struct object_id
  patch-ids: convert to struct object_id
  diff: finish conversion for prepare_temp_file to struct object_id
  diff: convert reuse_worktree_file to struct object_id
  diff: convert fill_filespec to struct object_id
  ...

36 files changed, 539 insertions, 525 deletions

diff --git a/blame.c b/blame.c
index 843c845cba..194b58e960 100644
--- a/blame.c
+++ b/blame.c
@@ -556,9 +556,9 @@ static struct blame_origin *find_origin(struct commit *parent,
 	if (is_null_oid(&origin->commit->object.oid))
 		do_diff_cache(&parent->tree->object.oid, &diff_opts);
 	else
-		diff_tree_sha1(parent->tree->object.oid.hash,
-			       origin->commit->tree->object.oid.hash,
-			       "", &diff_opts);
+		diff_tree_oid(&parent->tree->object.oid,
+			      &origin->commit->tree->object.oid,
+			      "", &diff_opts);
 	diffcore_std(&diff_opts);
 
 	if (!diff_queued_diff.nr) {
@@ -625,9 +625,9 @@ static struct blame_origin *find_rename(struct commit *parent,
 	if (is_null_oid(&origin->commit->object.oid))
 		do_diff_cache(&parent->tree->object.oid, &diff_opts);
 	else
-		diff_tree_sha1(parent->tree->object.oid.hash,
-			       origin->commit->tree->object.oid.hash,
-			       "", &diff_opts);
+		diff_tree_oid(&parent->tree->object.oid,
+			      &origin->commit->tree->object.oid,
+			      "", &diff_opts);
 	diffcore_std(&diff_opts);
 
 	for (i = 0; i < diff_queued_diff.nr; i++) {
@@ -1247,7 +1247,7 @@ static void find_copy_in_parent(struct blame_scoreboard *sb,
 	/* Try "find copies harder" on new path if requested;
 	 * we do not want to use diffcore_rename() actually to
 	 * match things up; find_copies_harder is set only to
-	 * force diff_tree_sha1() to feed all filepairs to diff_queue,
+	 * force diff_tree_oid() to feed all filepairs to diff_queue,
 	 * and this code needs to be after diff_setup_done(), which
 	 * usually makes find-copies-harder imply copy detection.
 	 */
@@ -1259,9 +1259,9 @@ static void find_copy_in_parent(struct blame_scoreboard *sb,
 	if (is_null_oid(&target->commit->object.oid))
 		do_diff_cache(&parent->tree->object.oid, &diff_opts);
 	else
-		diff_tree_sha1(parent->tree->object.oid.hash,
-			       target->commit->tree->object.oid.hash,
-			       "", &diff_opts);
+		diff_tree_oid(&parent->tree->object.oid,
+			      &target->commit->tree->object.oid,
+			      "", &diff_opts);
 
 	if (!DIFF_OPT_TST(&diff_opts, FIND_COPIES_HARDER))
 		diffcore_std(&diff_opts);
diff --git a/builtin/am.c b/builtin/am.c
index 8881d73615..3985f9a89f 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -563,7 +563,7 @@ static int copy_notes_for_rebase(const struct am_state *state)
 			goto finish;
 		}
 
-		if (copy_note_for_rewrite(c, from_obj.hash, to_obj.hash))
+		if (copy_note_for_rewrite(c, &from_obj, &to_obj))
 			ret = error(_("Failed to copy notes from '%s' to '%s'"),
 					oid_to_hex(&from_obj), oid_to_hex(&to_obj));
 	}
diff --git a/builtin/commit.c b/builtin/commit.c
index ef52457eff..e3c9e190b0 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -1806,7 +1806,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		cfg = init_copy_notes_for_rewrite("amend");
 		if (cfg) {
 			/* we are amending, so current_head is not NULL */
-			copy_note_for_rewrite(cfg, current_head->object.oid.hash, oid.hash);
+			copy_note_for_rewrite(cfg, &current_head->object.oid, &oid);
 			finish_copy_notes_for_rewrite(cfg, "Notes added by 'git commit --amend'");
 		}
 		run_rewrite_hook(&current_head->object.oid, &oid);
diff --git a/builtin/diff-tree.c b/builtin/diff-tree.c
index 492245f428..1fd06eac4b 100644
--- a/builtin/diff-tree.c
+++ b/builtin/diff-tree.c
@@ -7,7 +7,7 @@
 
 static struct rev_info log_tree_opt;
 
-static int diff_tree_commit_sha1(const struct object_id *oid)
+static int diff_tree_commit_oid(const struct object_id *oid)
 {
 	struct commit *commit = lookup_commit_reference(oid);
 	if (!commit)
@@ -49,8 +49,8 @@ static int stdin_diff_trees(struct tree *tree1, const char *p)
 		return -1;
 	printf("%s %s\n", oid_to_hex(&tree1->object.oid),
 			  oid_to_hex(&tree2->object.oid));
-	diff_tree_sha1(tree1->object.oid.hash, tree2->object.oid.hash,
-		       "", &log_tree_opt.diffopt);
+	diff_tree_oid(&tree1->object.oid, &tree2->object.oid,
+		      "", &log_tree_opt.diffopt);
 	log_tree_diff_flush(&log_tree_opt);
 	return 0;
 }
@@ -98,7 +98,6 @@ static void diff_tree_tweak_rev(struct rev_info *rev, struct setup_revision_opt
 
 int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 {
-	int nr_sha1;
 	char line[1000];
 	struct object *tree1, *tree2;
 	static struct rev_info *opt = &log_tree_opt;
@@ -134,15 +133,14 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	 * second one is marked UNINTERESTING, we recover the original
 	 * order the user gave, i.e. "a..b", by swapping the trees.
 	 */
-	nr_sha1 = opt->pending.nr;
-	switch (nr_sha1) {
+	switch (opt->pending.nr) {
 	case 0:
 		if (!read_stdin)
 			usage(diff_tree_usage);
 		break;
 	case 1:
 		tree1 = opt->pending.objects[0].item;
-		diff_tree_commit_sha1(&tree1->oid);
+		diff_tree_commit_oid(&tree1->oid);
 		break;
 	case 2:
 		tree1 = opt->pending.objects[0].item;
@@ -150,9 +148,7 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 		if (tree2->flags & UNINTERESTING) {
 			SWAP(tree2, tree1);
 		}
-		diff_tree_sha1(tree1->oid.hash,
-			       tree2->oid.hash,
-			       "", &opt->diffopt);
+		diff_tree_oid(&tree1->oid, &tree2->oid, "", &opt->diffopt);
 		log_tree_diff_flush(opt);
 		break;
 	}
diff --git a/builtin/diff.c b/builtin/diff.c
index 0c8f86e40d..d9152c21bf 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -56,8 +56,8 @@ static void stuff_change(struct diff_options *opt,
 
 	one = alloc_filespec(old_path);
 	two = alloc_filespec(new_path);
-	fill_filespec(one, old_oid->hash, old_oid_valid, old_mode);
-	fill_filespec(two, new_oid->hash, new_oid_valid, new_mode);
+	fill_filespec(one, old_oid, old_oid_valid, old_mode);
+	fill_filespec(two, new_oid, new_oid_valid, new_mode);
 
 	diff_queue(&diff_queued_diff, one, two);
 }
@@ -174,7 +174,7 @@ static int builtin_diff_tree(struct rev_info *revs,
 		swap = 1;
 	oid[swap] = &ent0->item->oid;
 	oid[1 - swap] = &ent1->item->oid;
-	diff_tree_sha1(oid[0]->hash, oid[1]->hash, "", &revs->diffopt);
+	diff_tree_oid(oid[0], oid[1], "", &revs->diffopt);
 	log_tree_diff_flush(revs);
 	return 0;
 }
@@ -194,7 +194,7 @@ static int builtin_diff_combined(struct rev_info *revs,
 		revs->dense_combined_merges = revs->combine_merges = 1;
 	for (i = 1; i < ents; i++)
 		oid_array_append(&parents, &ent[i].item->oid);
-	diff_tree_combined(ent[0].item->oid.hash, &parents,
+	diff_tree_combined(&ent[0].item->oid, &parents,
 			   revs->dense_combined_merges, revs);
 	oid_array_clear(&parents);
 	return 0;
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 2dfed87454..a932be04f4 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -562,12 +562,12 @@ static void handle_commit(struct commit *commit, struct rev_info *rev)
 	    get_object_mark(&commit->parents->item->object) != 0 &&
 	    !full_tree) {
 		parse_commit_or_die(commit->parents->item);
-		diff_tree_sha1(commit->parents->item->tree->object.oid.hash,
-			       commit->tree->object.oid.hash, "", &rev->diffopt);
+		diff_tree_oid(&commit->parents->item->tree->object.oid,
+			      &commit->tree->object.oid, "", &rev->diffopt);
 	}
 	else
-		diff_root_tree_sha1(commit->tree->object.oid.hash,
-				    "", &rev->diffopt);
+		diff_root_tree_oid(&commit->tree->object.oid,
+				   "", &rev->diffopt);
 
 	/* Export the referenced blobs, and remember the marks. */
 	for (i = 0; i < diff_queued_diff.nr; i++)
diff --git a/builtin/grep.c b/builtin/grep.c
index 26d43b4e4c..3e4b9600e8 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -342,7 +342,7 @@ static int grep_oid(struct grep_opt *opt, const struct object_id *oid,
 
 #ifndef NO_PTHREADS
 	if (num_threads) {
-		add_work(opt, GREP_SOURCE_SHA1, pathbuf.buf, path, oid);
+		add_work(opt, GREP_SOURCE_OID, pathbuf.buf, path, oid);
 		strbuf_release(&pathbuf);
 		return 0;
 	} else
@@ -351,7 +351,7 @@ static int grep_oid(struct grep_opt *opt, const struct object_id *oid,
 		struct grep_source gs;
 		int hit;
 
-		grep_source_init(&gs, GREP_SOURCE_SHA1, pathbuf.buf, path, oid);
+		grep_source_init(&gs, GREP_SOURCE_OID, pathbuf.buf, path, oid);
 		strbuf_release(&pathbuf);
 		hit = grep_source(opt, &gs);
 
@@ -587,7 +587,7 @@ static int grep_submodule_launch(struct grep_opt *opt,
 	 * with the object's name: 'tree-name:filename'.  In order to
 	 * provide uniformity of output we want to pass the name of the
 	 * parent project's object name to the submodule so the submodule can
-	 * prefix its output with the parent's name and not its own SHA1.
+	 * prefix its output with the parent's name and not its own OID.
 	 */
 	if (gs->identifier && end_of_base)
 		argv_array_pushf(&cp.args, "--parent-basename=%.*s",
@@ -600,12 +600,12 @@ static int grep_submodule_launch(struct grep_opt *opt,
 		 * If there is a tree identifier for the submodule, add the
 		 * rev after adding the submodule options but before the
 		 * pathspecs.  To do this we listen for the '--' and insert the
-		 * sha1 before pushing the '--' onto the child process argv
+		 * oid before pushing the '--' onto the child process argv
 		 * array.
 		 */
 		if (gs->identifier &&
 		    !strcmp("--", submodule_options.argv[i])) {
-			argv_array_push(&cp.args, sha1_to_hex(gs->identifier));
+			argv_array_push(&cp.args, oid_to_hex(gs->identifier));
 		}
 
 		argv_array_push(&cp.args, submodule_options.argv[i]);
@@ -635,11 +635,11 @@ static int grep_submodule_launch(struct grep_opt *opt,
 
 /*
  * Prep grep structures for a submodule grep
- * sha1: the sha1 of the submodule or NULL if using the working tree
+ * oid: the oid of the submodule or NULL if using the working tree
  * filename: name of the submodule including tree name of parent
  * path: location of the submodule
  */
-static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
+static int grep_submodule(struct grep_opt *opt, const struct object_id *oid,
 			  const char *filename, const char *path)
 {
 	if (!is_submodule_initialized(path))
@@ -649,7 +649,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 		 * If searching history, check for the presense of the
 		 * submodule's gitdir before skipping the submodule.
 		 */
-		if (sha1) {
+		if (oid) {
 			const struct submodule *sub =
 					submodule_from_path(null_sha1, path);
 			if (sub)
@@ -664,7 +664,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 
 #ifndef NO_PTHREADS
 	if (num_threads) {
-		add_work(opt, GREP_SOURCE_SUBMODULE, filename, path, sha1);
+		add_work(opt, GREP_SOURCE_SUBMODULE, filename, path, oid);
 		return 0;
 	} else
 #endif
@@ -673,7 +673,7 @@ static int grep_submodule(struct grep_opt *opt, const unsigned char *sha1,
 		int hit;
 
 		grep_source_init(&gs, GREP_SOURCE_SUBMODULE,
-				 filename, path, sha1);
+				 filename, path, oid);
 		hit = grep_submodule_launch(opt, &gs);
 
 		grep_source_clear(&gs);
@@ -792,7 +792,7 @@ static int grep_tree(struct grep_opt *opt, const struct pathspec *pathspec,
 					 check_attr);
 			free(data);
 		} else if (recurse_submodules && S_ISGITLINK(entry.mode)) {
-			hit |= grep_submodule(opt, entry.oid->hash, base->buf,
+			hit |= grep_submodule(opt, entry.oid, base->buf,
 					      base->buf + tn_len);
 		}
 
diff --git a/builtin/log.c b/builtin/log.c
index a33c1a70ab..998437b23d 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1052,9 +1052,9 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 
 	diff_setup_done(&opts);
 
-	diff_tree_sha1(origin->tree->object.oid.hash,
-		       head->tree->object.oid.hash,
-		       "", &opts);
+	diff_tree_oid(&origin->tree->object.oid,
+		      &head->tree->object.oid,
+		      "", &opts);
 	diffcore_std(&opts);
 	diff_flush(&opts);
 
@@ -1363,7 +1363,7 @@ static void prepare_bases(struct base_tree_info *bases,
 		struct object_id *patch_id;
 		if (commit->util)
 			continue;
-		if (commit_patch_id(commit, &diffopt, oid.hash, 0))
+		if (commit_patch_id(commit, &diffopt, &oid, 0))
 			die(_("cannot get patch id"));
 		ALLOC_GROW(bases->patch_id, bases->nr_patch_id + 1, bases->alloc_patch_id);
 		patch_id = bases->patch_id + bases->nr_patch_id;
diff --git a/builtin/merge.c b/builtin/merge.c
index eab03a026d..84970cd85e 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -415,7 +415,7 @@ static void finish(struct commit *head_commit,
 			DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 		opts.detect_rename = DIFF_DETECT_RENAME;
 		diff_setup_done(&opts);
-		diff_tree_sha1(head->hash, new_head->hash, "", &opts);
+		diff_tree_oid(head, new_head, "", &opts);
 		diffcore_std(&opts);
 		diff_flush(&opts);
 	}
diff --git a/builtin/notes.c b/builtin/notes.c
index 7196bff0eb..c939a84b76 100644
--- a/builtin/notes.c
+++ b/builtin/notes.c
@@ -109,11 +109,11 @@ static void free_note_data(struct note_data *d)
 	strbuf_release(&d->buf);
 }
 
-static int list_each_note(const unsigned char *object_sha1,
-		const unsigned char *note_sha1, char *note_path,
+static int list_each_note(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
 		void *cb_data)
 {
-	printf("%s %s\n", sha1_to_hex(note_sha1), sha1_to_hex(object_sha1));
+	printf("%s %s\n", oid_to_hex(note_oid), oid_to_hex(object_oid));
 	return 0;
 }
 
@@ -129,10 +129,10 @@ static void copy_obj_to_fd(int fd, const unsigned char *sha1)
 	}
 }
 
-static void write_commented_object(int fd, const unsigned char *object)
+static void write_commented_object(int fd, const struct object_id *object)
 {
 	const char *show_args[5] =
-		{"show", "--stat", "--no-notes", sha1_to_hex(object), NULL};
+		{"show", "--stat", "--no-notes", oid_to_hex(object), NULL};
 	struct child_process show = CHILD_PROCESS_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf cbuf = STRBUF_INIT;
@@ -145,7 +145,7 @@ static void write_commented_object(int fd, const unsigned char *object)
 	show.git_cmd = 1;
 	if (start_command(&show))
 		die(_("unable to start 'show' for object '%s'"),
-		    sha1_to_hex(object));
+		    oid_to_hex(object));
 
 	if (strbuf_read(&buf, show.out, 0) < 0)
 		die_errno(_("could not read 'show' output"));
@@ -157,10 +157,10 @@ static void write_commented_object(int fd, const unsigned char *object)
 
 	if (finish_command(&show))
 		die(_("failed to finish 'show' for object '%s'"),
-		    sha1_to_hex(object));
+		    oid_to_hex(object));
 }
 
-static void prepare_note_data(const unsigned char *object, struct note_data *d,
+static void prepare_note_data(const struct object_id *object, struct note_data *d,
 		const unsigned char *old_note)
 {
 	if (d->use_editor || !d->given) {
@@ -243,16 +243,16 @@ static int parse_reuse_arg(const struct option *opt, const char *arg, int unset)
 {
 	struct note_data *d = opt->value;
 	char *buf;
-	unsigned char object[20];
+	struct object_id object;
 	enum object_type type;
 	unsigned long len;
 
 	if (d->buf.len)
 		strbuf_addch(&d->buf, '\n');
 
-	if (get_sha1(arg, object))
+	if (get_oid(arg, &object))
 		die(_("failed to resolve '%s' as a valid ref."), arg);
-	if (!(buf = read_sha1_file(object, &type, &len))) {
+	if (!(buf = read_sha1_file(object.hash, &type, &len))) {
 		free(buf);
 		die(_("failed to read object '%s'."), arg);
 	}
@@ -292,7 +292,7 @@ static int notes_copy_from_stdin(int force, const char *rewrite_cmd)
 	}
 
 	while (strbuf_getline_lf(&buf, stdin) != EOF) {
-		unsigned char from_obj[20], to_obj[20];
+		struct object_id from_obj, to_obj;
 		struct strbuf **split;
 		int err;
 
@@ -301,15 +301,15 @@ static int notes_copy_from_stdin(int force, const char *rewrite_cmd)
 			die(_("malformed input line: '%s'."), buf.buf);
 		strbuf_rtrim(split[0]);
 		strbuf_rtrim(split[1]);
-		if (get_sha1(split[0]->buf, from_obj))
+		if (get_oid(split[0]->buf, &from_obj))
 			die(_("failed to resolve '%s' as a valid ref."), split[0]->buf);
-		if (get_sha1(split[1]->buf, to_obj))
+		if (get_oid(split[1]->buf, &to_obj))
 			die(_("failed to resolve '%s' as a valid ref."), split[1]->buf);
 
 		if (rewrite_cmd)
-			err = copy_note_for_rewrite(c, from_obj, to_obj);
+			err = copy_note_for_rewrite(c, &from_obj, &to_obj);
 		else
-			err = copy_note(t, from_obj, to_obj, force,
+			err = copy_note(t, &from_obj, &to_obj, force,
 					combine_notes_overwrite);
 
 		if (err) {
@@ -352,8 +352,8 @@ static struct notes_tree *init_notes_check(const char *subcommand,
 static int list(int argc, const char **argv, const char *prefix)
 {
 	struct notes_tree *t;
-	unsigned char object[20];
-	const unsigned char *note;
+	struct object_id object;
+	const struct object_id *note;
 	int retval = -1;
 	struct option options[] = {
 		OPT_END()
@@ -370,15 +370,15 @@ static int list(int argc, const char **argv, const char *prefix)
 
 	t = init_notes_check("list", 0);
 	if (argc) {
-		if (get_sha1(argv[0], object))
+		if (get_oid(argv[0], &object))
 			die(_("failed to resolve '%s' as a valid ref."), argv[0]);
-		note = get_note(t, object);
+		note = get_note(t, &object);
 		if (note) {
-			puts(sha1_to_hex(note));
+			puts(oid_to_hex(note));
 			retval = 0;
 		} else
 			retval = error(_("no note found for object %s."),
-				       sha1_to_hex(object));
+				       oid_to_hex(&object));
 	} else
 		retval = for_each_note(t, 0, list_each_note, NULL);
 
@@ -393,8 +393,8 @@ static int add(int argc, const char **argv, const char *prefix)
 	int force = 0, allow_empty = 0;
 	const char *object_ref;
 	struct notes_tree *t;
-	unsigned char object[20], new_note[20];
-	const unsigned char *note;
+	struct object_id object, new_note;
+	const struct object_id *note;
 	struct note_data d = { 0, 0, NULL, STRBUF_INIT };
 	struct option options[] = {
 		{ OPTION_CALLBACK, 'm', "message", &d, N_("message"),
@@ -425,11 +425,11 @@ static int add(int argc, const char **argv, const char *prefix)
 
 	object_ref = argc > 1 ? argv[1] : "HEAD";
 
-	if (get_sha1(object_ref, object))
+	if (get_oid(object_ref, &object))
 		die(_("failed to resolve '%s' as a valid ref."), object_ref);
 
 	t = init_notes_check("add", NOTES_INIT_WRITABLE);
-	note = get_note(t, object);
+	note = get_note(t, &object);
 
 	if (note) {
 		if (!force) {
@@ -439,7 +439,7 @@ static int add(int argc, const char **argv, const char *prefix)
 				return error(_("Cannot add notes. "
 					"Found existing notes for object %s. "
 					"Use '-f' to overwrite existing notes"),
-					sha1_to_hex(object));
+					oid_to_hex(&object));
 			}
 			/*
 			 * Redirect to "edit" subcommand.
@@ -452,19 +452,19 @@ static int add(int argc, const char **argv, const char *prefix)
 			return append_edit(argc, argv, prefix);
 		}
 		fprintf(stderr, _("Overwriting existing notes for object %s\n"),
-			sha1_to_hex(object));
+			oid_to_hex(&object));
 	}
 
-	prepare_note_data(object, &d, note);
+	prepare_note_data(&object, &d, note->hash);
 	if (d.buf.len || allow_empty) {
-		write_note_data(&d, new_note);
-		if (add_note(t, object, new_note, combine_notes_overwrite))
+		write_note_data(&d, new_note.hash);
+		if (add_note(t, &object, &new_note, combine_notes_overwrite))
 			die("BUG: combine_notes_overwrite failed");
 		commit_notes(t, "Notes added by 'git notes add'");
 	} else {
 		fprintf(stderr, _("Removing note for object %s\n"),
-			sha1_to_hex(object));
-		remove_note(t, object);
+			oid_to_hex(&object));
+		remove_note(t, object.hash);
 		commit_notes(t, "Notes removed by 'git notes add'");
 	}
 
@@ -476,9 +476,9 @@ static int add(int argc, const char **argv, const char *prefix)
 static int copy(int argc, const char **argv, const char *prefix)
 {
 	int retval = 0, force = 0, from_stdin = 0;
-	const unsigned char *from_note, *note;
+	const struct object_id *from_note, *note;
 	const char *object_ref;
-	unsigned char object[20], from_obj[20];
+	struct object_id object, from_obj;
 	struct notes_tree *t;
 	const char *rewrite_cmd = NULL;
 	struct option options[] = {
@@ -511,37 +511,37 @@ static int copy(int argc, const char **argv, const char *prefix)
 		usage_with_options(git_notes_copy_usage, options);
 	}
 
-	if (get_sha1(argv[0], from_obj))
+	if (get_oid(argv[0], &from_obj))
 		die(_("failed to resolve '%s' as a valid ref."), argv[0]);
 
 	object_ref = 1 < argc ? argv[1] : "HEAD";
 
-	if (get_sha1(object_ref, object))
+	if (get_oid(object_ref, &object))
 		die(_("failed to resolve '%s' as a valid ref."), object_ref);
 
 	t = init_notes_check("copy", NOTES_INIT_WRITABLE);
-	note = get_note(t, object);
+	note = get_note(t, &object);
 
 	if (note) {
 		if (!force) {
 			retval = error(_("Cannot copy notes. Found existing "
 				       "notes for object %s. Use '-f' to "
 				       "overwrite existing notes"),
-				       sha1_to_hex(object));
+				       oid_to_hex(&object));
 			goto out;
 		}
 		fprintf(stderr, _("Overwriting existing notes for object %s\n"),
-			sha1_to_hex(object));
+			oid_to_hex(&object));
 	}
 
-	from_note = get_note(t, from_obj);
+	from_note = get_note(t, &from_obj);
 	if (!from_note) {
 		retval = error(_("missing notes on source object %s. Cannot "
-			       "copy."), sha1_to_hex(from_obj));
+			       "copy."), oid_to_hex(&from_obj));
 		goto out;
 	}
 
-	if (add_note(t, object, from_note, combine_notes_overwrite))
+	if (add_note(t, &object, from_note, combine_notes_overwrite))
 		die("BUG: combine_notes_overwrite failed");
 	commit_notes(t, "Notes added by 'git notes copy'");
 out:
@@ -554,8 +554,8 @@ static int append_edit(int argc, const char **argv, const char *prefix)
 	int allow_empty = 0;
 	const char *object_ref;
 	struct notes_tree *t;
-	unsigned char object[20], new_note[20];
-	const unsigned char *note;
+	struct object_id object, new_note;
+	const struct object_id *note;
 	char *logmsg;
 	const char * const *usage;
 	struct note_data d = { 0, 0, NULL, STRBUF_INIT };
@@ -594,19 +594,19 @@ static int append_edit(int argc, const char **argv, const char *prefix)
 
 	object_ref = 1 < argc ? argv[1] : "HEAD";
 
-	if (get_sha1(object_ref, object))
+	if (get_oid(object_ref, &object))
 		die(_("failed to resolve '%s' as a valid ref."), object_ref);
 
 	t = init_notes_check(argv[0], NOTES_INIT_WRITABLE);
-	note = get_note(t, object);
+	note = get_note(t, &object);
 
-	prepare_note_data(object, &d, edit ? note : NULL);
+	prepare_note_data(&object, &d, edit && note ? note->hash : NULL);
 
 	if (note && !edit) {
 		/* Append buf to previous note contents */
 		unsigned long size;
 		enum object_type type;
-		char *prev_buf = read_sha1_file(note, &type, &size);
+		char *prev_buf = read_sha1_file(note->hash, &type, &size);
 
 		strbuf_grow(&d.buf, size + 1);
 		if (d.buf.len && prev_buf && size)
@@ -617,14 +617,14 @@ static int append_edit(int argc, const char **argv, const char *prefix)
 	}
 
 	if (d.buf.len || allow_empty) {
-		write_note_data(&d, new_note);
-		if (add_note(t, object, new_note, combine_notes_overwrite))
+		write_note_data(&d, new_note.hash);
+		if (add_note(t, &object, &new_note, combine_notes_overwrite))
 			die("BUG: combine_notes_overwrite failed");
 		logmsg = xstrfmt("Notes added by 'git notes %s'", argv[0]);
 	} else {
 		fprintf(stderr, _("Removing note for object %s\n"),
-			sha1_to_hex(object));
-		remove_note(t, object);
+			oid_to_hex(&object));
+		remove_note(t, object.hash);
 		logmsg = xstrfmt("Notes removed by 'git notes %s'", argv[0]);
 	}
 	commit_notes(t, logmsg);
@@ -639,8 +639,8 @@ static int show(int argc, const char **argv, const char *prefix)
 {
 	const char *object_ref;
 	struct notes_tree *t;
-	unsigned char object[20];
-	const unsigned char *note;
+	struct object_id object;
+	const struct object_id *note;
 	int retval;
 	struct option options[] = {
 		OPT_END()
@@ -656,17 +656,17 @@ static int show(int argc, const char **argv, const char *prefix)
 
 	object_ref = argc ? argv[0] : "HEAD";
 
-	if (get_sha1(object_ref, object))
+	if (get_oid(object_ref, &object))
 		die(_("failed to resolve '%s' as a valid ref."), object_ref);
 
 	t = init_notes_check("show", 0);
-	note = get_note(t, object);
+	note = get_note(t, &object);
 
 	if (!note)
 		retval = error(_("no note found for object %s."),
-			       sha1_to_hex(object));
+			       oid_to_hex(&object));
 	else {
-		const char *show_args[3] = {"show", sha1_to_hex(note), NULL};
+		const char *show_args[3] = {"show", oid_to_hex(note), NULL};
 		retval = execv_git_cmd(show_args);
 	}
 	free_notes(t);
@@ -726,7 +726,7 @@ static int merge_commit(struct notes_merge_options *o)
 	if (!o->local_ref)
 		die(_("failed to resolve NOTES_MERGE_REF"));
 
-	if (notes_merge_commit(o, t, partial, oid.hash))
+	if (notes_merge_commit(o, t, partial, &oid))
 		die(_("failed to finalize notes merge"));
 
 	/* Reuse existing commit message in reflog message */
@@ -762,7 +762,7 @@ static int git_config_get_notes_strategy(const char *key,
 static int merge(int argc, const char **argv, const char *prefix)
 {
 	struct strbuf remote_ref = STRBUF_INIT, msg = STRBUF_INIT;
-	unsigned char result_sha1[20];
+	struct object_id result_oid;
 	struct notes_tree *t;
 	struct notes_merge_options o;
 	int do_merge = 0, do_commit = 0, do_abort = 0;
@@ -844,16 +844,16 @@ static int merge(int argc, const char **argv, const char *prefix)
 		    remote_ref.buf, default_notes_ref());
 	strbuf_add(&(o.commit_msg), msg.buf + 7, msg.len - 7); /* skip "notes: " */
 
-	result = notes_merge(&o, t, result_sha1);
+	result = notes_merge(&o, t, &result_oid);
 
-	if (result >= 0) /* Merge resulted (trivially) in result_sha1 */
+	if (result >= 0) /* Merge resulted (trivially) in result_oid */
 		/* Update default notes ref with new commit */
-		update_ref(msg.buf, default_notes_ref(), result_sha1, NULL,
+		update_ref(msg.buf, default_notes_ref(), result_oid.hash, NULL,
 			   0, UPDATE_REFS_DIE_ON_ERR);
 	else { /* Merge has unresolved conflicts */
 		const struct worktree *wt;
 		/* Update .git/NOTES_MERGE_PARTIAL with partial merge result */
-		update_ref(msg.buf, "NOTES_MERGE_PARTIAL", result_sha1, NULL,
+		update_ref(msg.buf, "NOTES_MERGE_PARTIAL", result_oid.hash, NULL,
 			   0, UPDATE_REFS_DIE_ON_ERR);
 		/* Store ref-to-be-updated into .git/NOTES_MERGE_REF */
 		wt = find_shared_symref("NOTES_MERGE_REF", default_notes_ref());
@@ -880,10 +880,10 @@ static int merge(int argc, const char **argv, const char *prefix)
 static int remove_one_note(struct notes_tree *t, const char *name, unsigned flag)
 {
 	int status;
-	unsigned char sha1[20];
-	if (get_sha1(name, sha1))
+	struct object_id oid;
+	if (get_oid(name, &oid))
 		return error(_("Failed to resolve '%s' as a valid ref."), name);
-	status = remove_note(t, sha1);
+	status = remove_note(t, oid.hash);
 	if (status)
 		fprintf(stderr, _("Object %s has no note\n"), name);
 	else
diff --git a/cache.h b/cache.h
index 4d92aae0e8..d6ba8a2f11 100644
--- a/cache.h
+++ b/cache.h
@@ -1026,6 +1026,13 @@ static inline void oidcpy(struct object_id *dst, const struct object_id *src)
 	hashcpy(dst->hash, src->hash);
 }
 
+static inline struct object_id *oiddup(const struct object_id *src)
+{
+	struct object_id *dst = xmalloc(sizeof(struct object_id));
+	oidcpy(dst, src);
+	return dst;
+}
+
 static inline void hashclr(unsigned char *hash)
 {
 	memset(hash, 0, GIT_SHA1_RAWSZ);
diff --git a/combine-diff.c b/combine-diff.c
index 2848034fe9..ec9d930440 100644
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -302,7 +302,7 @@ static char *grab_blob(const struct object_id *oid, unsigned int mode,
 		return xcalloc(1, 1);
 	} else if (textconv) {
 		struct diff_filespec *df = alloc_filespec(path);
-		fill_filespec(df, oid->hash, 1, mode);
+		fill_filespec(df, oid, 1, mode);
 		*size = fill_textconv(textconv, df, &blob);
 		free_filespec(df);
 	} else {
@@ -1022,7 +1022,7 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 						   &result_size, NULL, NULL);
 		} else if (textconv) {
 			struct diff_filespec *df = alloc_filespec(elem->path);
-			fill_filespec(df, null_sha1, 0, st.st_mode);
+			fill_filespec(df, &null_oid, 0, st.st_mode);
 			result_size = fill_textconv(textconv, df, &result);
 			free_filespec(df);
 		} else if (0 <= (fd = open(elem->path, O_RDONLY))) {
@@ -1311,7 +1311,7 @@ static const char *path_path(void *obj)
 
 
 /* find set of paths that every parent touches */
-static struct combine_diff_path *find_paths_generic(const unsigned char *sha1,
+static struct combine_diff_path *find_paths_generic(const struct object_id *oid,
 	const struct oid_array *parents, struct diff_options *opt)
 {
 	struct combine_diff_path *paths = NULL;
@@ -1336,7 +1336,7 @@ static struct combine_diff_path *find_paths_generic(const unsigned char *sha1,
 			opt->output_format = stat_opt;
 		else
 			opt->output_format = DIFF_FORMAT_NO_OUTPUT;
-		diff_tree_sha1(parents->oid[i].hash, sha1, "", opt);
+		diff_tree_oid(&parents->oid[i], oid, "", opt);
 		diffcore_std(opt);
 		paths = intersect_paths(paths, i, num_parent);
 
@@ -1360,31 +1360,31 @@ static struct combine_diff_path *find_paths_generic(const unsigned char *sha1,
  * rename/copy detection, etc, comparing all trees simultaneously (= faster).
  */
 static struct combine_diff_path *find_paths_multitree(
-	const unsigned char *sha1, const struct oid_array *parents,
+	const struct object_id *oid, const struct oid_array *parents,
 	struct diff_options *opt)
 {
 	int i, nparent = parents->nr;
-	const unsigned char **parents_sha1;
+	const struct object_id **parents_oid;
 	struct combine_diff_path paths_head;
 	struct strbuf base;
 
-	ALLOC_ARRAY(parents_sha1, nparent);
+	ALLOC_ARRAY(parents_oid, nparent);
 	for (i = 0; i < nparent; i++)
-		parents_sha1[i] = parents->oid[i].hash;
+		parents_oid[i] = &parents->oid[i];
 
 	/* fake list head, so worker can assume it is non-NULL */
 	paths_head.next = NULL;
 
 	strbuf_init(&base, PATH_MAX);
-	diff_tree_paths(&paths_head, sha1, parents_sha1, nparent, &base, opt);
+	diff_tree_paths(&paths_head, oid, parents_oid, nparent, &base, opt);
 
 	strbuf_release(&base);
-	free(parents_sha1);
+	free(parents_oid);
 	return paths_head.next;
 }
 
 
-void diff_tree_combined(const unsigned char *sha1,
+void diff_tree_combined(const struct object_id *oid,
 			const struct oid_array *parents,
 			int dense,
 			struct rev_info *rev)
@@ -1448,11 +1448,11 @@ void diff_tree_combined(const unsigned char *sha1,
 		 * diff(sha1,parent_i) for all i to do the job, specifically
 		 * for parent0.
 		 */
-		paths = find_paths_generic(sha1, parents, &diffopts);
+		paths = find_paths_generic(oid, parents, &diffopts);
 	}
 	else {
 		int stat_opt;
-		paths = find_paths_multitree(sha1, parents, &diffopts);
+		paths = find_paths_multitree(oid, parents, &diffopts);
 
 		/*
 		 * show stat against the first parent even
@@ -1463,7 +1463,7 @@ void diff_tree_combined(const unsigned char *sha1,
 		if (stat_opt) {
 			diffopts.output_format = stat_opt;
 
-			diff_tree_sha1(parents->oid[0].hash, sha1, "", &diffopts);
+			diff_tree_oid(&parents->oid[0], oid, "", &diffopts);
 			diffcore_std(&diffopts);
 			if (opt->orderfile)
 				diffcore_order(opt->orderfile);
@@ -1539,6 +1539,6 @@ void diff_tree_combined_merge(const struct commit *commit, int dense,
 		oid_array_append(&parents, &parent->item->object.oid);
 		parent = parent->next;
 	}
-	diff_tree_combined(commit->object.oid.hash, &parents, dense, rev);
+	diff_tree_combined(&commit->object.oid, &parents, dense, rev);
 	oid_array_clear(&parents);
 }
diff --git a/diff-lib.c b/diff-lib.c
index 76c8f185cd..0c0e20f7c0 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -101,7 +101,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 		struct cache_entry *ce = active_cache[i];
 		int changed;
 		unsigned dirty_submodule = 0;
-		const unsigned char *old_sha1, *new_sha1;
+		const struct object_id *old_oid, *new_oid;
 
 		if (diff_can_quit_early(&revs->diffopt))
 			break;
@@ -210,14 +210,14 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 					continue;
 				}
 				diff_addremove(&revs->diffopt, '-', ce->ce_mode,
-					       ce->oid.hash,
+					       &ce->oid,
 					       !is_null_oid(&ce->oid),
 					       ce->name, 0);
 				continue;
 			} else if (revs->diffopt.ita_invisible_in_index &&
 				   ce_intent_to_add(ce)) {
 				diff_addremove(&revs->diffopt, '+', ce->ce_mode,
-					       EMPTY_BLOB_SHA1_BIN, 0,
+					       &empty_tree_oid, 0,
 					       ce->name, 0);
 				continue;
 			}
@@ -233,12 +233,12 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 				continue;
 		}
 		oldmode = ce->ce_mode;
-		old_sha1 = ce->oid.hash;
-		new_sha1 = changed ? null_sha1 : ce->oid.hash;
+		old_oid = &ce->oid;
+		new_oid = changed ? &null_oid : &ce->oid;
 		diff_change(&revs->diffopt, oldmode, newmode,
-			    old_sha1, new_sha1,
-			    !is_null_sha1(old_sha1),
-			    !is_null_sha1(new_sha1),
+			    old_oid, new_oid,
+			    !is_null_oid(old_oid),
+			    !is_null_oid(new_oid),
 			    ce->name, 0, dirty_submodule);
 
 	}
@@ -255,21 +255,21 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 static void diff_index_show_file(struct rev_info *revs,
 				 const char *prefix,
 				 const struct cache_entry *ce,
-				 const unsigned char *sha1, int sha1_valid,
+				 const struct object_id *oid, int oid_valid,
 				 unsigned int mode,
 				 unsigned dirty_submodule)
 {
 	diff_addremove(&revs->diffopt, prefix[0], mode,
-		       sha1, sha1_valid, ce->name, dirty_submodule);
+		       oid, oid_valid, ce->name, dirty_submodule);
 }
 
 static int get_stat_data(const struct cache_entry *ce,
-			 const unsigned char **sha1p,
+			 const struct object_id **oidp,
 			 unsigned int *modep,
 			 int cached, int match_missing,
 			 unsigned *dirty_submodule, struct diff_options *diffopt)
 {
-	const unsigned char *sha1 = ce->oid.hash;
+	const struct object_id *oid = &ce->oid;
 	unsigned int mode = ce->ce_mode;
 
 	if (!cached && !ce_uptodate(ce)) {
@@ -280,7 +280,7 @@ static int get_stat_data(const struct cache_entry *ce,
 			return -1;
 		else if (changed) {
 			if (match_missing) {
-				*sha1p = sha1;
+				*oidp = oid;
 				*modep = mode;
 				return 0;
 			}
@@ -290,11 +290,11 @@ static int get_stat_data(const struct cache_entry *ce,
 						    0, dirty_submodule);
 		if (changed) {
 			mode = ce_mode_from_stat(ce, st.st_mode);
-			sha1 = null_sha1;
+			oid = &null_oid;
 		}
 	}
 
-	*sha1p = sha1;
+	*oidp = oid;
 	*modep = mode;
 	return 0;
 }
@@ -303,7 +303,7 @@ static void show_new_file(struct rev_info *revs,
 			  const struct cache_entry *new,
 			  int cached, int match_missing)
 {
-	const unsigned char *sha1;
+	const struct object_id *oid;
 	unsigned int mode;
 	unsigned dirty_submodule = 0;
 
@@ -311,11 +311,11 @@ static void show_new_file(struct rev_info *revs,
 	 * New file in the index: it might actually be different in
 	 * the working tree.
 	 */
-	if (get_stat_data(new, &sha1, &mode, cached, match_missing,
+	if (get_stat_data(new, &oid, &mode, cached, match_missing,
 	    &dirty_submodule, &revs->diffopt) < 0)
 		return;
 
-	diff_index_show_file(revs, "+", new, sha1, !is_null_sha1(sha1), mode, dirty_submodule);
+	diff_index_show_file(revs, "+", new, oid, !is_null_oid(oid), mode, dirty_submodule);
 }
 
 static int show_modified(struct rev_info *revs,
@@ -325,20 +325,20 @@ static int show_modified(struct rev_info *revs,
 			 int cached, int match_missing)
 {
 	unsigned int mode, oldmode;
-	const unsigned char *sha1;
+	const struct object_id *oid;
 	unsigned dirty_submodule = 0;
 
-	if (get_stat_data(new, &sha1, &mode, cached, match_missing,
+	if (get_stat_data(new, &oid, &mode, cached, match_missing,
 			  &dirty_submodule, &revs->diffopt) < 0) {
 		if (report_missing)
 			diff_index_show_file(revs, "-", old,
-					     old->oid.hash, 1, old->ce_mode,
+					     &old->oid, 1, old->ce_mode,
 					     0);
 		return -1;
 	}
 
 	if (revs->combine_merges && !cached &&
-	    (hashcmp(sha1, old->oid.hash) || oidcmp(&old->oid, &new->oid))) {
+	    (oidcmp(oid, &old->oid) || oidcmp(&old->oid, &new->oid))) {
 		struct combine_diff_path *p;
 		int pathlen = ce_namelen(new);
 
@@ -362,12 +362,12 @@ static int show_modified(struct rev_info *revs,
 	}
 
 	oldmode = old->ce_mode;
-	if (mode == oldmode && !hashcmp(sha1, old->oid.hash) && !dirty_submodule &&
+	if (mode == oldmode && !oidcmp(oid, &old->oid) && !dirty_submodule &&
 	    !DIFF_OPT_TST(&revs->diffopt, FIND_COPIES_HARDER))
 		return 0;
 
 	diff_change(&revs->diffopt, oldmode, mode,
-		    old->oid.hash, sha1, 1, !is_null_sha1(sha1),
+		    &old->oid, oid, 1, !is_null_oid(oid),
 		    old->name, 0, dirty_submodule);
 	return 0;
 }
@@ -409,7 +409,7 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 		struct diff_filepair *pair;
 		pair = diff_unmerge(&revs->diffopt, idx->name);
 		if (tree)
-			fill_filespec(pair->one, tree->oid.hash, 1,
+			fill_filespec(pair->one, &tree->oid, 1,
 				      tree->ce_mode);
 		return;
 	}
@@ -426,7 +426,7 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 	 * Something removed from the tree?
 	 */
 	if (!idx) {
-		diff_index_show_file(revs, "-", tree, tree->oid.hash, 1,
+		diff_index_show_file(revs, "-", tree, &tree->oid, 1,
 				     tree->ce_mode, 0);
 		return;
 	}
diff --git a/diff-no-index.c b/diff-no-index.c
index 79229382b0..80ff17d460 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -82,7 +82,7 @@ static struct diff_filespec *noindex_filespec(const char *name, int mode)
 	if (!name)
 		name = "/dev/null";
 	s = alloc_filespec(name);
-	fill_filespec(s, null_sha1, 0, mode);
+	fill_filespec(s, &null_oid, 0, mode);
 	if (name == file_from_standard_input)
 		populate_from_stdin(s);
 	return s;
diff --git a/diff.c b/diff.c
index e35cf6c704..acedf86aec 100644
--- a/diff.c
+++ b/diff.c
@@ -2702,13 +2702,13 @@ void free_filespec(struct diff_filespec *spec)
 	}
 }
 
-void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
-		   int sha1_valid, unsigned short mode)
+void fill_filespec(struct diff_filespec *spec, const struct object_id *oid,
+		   int oid_valid, unsigned short mode)
 {
 	if (mode) {
 		spec->mode = canon_mode(mode);
-		hashcpy(spec->oid.hash, sha1);
-		spec->oid_valid = sha1_valid;
+		oidcpy(&spec->oid, oid);
+		spec->oid_valid = oid_valid;
 	}
 }
 
@@ -2717,7 +2717,7 @@ void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
  * the work tree has that object contents, return true, so that
  * prepare_temp_file() does not have to inflate and extract.
  */
-static int reuse_worktree_file(const char *name, const unsigned char *sha1, int want_file)
+static int reuse_worktree_file(const char *name, const struct object_id *oid, int want_file)
 {
 	const struct cache_entry *ce;
 	struct stat st;
@@ -2748,7 +2748,7 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int
 	 * objects however would tend to be slower as they need
 	 * to be individually opened and inflated.
 	 */
-	if (!FAST_WORKING_DIRECTORY && !want_file && has_sha1_pack(sha1))
+	if (!FAST_WORKING_DIRECTORY && !want_file && has_sha1_pack(oid->hash))
 		return 0;
 
 	/*
@@ -2768,7 +2768,7 @@ static int reuse_worktree_file(const char *name, const unsigned char *sha1, int
 	 * This is not the sha1 we are looking for, or
 	 * unreusable because it is not a regular file.
 	 */
-	if (hashcmp(sha1, ce->oid.hash) || !S_ISREG(ce->ce_mode))
+	if (oidcmp(oid, &ce->oid) || !S_ISREG(ce->ce_mode))
 		return 0;
 
 	/*
@@ -2842,7 +2842,7 @@ int diff_populate_filespec(struct diff_filespec *s, unsigned int flags)
 		return diff_populate_gitlink(s, size_only);
 
 	if (!s->oid_valid ||
-	    reuse_worktree_file(s->path, s->oid.hash, 0)) {
+	    reuse_worktree_file(s->path, &s->oid, 0)) {
 		struct strbuf buf = STRBUF_INIT;
 		struct stat st;
 		int fd;
@@ -3008,7 +3008,7 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
 
 	if (!S_ISGITLINK(one->mode) &&
 	    (!one->oid_valid ||
-	     reuse_worktree_file(name, one->oid.hash, 1))) {
+	     reuse_worktree_file(name, &one->oid, 1))) {
 		struct stat st;
 		if (lstat(name, &st) < 0) {
 			if (errno == ENOENT)
@@ -3030,13 +3030,13 @@ static struct diff_tempfile *prepare_temp_file(const char *name,
 			/* we can borrow from the file in the work tree */
 			temp->name = name;
 			if (!one->oid_valid)
-				sha1_to_hex_r(temp->hex, null_sha1);
+				oid_to_hex_r(temp->hex, &null_oid);
 			else
 				oid_to_hex_r(temp->hex, &one->oid);
 			/* Even though we may sometimes borrow the
 			 * contents from the work tree, we always want
 			 * one->mode.  mode is trustworthy even when
-			 * !(one->sha1_valid), as long as
+			 * !(one->oid_valid), as long as
 			 * DIFF_FILE_VALID(one).
 			 */
 			xsnprintf(temp->mode, sizeof(temp->mode), "%06o", one->mode);
@@ -3239,7 +3239,7 @@ static void run_diff_cmd(const char *pgm,
 		fprintf(o->file, "* Unmerged path %s\n", name);
 }
 
-static void diff_fill_sha1_info(struct diff_filespec *one)
+static void diff_fill_oid_info(struct diff_filespec *one)
 {
 	if (DIFF_FILE_VALID(one)) {
 		if (!one->oid_valid) {
@@ -3298,8 +3298,8 @@ static void run_diff(struct diff_filepair *p, struct diff_options *o)
 		return;
 	}
 
-	diff_fill_sha1_info(one);
-	diff_fill_sha1_info(two);
+	diff_fill_oid_info(one);
+	diff_fill_oid_info(two);
 
 	if (!pgm &&
 	    DIFF_FILE_VALID(one) && DIFF_FILE_VALID(two) &&
@@ -3344,8 +3344,8 @@ static void run_diffstat(struct diff_filepair *p, struct diff_options *o,
 	if (o->prefix_length)
 		strip_prefix(o->prefix_length, &name, &other);
 
-	diff_fill_sha1_info(p->one);
-	diff_fill_sha1_info(p->two);
+	diff_fill_oid_info(p->one);
+	diff_fill_oid_info(p->two);
 
 	builtin_diffstat(name, other, p->one, p->two, diffstat, o, p);
 }
@@ -3368,8 +3368,8 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 	if (o->prefix_length)
 		strip_prefix(o->prefix_length, &name, &other);
 
-	diff_fill_sha1_info(p->one);
-	diff_fill_sha1_info(p->two);
+	diff_fill_oid_info(p->one);
+	diff_fill_oid_info(p->two);
 
 	builtin_checkdiff(name, other, attr_path, p->one, p->two, o);
 }
@@ -4582,7 +4582,7 @@ static void patch_id_add_mode(git_SHA_CTX *ctx, unsigned mode)
 }
 
 /* returns 0 upon success, and writes result into sha1 */
-static int diff_get_patch_id(struct diff_options *options, unsigned char *sha1, int diff_header_only)
+static int diff_get_patch_id(struct diff_options *options, struct object_id *oid, int diff_header_only)
 {
 	struct diff_queue_struct *q = &diff_queued_diff;
 	int i;
@@ -4614,8 +4614,8 @@ static int diff_get_patch_id(struct diff_options *options, unsigned char *sha1,
 		if (DIFF_PAIR_UNMERGED(p))
 			continue;
 
-		diff_fill_sha1_info(p->one);
-		diff_fill_sha1_info(p->two);
+		diff_fill_oid_info(p->one);
+		diff_fill_oid_info(p->two);
 
 		len1 = remove_space(p->one->path, strlen(p->one->path));
 		len2 = remove_space(p->two->path, strlen(p->two->path));
@@ -4654,9 +4654,9 @@ static int diff_get_patch_id(struct diff_options *options, unsigned char *sha1,
 		if (diff_filespec_is_binary(p->one) ||
 		    diff_filespec_is_binary(p->two)) {
 			git_SHA1_Update(&ctx, oid_to_hex(&p->one->oid),
-					40);
+					GIT_SHA1_HEXSZ);
 			git_SHA1_Update(&ctx, oid_to_hex(&p->two->oid),
-					40);
+					GIT_SHA1_HEXSZ);
 			continue;
 		}
 
@@ -4669,15 +4669,15 @@ static int diff_get_patch_id(struct diff_options *options, unsigned char *sha1,
 				     p->one->path);
 	}
 
-	git_SHA1_Final(sha1, &ctx);
+	git_SHA1_Final(oid->hash, &ctx);
 	return 0;
 }
 
-int diff_flush_patch_id(struct diff_options *options, unsigned char *sha1, int diff_header_only)
+int diff_flush_patch_id(struct diff_options *options, struct object_id *oid, int diff_header_only)
 {
 	struct diff_queue_struct *q = &diff_queued_diff;
 	int i;
-	int result = diff_get_patch_id(options, sha1, diff_header_only);
+	int result = diff_get_patch_id(options, oid, diff_header_only);
 
 	for (i = 0; i < q->nr; i++)
 		diff_free_filepair(q->queue[i]);
@@ -5077,8 +5077,8 @@ static int is_submodule_ignored(const char *path, struct diff_options *options)
 
 void diff_addremove(struct diff_options *options,
 		    int addremove, unsigned mode,
-		    const unsigned char *sha1,
-		    int sha1_valid,
+		    const struct object_id *oid,
+		    int oid_valid,
 		    const char *concatpath, unsigned dirty_submodule)
 {
 	struct diff_filespec *one, *two;
@@ -5110,9 +5110,9 @@ void diff_addremove(struct diff_options *options,
 	two = alloc_filespec(concatpath);
 
 	if (addremove != '+')
-		fill_filespec(one, sha1, sha1_valid, mode);
+		fill_filespec(one, oid, oid_valid, mode);
 	if (addremove != '-') {
-		fill_filespec(two, sha1, sha1_valid, mode);
+		fill_filespec(two, oid, oid_valid, mode);
 		two->dirty_submodule = dirty_submodule;
 	}
 
@@ -5123,9 +5123,9 @@ void diff_addremove(struct diff_options *options,
 
 void diff_change(struct diff_options *options,
 		 unsigned old_mode, unsigned new_mode,
-		 const unsigned char *old_sha1,
-		 const unsigned char *new_sha1,
-		 int old_sha1_valid, int new_sha1_valid,
+		 const struct object_id *old_oid,
+		 const struct object_id *new_oid,
+		 int old_oid_valid, int new_oid_valid,
 		 const char *concatpath,
 		 unsigned old_dirty_submodule, unsigned new_dirty_submodule)
 {
@@ -5138,8 +5138,8 @@ void diff_change(struct diff_options *options,
 
 	if (DIFF_OPT_TST(options, REVERSE_DIFF)) {
 		SWAP(old_mode, new_mode);
-		SWAP(old_sha1, new_sha1);
-		SWAP(old_sha1_valid, new_sha1_valid);
+		SWAP(old_oid, new_oid);
+		SWAP(old_oid_valid, new_oid_valid);
 		SWAP(old_dirty_submodule, new_dirty_submodule);
 	}
 
@@ -5149,8 +5149,8 @@ void diff_change(struct diff_options *options,
 
 	one = alloc_filespec(concatpath);
 	two = alloc_filespec(concatpath);
-	fill_filespec(one, old_sha1, old_sha1_valid, old_mode);
-	fill_filespec(two, new_sha1, new_sha1_valid, new_mode);
+	fill_filespec(one, old_oid, old_oid_valid, old_mode);
+	fill_filespec(two, new_oid, new_oid_valid, new_mode);
 	one->dirty_submodule = old_dirty_submodule;
 	two->dirty_submodule = new_dirty_submodule;
 	p = diff_queue(&diff_queued_diff, one, two);
@@ -5277,7 +5277,7 @@ int textconv_object(const char *path,
 	struct userdiff_driver *textconv;
 
 	df = alloc_filespec(path);
-	fill_filespec(df, oid->hash, oid_valid, mode);
+	fill_filespec(df, oid, oid_valid, mode);
 	textconv = get_textconv(df);
 	if (!textconv) {
 		free_filespec(df);
diff --git a/diff.h b/diff.h
index 67537f17ed..2d442e296f 100644
--- a/diff.h
+++ b/diff.h
@@ -23,16 +23,16 @@ typedef int (*pathchange_fn_t)(struct diff_options *options,
 
 typedef void (*change_fn_t)(struct diff_options *options,
 		 unsigned old_mode, unsigned new_mode,
-		 const unsigned char *old_sha1,
-		 const unsigned char *new_sha1,
-		 int old_sha1_valid, int new_sha1_valid,
+		 const struct object_id *old_oid,
+		 const struct object_id *new_oid,
+		 int old_oid_valid, int new_oid_valid,
 		 const char *fullpath,
 		 unsigned old_dirty_submodule, unsigned new_dirty_submodule);
 
 typedef void (*add_remove_fn_t)(struct diff_options *options,
 		    int addremove, unsigned mode,
-		    const unsigned char *sha1,
-		    int sha1_valid,
+		    const struct object_id *oid,
+		    int oid_valid,
 		    const char *fullpath, unsigned dirty_submodule);
 
 typedef void (*diff_format_fn_t)(struct diff_queue_struct *q,
@@ -210,13 +210,14 @@ const char *diff_line_prefix(struct diff_options *);
 extern const char mime_boundary_leader[];
 
 extern struct combine_diff_path *diff_tree_paths(
-	struct combine_diff_path *p, const unsigned char *sha1,
-	const unsigned char **parent_sha1, int nparent,
+	struct combine_diff_path *p, const struct object_id *oid,
+	const struct object_id **parents_oid, int nparent,
 	struct strbuf *base, struct diff_options *opt);
-extern int diff_tree_sha1(const unsigned char *old, const unsigned char *new,
-			  const char *base, struct diff_options *opt);
-extern int diff_root_tree_sha1(const unsigned char *new, const char *base,
-                               struct diff_options *opt);
+extern int diff_tree_oid(const struct object_id *old_oid,
+			 const struct object_id *new_oid,
+			 const char *base, struct diff_options *opt);
+extern int diff_root_tree_oid(const struct object_id *new_oid, const char *base,
+			      struct diff_options *opt);
 
 struct combine_diff_path {
 	struct combine_diff_path *next;
@@ -236,7 +237,7 @@ struct combine_diff_path {
 extern void show_combined_diff(struct combine_diff_path *elem, int num_parent,
 			      int dense, struct rev_info *);
 
-extern void diff_tree_combined(const unsigned char *sha1, const struct oid_array *parents, int dense, struct rev_info *rev);
+extern void diff_tree_combined(const struct object_id *oid, const struct oid_array *parents, int dense, struct rev_info *rev);
 
 extern void diff_tree_combined_merge(const struct commit *commit, int dense, struct rev_info *rev);
 
@@ -247,16 +248,15 @@ extern int diff_can_quit_early(struct diff_options *);
 extern void diff_addremove(struct diff_options *,
 			   int addremove,
 			   unsigned mode,
-			   const unsigned char *sha1,
-			   int sha1_valid,
+			   const struct object_id *oid,
+			   int oid_valid,
 			   const char *fullpath, unsigned dirty_submodule);
 
 extern void diff_change(struct diff_options *,
 			unsigned mode1, unsigned mode2,
-			const unsigned char *sha1,
-			const unsigned char *sha2,
-			int sha1_valid,
-			int sha2_valid,
+			const struct object_id *old_oid,
+			const struct object_id *new_oid,
+			int old_oid_valid, int new_oid_valid,
 			const char *fullpath,
 			unsigned dirty_submodule1, unsigned dirty_submodule2);
 
@@ -355,7 +355,7 @@ extern int run_diff_files(struct rev_info *revs, unsigned int option);
 extern int run_diff_index(struct rev_info *revs, int cached);
 
 extern int do_diff_cache(const struct object_id *, struct diff_options *);
-extern int diff_flush_patch_id(struct diff_options *, unsigned char *, int);
+extern int diff_flush_patch_id(struct diff_options *, struct object_id *, int);
 
 extern int diff_result_code(struct diff_options *, int);
 
diff --git a/diffcore-rename.c b/diffcore-rename.c
index f7444c86bd..03d1e8d40b 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -60,7 +60,7 @@ static int add_rename_dst(struct diff_filespec *two)
 		memmove(rename_dst + first + 1, rename_dst + first,
 			(rename_dst_nr - first - 1) * sizeof(*rename_dst));
 	rename_dst[first].two = alloc_filespec(two->path);
-	fill_filespec(rename_dst[first].two, two->oid.hash, two->oid_valid,
+	fill_filespec(rename_dst[first].two, &two->oid, two->oid_valid,
 		      two->mode);
 	rename_dst[first].pair = NULL;
 	return 0;
@@ -464,7 +464,7 @@ void diffcore_rename(struct diff_options *options)
 				 strcmp(options->single_follow, p->two->path))
 				continue; /* not interested */
 			else if (!DIFF_OPT_TST(options, RENAME_EMPTY) &&
-				 is_empty_blob_sha1(p->two->oid.hash))
+				 is_empty_blob_oid(&p->two->oid))
 				continue;
 			else if (add_rename_dst(p->two) < 0) {
 				warning("skipping rename detection, detected"
@@ -474,7 +474,7 @@ void diffcore_rename(struct diff_options *options)
 			}
 		}
 		else if (!DIFF_OPT_TST(options, RENAME_EMPTY) &&
-			 is_empty_blob_sha1(p->one->oid.hash))
+			 is_empty_blob_oid(&p->one->oid))
 			continue;
 		else if (!DIFF_PAIR_UNMERGED(p) && !DIFF_FILE_VALID(p->two)) {
 			/*
diff --git a/diffcore.h b/diffcore.h
index 6230241354..a30da161da 100644
--- a/diffcore.h
+++ b/diffcore.h
@@ -52,7 +52,7 @@ struct diff_filespec {
 
 extern struct diff_filespec *alloc_filespec(const char *);
 extern void free_filespec(struct diff_filespec *);
-extern void fill_filespec(struct diff_filespec *, const unsigned char *,
+extern void fill_filespec(struct diff_filespec *, const struct object_id *,
 			  int, unsigned short);
 
 #define CHECK_SIZE_ONLY 1
diff --git a/grep.c b/grep.c
index d0bf37858a..d7ef21358e 100644
--- a/grep.c
+++ b/grep.c
@@ -1584,11 +1584,11 @@ static int fill_textconv_grep(struct userdiff_driver *driver,
 	 */
 	df = alloc_filespec(gs->path);
 	switch (gs->type) {
-	case GREP_SOURCE_SHA1:
+	case GREP_SOURCE_OID:
 		fill_filespec(df, gs->identifier, 1, 0100644);
 		break;
 	case GREP_SOURCE_FILE:
-		fill_filespec(df, null_sha1, 0, 0100644);
+		fill_filespec(df, &null_oid, 0, 0100644);
 		break;
 	default:
 		die("BUG: attempt to textconv something without a path?");
@@ -1928,9 +1928,8 @@ void grep_source_init(struct grep_source *gs, enum grep_source_type type,
 		 * If the identifier is non-NULL (in the submodule case) it
 		 * will be a SHA1 that needs to be copied.
 		 */
-	case GREP_SOURCE_SHA1:
-		gs->identifier = xmalloc(20);
-		hashcpy(gs->identifier, identifier);
+	case GREP_SOURCE_OID:
+		gs->identifier = oiddup(identifier);
 		break;
 	case GREP_SOURCE_BUF:
 		gs->identifier = NULL;
@@ -1953,7 +1952,7 @@ void grep_source_clear_data(struct grep_source *gs)
 {
 	switch (gs->type) {
 	case GREP_SOURCE_FILE:
-	case GREP_SOURCE_SHA1:
+	case GREP_SOURCE_OID:
 	case GREP_SOURCE_SUBMODULE:
 		free(gs->buf);
 		gs->buf = NULL;
@@ -1965,7 +1964,7 @@ void grep_source_clear_data(struct grep_source *gs)
 	}
 }
 
-static int grep_source_load_sha1(struct grep_source *gs)
+static int grep_source_load_oid(struct grep_source *gs)
 {
 	enum object_type type;
 
@@ -1976,7 +1975,7 @@ static int grep_source_load_sha1(struct grep_source *gs)
 	if (!gs->buf)
 		return error(_("'%s': unable to read %s"),
 			     gs->name,
-			     sha1_to_hex(gs->identifier));
+			     oid_to_hex(gs->identifier));
 	return 0;
 }
 
@@ -2022,8 +2021,8 @@ static int grep_source_load(struct grep_source *gs)
 	switch (gs->type) {
 	case GREP_SOURCE_FILE:
 		return grep_source_load_file(gs);
-	case GREP_SOURCE_SHA1:
-		return grep_source_load_sha1(gs);
+	case GREP_SOURCE_OID:
+		return grep_source_load_oid(gs);
 	case GREP_SOURCE_BUF:
 		return gs->buf ? 0 : -1;
 	case GREP_SOURCE_SUBMODULE:
diff --git a/grep.h b/grep.h
index 6f3d4e1954..b8f93bfc2d 100644
--- a/grep.h
+++ b/grep.h
@@ -191,7 +191,7 @@ struct grep_source {
 	char *name;
 
 	enum grep_source_type {
-		GREP_SOURCE_SHA1,
+		GREP_SOURCE_OID,
 		GREP_SOURCE_FILE,
 		GREP_SOURCE_BUF,
 		GREP_SOURCE_SUBMODULE,
diff --git a/line-log.c b/line-log.c
index b9087814b8..2588ce0767 100644
--- a/line-log.c
+++ b/line-log.c
@@ -500,12 +500,12 @@ static struct commit *check_single_commit(struct rev_info *revs)
 static void fill_blob_sha1(struct commit *commit, struct diff_filespec *spec)
 {
 	unsigned mode;
-	unsigned char sha1[20];
+	struct object_id oid;
 
 	if (get_tree_entry(commit->object.oid.hash, spec->path,
-			   sha1, &mode))
+			   oid.hash, &mode))
 		die("There is no path %s in the commit", spec->path);
-	fill_filespec(spec, sha1, 1, mode);
+	fill_filespec(spec, &oid, 1, mode);
 
 	return;
 }
@@ -819,8 +819,8 @@ static void queue_diffs(struct line_log_data *range,
 	assert(commit);
 
 	DIFF_QUEUE_CLEAR(&diff_queued_diff);
-	diff_tree_sha1(parent ? parent->tree->object.oid.hash : NULL,
-			commit->tree->object.oid.hash, "", opt);
+	diff_tree_oid(parent ? &parent->tree->object.oid : NULL,
+		      &commit->tree->object.oid, "", opt);
 	if (opt->detect_rename) {
 		filter_diffs_for_paths(range, 1);
 		if (diff_might_be_rename())
diff --git a/log-tree.c b/log-tree.c
index a4ec11c2bf..2903874ecf 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -655,7 +655,7 @@ void show_log(struct rev_info *opt)
 		struct strbuf notebuf = STRBUF_INIT;
 
 		raw = (opt->commit_format == CMIT_FMT_USERFORMAT);
-		format_display_notes(commit->object.oid.hash, &notebuf,
+		format_display_notes(&commit->object.oid, &notebuf,
 				     get_log_output_encoding(), raw);
 		ctx.notes_message = notebuf.len
 			? strbuf_detach(&notebuf, NULL)
@@ -803,7 +803,7 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
 	parents = get_saved_parents(opt, commit);
 	if (!parents) {
 		if (opt->show_root_diff) {
-			diff_root_tree_sha1(oid->hash, "", &opt->diffopt);
+			diff_root_tree_oid(oid, "", &opt->diffopt);
 			log_tree_diff_flush(opt);
 		}
 		return !opt->loginfo;
@@ -822,8 +822,8 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
 			 * we merged _in_.
 			 */
 			parse_commit_or_die(parents->item);
-			diff_tree_sha1(parents->item->tree->object.oid.hash,
-				       oid->hash, "", &opt->diffopt);
+			diff_tree_oid(&parents->item->tree->object.oid,
+				      oid, "", &opt->diffopt);
 			log_tree_diff_flush(opt);
 			return !opt->loginfo;
 		}
@@ -837,8 +837,8 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
 		struct commit *parent = parents->item;
 
 		parse_commit_or_die(parent);
-		diff_tree_sha1(parent->tree->object.oid.hash,
-			       oid->hash, "", &opt->diffopt);
+		diff_tree_oid(&parent->tree->object.oid,
+			      oid, "", &opt->diffopt);
 		log_tree_diff_flush(opt);
 
 		showed_log |= !opt->loginfo;
diff --git a/merge-recursive.c b/merge-recursive.c
index ae5238d82c..5cc86df2d1 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -528,7 +528,7 @@ static struct string_list *get_renames(struct merge_options *o,
 	opts.show_rename_progress = o->show_rename_progress;
 	opts.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_setup_done(&opts);
-	diff_tree_sha1(o_tree->object.oid.hash, tree->object.oid.hash, "", &opts);
+	diff_tree_oid(&o_tree->object.oid, &tree->object.oid, "", &opts);
 	diffcore_std(&opts);
 	if (opts.needed_rename_limit > o->needed_rename_limit)
 		o->needed_rename_limit = opts.needed_rename_limit;
diff --git a/notes-cache.c b/notes-cache.c
index 2843e98576..29b4cede5f 100644
--- a/notes-cache.c
+++ b/notes-cache.c
@@ -69,15 +69,15 @@ int notes_cache_write(struct notes_cache *c)
 char *notes_cache_get(struct notes_cache *c, struct object_id *key_oid,
 		      size_t *outsize)
 {
-	const unsigned char *value_sha1;
+	const struct object_id *value_oid;
 	enum object_type type;
 	char *value;
 	unsigned long size;
 
-	value_sha1 = get_note(&c->tree, key_oid->hash);
-	if (!value_sha1)
+	value_oid = get_note(&c->tree, key_oid);
+	if (!value_oid)
 		return NULL;
-	value = read_sha1_file(value_sha1, &type, &size);
+	value = read_sha1_file(value_oid->hash, &type, &size);
 
 	*outsize = size;
 	return value;
@@ -90,5 +90,5 @@ int notes_cache_put(struct notes_cache *c, struct object_id *key_oid,
 
 	if (write_sha1_file(data, size, "blob", value_oid.hash) < 0)
 		return -1;
-	return add_note(&c->tree, key_oid->hash, value_oid.hash, NULL);
+	return add_note(&c->tree, key_oid, &value_oid, NULL);
 }
diff --git a/notes-merge.c b/notes-merge.c
index 6244f6af9c..70e3fbeefb 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -22,21 +22,21 @@ void init_notes_merge_options(struct notes_merge_options *o)
 	o->verbosity = NOTES_MERGE_VERBOSITY_DEFAULT;
 }
 
-static int path_to_sha1(const char *path, unsigned char *sha1)
+static int path_to_oid(const char *path, struct object_id *oid)
 {
-	char hex_sha1[40];
+	char hex_oid[GIT_SHA1_HEXSZ];
 	int i = 0;
-	while (*path && i < 40) {
+	while (*path && i < GIT_SHA1_HEXSZ) {
 		if (*path != '/')
-			hex_sha1[i++] = *path;
+			hex_oid[i++] = *path;
 		path++;
 	}
-	if (*path || i != 40)
+	if (*path || i != GIT_SHA1_HEXSZ)
 		return -1;
-	return get_sha1_hex(hex_sha1, sha1);
+	return get_oid_hex(hex_oid, oid);
 }
 
-static int verify_notes_filepair(struct diff_filepair *p, unsigned char *sha1)
+static int verify_notes_filepair(struct diff_filepair *p, struct object_id *oid)
 {
 	switch (p->status) {
 	case DIFF_STATUS_MODIFIED:
@@ -54,11 +54,11 @@ static int verify_notes_filepair(struct diff_filepair *p, unsigned char *sha1)
 		return -1;
 	}
 	assert(!strcmp(p->one->path, p->two->path));
-	return path_to_sha1(p->one->path, sha1);
+	return path_to_oid(p->one->path, oid);
 }
 
 static struct notes_merge_pair *find_notes_merge_pair_pos(
-		struct notes_merge_pair *list, int len, unsigned char *obj,
+		struct notes_merge_pair *list, int len, struct object_id *obj,
 		int insert_new, int *occupied)
 {
 	/*
@@ -75,7 +75,7 @@ static struct notes_merge_pair *find_notes_merge_pair_pos(
 	int i = last_index < len ? last_index : len - 1;
 	int prev_cmp = 0, cmp = -1;
 	while (i >= 0 && i < len) {
-		cmp = hashcmp(obj, list[i].obj.hash);
+		cmp = oidcmp(obj, &list[i].obj);
 		if (!cmp) /* obj belongs @ i */
 			break;
 		else if (cmp < 0 && prev_cmp <= 0) /* obj belongs < i */
@@ -114,8 +114,8 @@ static struct object_id uninitialized = {
 };
 
 static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
-						 const unsigned char *base,
-						 const unsigned char *remote,
+						 const struct object_id *base,
+						 const struct object_id *remote,
 						 int *num_changes)
 {
 	struct diff_options opt;
@@ -123,13 +123,13 @@ static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
 	int i, len = 0;
 
 	trace_printf("\tdiff_tree_remote(base = %.7s, remote = %.7s)\n",
-	       sha1_to_hex(base), sha1_to_hex(remote));
+	       oid_to_hex(base), oid_to_hex(remote));
 
 	diff_setup(&opt);
 	DIFF_OPT_SET(&opt, RECURSIVE);
 	opt.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_setup_done(&opt);
-	diff_tree_sha1(base, remote, "", &opt);
+	diff_tree_oid(base, remote, "", &opt);
 	diffcore_std(&opt);
 
 	changes = xcalloc(diff_queued_diff.nr, sizeof(struct notes_merge_pair));
@@ -138,19 +138,19 @@ static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
 		struct diff_filepair *p = diff_queued_diff.queue[i];
 		struct notes_merge_pair *mp;
 		int occupied;
-		unsigned char obj[20];
+		struct object_id obj;
 
-		if (verify_notes_filepair(p, obj)) {
+		if (verify_notes_filepair(p, &obj)) {
 			trace_printf("\t\tCannot merge entry '%s' (%c): "
 			       "%.7s -> %.7s. Skipping!\n", p->one->path,
 			       p->status, oid_to_hex(&p->one->oid),
 			       oid_to_hex(&p->two->oid));
 			continue;
 		}
-		mp = find_notes_merge_pair_pos(changes, len, obj, 1, &occupied);
+		mp = find_notes_merge_pair_pos(changes, len, &obj, 1, &occupied);
 		if (occupied) {
 			/* We've found an addition/deletion pair */
-			assert(!hashcmp(mp->obj.hash, obj));
+			assert(!oidcmp(&mp->obj, &obj));
 			if (is_null_oid(&p->one->oid)) { /* addition */
 				assert(is_null_oid(&mp->remote));
 				oidcpy(&mp->remote, &p->two->oid);
@@ -160,7 +160,7 @@ static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
 			} else
 				assert(!"Invalid existing change recorded");
 		} else {
-			hashcpy(mp->obj.hash, obj);
+			oidcpy(&mp->obj, &obj);
 			oidcpy(&mp->base, &p->one->oid);
 			oidcpy(&mp->local, &uninitialized);
 			oidcpy(&mp->remote, &p->two->oid);
@@ -179,45 +179,45 @@ static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
 
 static void diff_tree_local(struct notes_merge_options *o,
 			    struct notes_merge_pair *changes, int len,
-			    const unsigned char *base,
-			    const unsigned char *local)
+			    const struct object_id *base,
+			    const struct object_id *local)
 {
 	struct diff_options opt;
 	int i;
 
 	trace_printf("\tdiff_tree_local(len = %i, base = %.7s, local = %.7s)\n",
-	       len, sha1_to_hex(base), sha1_to_hex(local));
+	       len, oid_to_hex(base), oid_to_hex(local));
 
 	diff_setup(&opt);
 	DIFF_OPT_SET(&opt, RECURSIVE);
 	opt.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_setup_done(&opt);
-	diff_tree_sha1(base, local, "", &opt);
+	diff_tree_oid(base, local, "", &opt);
 	diffcore_std(&opt);
 
 	for (i = 0; i < diff_queued_diff.nr; i++) {
 		struct diff_filepair *p = diff_queued_diff.queue[i];
 		struct notes_merge_pair *mp;
 		int match;
-		unsigned char obj[20];
+		struct object_id obj;
 
-		if (verify_notes_filepair(p, obj)) {
+		if (verify_notes_filepair(p, &obj)) {
 			trace_printf("\t\tCannot merge entry '%s' (%c): "
 			       "%.7s -> %.7s. Skipping!\n", p->one->path,
 			       p->status, oid_to_hex(&p->one->oid),
 			       oid_to_hex(&p->two->oid));
 			continue;
 		}
-		mp = find_notes_merge_pair_pos(changes, len, obj, 0, &match);
+		mp = find_notes_merge_pair_pos(changes, len, &obj, 0, &match);
 		if (!match) {
 			trace_printf("\t\tIgnoring local-only change for %s: "
-			       "%.7s -> %.7s\n", sha1_to_hex(obj),
+			       "%.7s -> %.7s\n", oid_to_hex(&obj),
 			       oid_to_hex(&p->one->oid),
 			       oid_to_hex(&p->two->oid));
 			continue;
 		}
 
-		assert(!hashcmp(mp->obj.hash, obj));
+		assert(!oidcmp(&mp->obj, &obj));
 		if (is_null_oid(&p->two->oid)) { /* deletion */
 			/*
 			 * Either this is a true deletion (1), or it is part
@@ -292,11 +292,11 @@ static void check_notes_merge_worktree(struct notes_merge_options *o)
 		    git_path(NOTES_MERGE_WORKTREE));
 }
 
-static void write_buf_to_worktree(const unsigned char *obj,
+static void write_buf_to_worktree(const struct object_id *obj,
 				  const char *buf, unsigned long size)
 {
 	int fd;
-	char *path = git_pathdup(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
+	char *path = git_pathdup(NOTES_MERGE_WORKTREE "/%s", oid_to_hex(obj));
 	if (safe_create_leading_directories_const(path))
 		die_errno("unable to create directory for '%s'", path);
 
@@ -320,19 +320,19 @@ static void write_buf_to_worktree(const unsigned char *obj,
 	free(path);
 }
 
-static void write_note_to_worktree(const unsigned char *obj,
-				   const unsigned char *note)
+static void write_note_to_worktree(const struct object_id *obj,
+				   const struct object_id *note)
 {
 	enum object_type type;
 	unsigned long size;
-	void *buf = read_sha1_file(note, &type, &size);
+	void *buf = read_sha1_file(note->hash, &type, &size);
 
 	if (!buf)
 		die("cannot read note %s for object %s",
-		    sha1_to_hex(note), sha1_to_hex(obj));
+		    oid_to_hex(note), oid_to_hex(obj));
 	if (type != OBJ_BLOB)
 		die("blob expected in note %s for object %s",
-		    sha1_to_hex(note), sha1_to_hex(obj));
+		    oid_to_hex(note), oid_to_hex(obj));
 	write_buf_to_worktree(obj, buf, size);
 	free(buf);
 }
@@ -358,7 +358,7 @@ static int ll_merge_in_worktree(struct notes_merge_options *o,
 	if ((status < 0) || !result_buf.ptr)
 		die("Failed to execute internal merge");
 
-	write_buf_to_worktree(p->obj.hash, result_buf.ptr, result_buf.size);
+	write_buf_to_worktree(&p->obj, result_buf.ptr, result_buf.size);
 	free(result_buf.ptr);
 
 	return status;
@@ -393,7 +393,7 @@ static int merge_one_change_manual(struct notes_merge_options *o,
 				"deleted in %s and modified in %s. Version from %s "
 				"left in tree.\n",
 				oid_to_hex(&p->obj), lref, rref, rref);
-		write_note_to_worktree(p->obj.hash, p->remote.hash);
+		write_note_to_worktree(&p->obj, &p->remote);
 	} else if (is_null_oid(&p->remote)) {
 		/* D/F conflict, checkout p->local */
 		assert(!is_null_oid(&p->local));
@@ -402,7 +402,7 @@ static int merge_one_change_manual(struct notes_merge_options *o,
 				"deleted in %s and modified in %s. Version from %s "
 				"left in tree.\n",
 				oid_to_hex(&p->obj), rref, lref, lref);
-		write_note_to_worktree(p->obj.hash, p->local.hash);
+		write_note_to_worktree(&p->obj, &p->local);
 	} else {
 		/* "regular" conflict, checkout result of ll_merge() */
 		const char *reason = "content";
@@ -444,14 +444,14 @@ static int merge_one_change(struct notes_merge_options *o,
 		if (o->verbosity >= 2)
 			printf("Using remote notes for %s\n",
 						oid_to_hex(&p->obj));
-		if (add_note(t, p->obj.hash, p->remote.hash, combine_notes_overwrite))
+		if (add_note(t, &p->obj, &p->remote, combine_notes_overwrite))
 			die("BUG: combine_notes_overwrite failed");
 		return 0;
 	case NOTES_MERGE_RESOLVE_UNION:
 		if (o->verbosity >= 2)
 			printf("Concatenating local and remote notes for %s\n",
 							oid_to_hex(&p->obj));
-		if (add_note(t, p->obj.hash, p->remote.hash, combine_notes_concatenate))
+		if (add_note(t, &p->obj, &p->remote, combine_notes_concatenate))
 			die("failed to concatenate notes "
 			    "(combine_notes_concatenate)");
 		return 0;
@@ -459,7 +459,7 @@ static int merge_one_change(struct notes_merge_options *o,
 		if (o->verbosity >= 2)
 			printf("Concatenating unique lines in local and remote "
 				"notes for %s\n", oid_to_hex(&p->obj));
-		if (add_note(t, p->obj.hash, p->remote.hash, combine_notes_cat_sort_uniq))
+		if (add_note(t, &p->obj, &p->remote, combine_notes_cat_sort_uniq))
 			die("failed to concatenate notes "
 			    "(combine_notes_cat_sort_uniq)");
 		return 0;
@@ -491,7 +491,7 @@ static int merge_changes(struct notes_merge_options *o,
 			   !oidcmp(&p->local, &p->base)) {
 			/* no local change; adopt remote change */
 			trace_printf("\t\t\tno local change, adopted remote\n");
-			if (add_note(t, p->obj.hash, p->remote.hash,
+			if (add_note(t, &p->obj, &p->remote,
 				     combine_notes_overwrite))
 				die("BUG: combine_notes_overwrite failed");
 		} else {
@@ -505,16 +505,17 @@ static int merge_changes(struct notes_merge_options *o,
 }
 
 static int merge_from_diffs(struct notes_merge_options *o,
-			    const unsigned char *base,
-			    const unsigned char *local,
-			    const unsigned char *remote, struct notes_tree *t)
+			    const struct object_id *base,
+			    const struct object_id *local,
+			    const struct object_id *remote,
+			    struct notes_tree *t)
 {
 	struct notes_merge_pair *changes;
 	int num_changes, conflicts;
 
 	trace_printf("\tmerge_from_diffs(base = %.7s, local = %.7s, "
-	       "remote = %.7s)\n", sha1_to_hex(base), sha1_to_hex(local),
-	       sha1_to_hex(remote));
+	       "remote = %.7s)\n", oid_to_hex(base), oid_to_hex(local),
+	       oid_to_hex(remote));
 
 	changes = diff_tree_remote(o, base, remote, &num_changes);
 	diff_tree_local(o, changes, num_changes, base, local);
@@ -533,17 +534,17 @@ static int merge_from_diffs(struct notes_merge_options *o,
 
 int notes_merge(struct notes_merge_options *o,
 		struct notes_tree *local_tree,
-		unsigned char *result_sha1)
+		struct object_id *result_oid)
 {
 	struct object_id local_oid, remote_oid;
 	struct commit *local, *remote;
 	struct commit_list *bases = NULL;
-	const unsigned char *base_sha1, *base_tree_sha1;
+	const struct object_id *base_oid, *base_tree_oid;
 	int result = 0;
 
 	assert(o->local_ref && o->remote_ref);
 	assert(!strcmp(o->local_ref, local_tree->ref));
-	hashclr(result_sha1);
+	oidclr(result_oid);
 
 	trace_printf("notes_merge(o->local_ref = %s, o->remote_ref = %s)\n",
 	       o->local_ref, o->remote_ref);
@@ -553,16 +554,16 @@ int notes_merge(struct notes_merge_options *o,
 		die("Failed to resolve local notes ref '%s'", o->local_ref);
 	else if (!check_refname_format(o->local_ref, 0) &&
 		is_null_oid(&local_oid))
-		local = NULL; /* local_sha1 == null_sha1 indicates unborn ref */
+		local = NULL; /* local_oid == null_oid indicates unborn ref */
 	else if (!(local = lookup_commit_reference(&local_oid)))
 		die("Could not parse local commit %s (%s)",
 		    oid_to_hex(&local_oid), o->local_ref);
 	trace_printf("\tlocal commit: %.7s\n", oid_to_hex(&local_oid));
 
-	/* Dereference o->remote_ref into remote_sha1 */
+	/* Dereference o->remote_ref into remote_oid */
 	if (get_oid(o->remote_ref, &remote_oid)) {
 		/*
-		 * Failed to get remote_sha1. If o->remote_ref looks like an
+		 * Failed to get remote_oid. If o->remote_ref looks like an
 		 * unborn ref, perform the merge using an empty notes tree.
 		 */
 		if (!check_refname_format(o->remote_ref, 0)) {
@@ -583,12 +584,12 @@ int notes_merge(struct notes_merge_options *o,
 		    "(%s)", o->remote_ref, o->local_ref);
 	if (!local) {
 		/* result == remote commit */
-		hashcpy(result_sha1, remote_oid.hash);
+		oidcpy(result_oid, &remote_oid);
 		goto found_result;
 	}
 	if (!remote) {
 		/* result == local commit */
-		hashcpy(result_sha1, local_oid.hash);
+		oidcpy(result_oid, &local_oid);
 		goto found_result;
 	}
 	assert(local && remote);
@@ -596,48 +597,48 @@ int notes_merge(struct notes_merge_options *o,
 	/* Find merge bases */
 	bases = get_merge_bases(local, remote);
 	if (!bases) {
-		base_sha1 = null_sha1;
-		base_tree_sha1 = EMPTY_TREE_SHA1_BIN;
+		base_oid = &null_oid;
+		base_tree_oid = &empty_tree_oid;
 		if (o->verbosity >= 4)
 			printf("No merge base found; doing history-less merge\n");
 	} else if (!bases->next) {
-		base_sha1 = bases->item->object.oid.hash;
-		base_tree_sha1 = bases->item->tree->object.oid.hash;
+		base_oid = &bases->item->object.oid;
+		base_tree_oid = &bases->item->tree->object.oid;
 		if (o->verbosity >= 4)
 			printf("One merge base found (%.7s)\n",
-				sha1_to_hex(base_sha1));
+			       oid_to_hex(base_oid));
 	} else {
 		/* TODO: How to handle multiple merge-bases? */
-		base_sha1 = bases->item->object.oid.hash;
-		base_tree_sha1 = bases->item->tree->object.oid.hash;
+		base_oid = &bases->item->object.oid;
+		base_tree_oid = &bases->item->tree->object.oid;
 		if (o->verbosity >= 3)
 			printf("Multiple merge bases found. Using the first "
-				"(%.7s)\n", sha1_to_hex(base_sha1));
+				"(%.7s)\n", oid_to_hex(base_oid));
 	}
 
 	if (o->verbosity >= 4)
 		printf("Merging remote commit %.7s into local commit %.7s with "
 			"merge-base %.7s\n", oid_to_hex(&remote->object.oid),
 			oid_to_hex(&local->object.oid),
-			sha1_to_hex(base_sha1));
+			oid_to_hex(base_oid));
 
-	if (!hashcmp(remote->object.oid.hash, base_sha1)) {
+	if (!oidcmp(&remote->object.oid, base_oid)) {
 		/* Already merged; result == local commit */
 		if (o->verbosity >= 2)
 			printf("Already up-to-date!\n");
-		hashcpy(result_sha1, local->object.oid.hash);
+		oidcpy(result_oid, &local->object.oid);
 		goto found_result;
 	}
-	if (!hashcmp(local->object.oid.hash, base_sha1)) {
+	if (!oidcmp(&local->object.oid, base_oid)) {
 		/* Fast-forward; result == remote commit */
 		if (o->verbosity >= 2)
 			printf("Fast-forward\n");
-		hashcpy(result_sha1, remote->object.oid.hash);
+		oidcpy(result_oid, &remote->object.oid);
 		goto found_result;
 	}
 
-	result = merge_from_diffs(o, base_tree_sha1, local->tree->object.oid.hash,
-				  remote->tree->object.oid.hash, local_tree);
+	result = merge_from_diffs(o, base_tree_oid, &local->tree->object.oid,
+				  &remote->tree->object.oid, local_tree);
 
 	if (result != 0) { /* non-trivial merge (with or without conflicts) */
 		/* Commit (partial) result */
@@ -646,28 +647,28 @@ int notes_merge(struct notes_merge_options *o,
 		commit_list_insert(local, &parents);
 		create_notes_commit(local_tree, parents,
 				    o->commit_msg.buf, o->commit_msg.len,
-				    result_sha1);
+				    result_oid->hash);
 	}
 
 found_result:
 	free_commit_list(bases);
 	strbuf_release(&(o->commit_msg));
-	trace_printf("notes_merge(): result = %i, result_sha1 = %.7s\n",
-	       result, sha1_to_hex(result_sha1));
+	trace_printf("notes_merge(): result = %i, result_oid = %.7s\n",
+	       result, oid_to_hex(result_oid));
 	return result;
 }
 
 int notes_merge_commit(struct notes_merge_options *o,
 		       struct notes_tree *partial_tree,
 		       struct commit *partial_commit,
-		       unsigned char *result_sha1)
+		       struct object_id *result_oid)
 {
 	/*
 	 * Iterate through files in .git/NOTES_MERGE_WORKTREE and add all
 	 * found notes to 'partial_tree'. Write the updated notes tree to
 	 * the DB, and commit the resulting tree object while reusing the
 	 * commit message and parents from 'partial_commit'.
-	 * Finally store the new commit object SHA1 into 'result_sha1'.
+	 * Finally store the new commit object OID into 'result_oid'.
 	 */
 	DIR *dir;
 	struct dirent *e;
@@ -693,12 +694,12 @@ int notes_merge_commit(struct notes_merge_options *o,
 	baselen = path.len;
 	while ((e = readdir(dir)) != NULL) {
 		struct stat st;
-		unsigned char obj_sha1[20], blob_sha1[20];
+		struct object_id obj_oid, blob_oid;
 
 		if (is_dot_or_dotdot(e->d_name))
 			continue;
 
-		if (strlen(e->d_name) != 40 || get_sha1_hex(e->d_name, obj_sha1)) {
+		if (get_oid_hex(e->d_name, &obj_oid)) {
 			if (o->verbosity >= 3)
 				printf("Skipping non-SHA1 entry '%s%s'\n",
 					path.buf, e->d_name);
@@ -709,23 +710,23 @@ int notes_merge_commit(struct notes_merge_options *o,
 		/* write file as blob, and add to partial_tree */
 		if (stat(path.buf, &st))
 			die_errno("Failed to stat '%s'", path.buf);
-		if (index_path(blob_sha1, path.buf, &st, HASH_WRITE_OBJECT))
+		if (index_path(blob_oid.hash, path.buf, &st, HASH_WRITE_OBJECT))
 			die("Failed to write blob object from '%s'", path.buf);
-		if (add_note(partial_tree, obj_sha1, blob_sha1, NULL))
+		if (add_note(partial_tree, &obj_oid, &blob_oid, NULL))
 			die("Failed to add resolved note '%s' to notes tree",
 			    path.buf);
 		if (o->verbosity >= 4)
 			printf("Added resolved note for object %s: %s\n",
-				sha1_to_hex(obj_sha1), sha1_to_hex(blob_sha1));
+				oid_to_hex(&obj_oid), oid_to_hex(&blob_oid));
 		strbuf_setlen(&path, baselen);
 	}
 
 	create_notes_commit(partial_tree, partial_commit->parents,
-			    msg, strlen(msg), result_sha1);
+			    msg, strlen(msg), result_oid->hash);
 	unuse_commit_buffer(partial_commit, buffer);
 	if (o->verbosity >= 4)
 		printf("Finalized notes merge commit: %s\n",
-			sha1_to_hex(result_sha1));
+			oid_to_hex(result_oid));
 	strbuf_release(&path);
 	closedir(dir);
 	return 0;
diff --git a/notes-merge.h b/notes-merge.h
index 0d890563b5..f815f23451 100644
--- a/notes-merge.h
+++ b/notes-merge.h
@@ -32,16 +32,16 @@ void init_notes_merge_options(struct notes_merge_options *o);
  * outcomes:
  *
  * 1. The merge trivially results in an existing commit (e.g. fast-forward or
- *    already-up-to-date). 'local_tree' is untouched, the SHA1 of the result
- *    is written into 'result_sha1' and 0 is returned.
+ *    already-up-to-date). 'local_tree' is untouched, the OID of the result
+ *    is written into 'result_oid' and 0 is returned.
  * 2. The merge successfully completes, producing a merge commit. local_tree
- *    contains the updated notes tree, the SHA1 of the resulting commit is
- *    written into 'result_sha1', and 1 is returned.
+ *    contains the updated notes tree, the OID of the resulting commit is
+ *    written into 'result_oid', and 1 is returned.
  * 3. The merge results in conflicts. This is similar to #2 in that the
  *    partial merge result (i.e. merge result minus the unmerged entries)
- *    are stored in 'local_tree', and the SHA1 or the resulting commit
+ *    are stored in 'local_tree', and the OID or the resulting commit
  *    (to be amended when the conflicts have been resolved) is written into
- *    'result_sha1'. The unmerged entries are written into the
+ *    'result_oid'. The unmerged entries are written into the
  *    .git/NOTES_MERGE_WORKTREE directory with conflict markers.
  *    -1 is returned.
  *
@@ -52,7 +52,7 @@ void init_notes_merge_options(struct notes_merge_options *o);
  */
 int notes_merge(struct notes_merge_options *o,
 		struct notes_tree *local_tree,
-		unsigned char *result_sha1);
+		struct object_id *result_oid);
 
 /*
  * Finalize conflict resolution from an earlier notes_merge()
@@ -62,13 +62,13 @@ int notes_merge(struct notes_merge_options *o,
  * call to notes_merge().
  *
  * This function will add the (now resolved) notes in .git/NOTES_MERGE_WORKTREE
- * to 'partial_tree', and create a final notes merge commit, the SHA1 of which
- * will be stored in 'result_sha1'.
+ * to 'partial_tree', and create a final notes merge commit, the OID of which
+ * will be stored in 'result_oid'.
  */
 int notes_merge_commit(struct notes_merge_options *o,
 		       struct notes_tree *partial_tree,
 		       struct commit *partial_commit,
-		       unsigned char *result_sha1);
+		       struct object_id *result_oid);
 
 /*
  * Abort conflict resolution from an earlier notes_merge()
diff --git a/notes-utils.c b/notes-utils.c
index 031503d7b2..9ebf841956 100644
--- a/notes-utils.c
+++ b/notes-utils.c
@@ -158,7 +158,7 @@ struct notes_rewrite_cfg *init_copy_notes_for_rewrite(const char *cmd)
 }
 
 int copy_note_for_rewrite(struct notes_rewrite_cfg *c,
-			  const unsigned char *from_obj, const unsigned char *to_obj)
+			  const struct object_id *from_obj, const struct object_id *to_obj)
 {
 	int ret = 0;
 	int i;
diff --git a/notes-utils.h b/notes-utils.h
index fa538e1d95..1190578398 100644
--- a/notes-utils.h
+++ b/notes-utils.h
@@ -40,7 +40,7 @@ struct notes_rewrite_cfg {
 int parse_notes_merge_strategy(const char *v, enum notes_merge_strategy *s);
 struct notes_rewrite_cfg *init_copy_notes_for_rewrite(const char *cmd);
 int copy_note_for_rewrite(struct notes_rewrite_cfg *c,
-			  const unsigned char *from_obj, const unsigned char *to_obj);
+			  const struct object_id *from_obj, const struct object_id *to_obj);
 void finish_copy_notes_for_rewrite(struct notes_rewrite_cfg *c, const char *msg);
 
 #endif
diff --git a/notes.c b/notes.c
index 542563b280..4b3a1adda5 100644
--- a/notes.c
+++ b/notes.c
@@ -35,8 +35,8 @@ struct int_node {
  * subtree.
  */
 struct leaf_node {
-	unsigned char key_sha1[20];
-	unsigned char val_sha1[20];
+	struct object_id key_oid;
+	struct object_id val_oid;
 };
 
 /*
@@ -51,7 +51,7 @@ struct non_note {
 	struct non_note *next; /* grounded (last->next == NULL) */
 	char *path;
 	unsigned int mode;
-	unsigned char sha1[20];
+	struct object_id oid;
 };
 
 #define PTR_TYPE_NULL     0
@@ -65,8 +65,10 @@ struct non_note {
 
 #define GET_NIBBLE(n, sha1) (((sha1[(n) >> 1]) >> ((~(n) & 0x01) << 2)) & 0x0f)
 
+#define KEY_INDEX (GIT_SHA1_RAWSZ - 1)
+#define FANOUT_PATH_SEPARATORS ((GIT_SHA1_HEXSZ / 2) - 1)
 #define SUBTREE_SHA1_PREFIXCMP(key_sha1, subtree_sha1) \
-	(memcmp(key_sha1, subtree_sha1, subtree_sha1[19]))
+	(memcmp(key_sha1, subtree_sha1, subtree_sha1[KEY_INDEX]))
 
 struct notes_tree default_notes_tree;
 
@@ -100,7 +102,7 @@ static void **note_tree_search(struct notes_tree *t, struct int_node **tree,
 
 	if (GET_PTR_TYPE(p) == PTR_TYPE_SUBTREE) {
 		l = (struct leaf_node *) CLR_PTR_TYPE(p);
-		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
+		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_oid.hash)) {
 			/* unpack tree and resume search */
 			(*tree)->a[0] = NULL;
 			load_subtree(t, l, *tree, *n);
@@ -118,7 +120,7 @@ static void **note_tree_search(struct notes_tree *t, struct int_node **tree,
 		return note_tree_search(t, tree, n, key_sha1);
 	case PTR_TYPE_SUBTREE:
 		l = (struct leaf_node *) CLR_PTR_TYPE(p);
-		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
+		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_oid.hash)) {
 			/* unpack tree and resume search */
 			(*tree)->a[i] = NULL;
 			load_subtree(t, l, *tree, *n);
@@ -143,7 +145,7 @@ static struct leaf_node *note_tree_find(struct notes_tree *t,
 	void **p = note_tree_search(t, &tree, &n, key_sha1);
 	if (GET_PTR_TYPE(*p) == PTR_TYPE_NOTE) {
 		struct leaf_node *l = (struct leaf_node *) CLR_PTR_TYPE(*p);
-		if (!hashcmp(key_sha1, l->key_sha1))
+		if (!hashcmp(key_sha1, l->key_oid.hash))
 			return l;
 	}
 	return NULL;
@@ -194,19 +196,19 @@ static void note_tree_remove(struct notes_tree *t,
 		struct leaf_node *entry)
 {
 	struct leaf_node *l;
-	struct int_node *parent_stack[20];
+	struct int_node *parent_stack[GIT_SHA1_RAWSZ];
 	unsigned char i, j;
-	void **p = note_tree_search(t, &tree, &n, entry->key_sha1);
+	void **p = note_tree_search(t, &tree, &n, entry->key_oid.hash);
 
 	assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
 	if (GET_PTR_TYPE(*p) != PTR_TYPE_NOTE)
 		return; /* type mismatch, nothing to remove */
 	l = (struct leaf_node *) CLR_PTR_TYPE(*p);
-	if (hashcmp(l->key_sha1, entry->key_sha1))
+	if (oidcmp(&l->key_oid, &entry->key_oid))
 		return; /* key mismatch, nothing to remove */
 
 	/* we have found a matching entry */
-	hashcpy(entry->val_sha1, l->val_sha1);
+	oidcpy(&entry->val_oid, &l->val_oid);
 	free(l);
 	*p = SET_PTR_TYPE(NULL, PTR_TYPE_NULL);
 
@@ -216,14 +218,14 @@ static void note_tree_remove(struct notes_tree *t,
 	/* first, build stack of ancestors between root and current node */
 	parent_stack[0] = t->root;
 	for (i = 0; i < n; i++) {
-		j = GET_NIBBLE(i, entry->key_sha1);
+		j = GET_NIBBLE(i, entry->key_oid.hash);
 		parent_stack[i + 1] = CLR_PTR_TYPE(parent_stack[i]->a[j]);
 	}
 	assert(i == n && parent_stack[i] == tree);
 	/* next, unwind stack until note_tree_consolidate() is done */
 	while (i > 0 &&
 	       !note_tree_consolidate(parent_stack[i], parent_stack[i - 1],
-				      GET_NIBBLE(i - 1, entry->key_sha1)))
+				      GET_NIBBLE(i - 1, entry->key_oid.hash)))
 		i--;
 }
 
@@ -246,7 +248,7 @@ static int note_tree_insert(struct notes_tree *t, struct int_node *tree,
 {
 	struct int_node *new_node;
 	struct leaf_node *l;
-	void **p = note_tree_search(t, &tree, &n, entry->key_sha1);
+	void **p = note_tree_search(t, &tree, &n, entry->key_oid.hash);
 	int ret = 0;
 
 	assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
@@ -254,7 +256,7 @@ static int note_tree_insert(struct notes_tree *t, struct int_node *tree,
 	switch (GET_PTR_TYPE(*p)) {
 	case PTR_TYPE_NULL:
 		assert(!*p);
-		if (is_null_sha1(entry->val_sha1))
+		if (is_null_oid(&entry->val_oid))
 			free(entry);
 		else
 			*p = SET_PTR_TYPE(entry, type);
@@ -262,22 +264,22 @@ static int note_tree_insert(struct notes_tree *t, struct int_node *tree,
 	case PTR_TYPE_NOTE:
 		switch (type) {
 		case PTR_TYPE_NOTE:
-			if (!hashcmp(l->key_sha1, entry->key_sha1)) {
+			if (!oidcmp(&l->key_oid, &entry->key_oid)) {
 				/* skip concatenation if l == entry */
-				if (!hashcmp(l->val_sha1, entry->val_sha1))
+				if (!oidcmp(&l->val_oid, &entry->val_oid))
 					return 0;
 
-				ret = combine_notes(l->val_sha1,
-						    entry->val_sha1);
-				if (!ret && is_null_sha1(l->val_sha1))
+				ret = combine_notes(l->val_oid.hash,
+						    entry->val_oid.hash);
+				if (!ret && is_null_oid(&l->val_oid))
 					note_tree_remove(t, tree, n, entry);
 				free(entry);
 				return ret;
 			}
 			break;
 		case PTR_TYPE_SUBTREE:
-			if (!SUBTREE_SHA1_PREFIXCMP(l->key_sha1,
-						    entry->key_sha1)) {
+			if (!SUBTREE_SHA1_PREFIXCMP(l->key_oid.hash,
+						    entry->key_oid.hash)) {
 				/* unpack 'entry' */
 				load_subtree(t, entry, tree, n);
 				free(entry);
@@ -287,7 +289,7 @@ static int note_tree_insert(struct notes_tree *t, struct int_node *tree,
 		}
 		break;
 	case PTR_TYPE_SUBTREE:
-		if (!SUBTREE_SHA1_PREFIXCMP(entry->key_sha1, l->key_sha1)) {
+		if (!SUBTREE_SHA1_PREFIXCMP(entry->key_oid.hash, l->key_oid.hash)) {
 			/* unpack 'l' and restart insert */
 			*p = NULL;
 			load_subtree(t, l, tree, n);
@@ -301,7 +303,7 @@ static int note_tree_insert(struct notes_tree *t, struct int_node *tree,
 	/* non-matching leaf_node */
 	assert(GET_PTR_TYPE(*p) == PTR_TYPE_NOTE ||
 	       GET_PTR_TYPE(*p) == PTR_TYPE_SUBTREE);
-	if (is_null_sha1(entry->val_sha1)) { /* skip insertion of empty note */
+	if (is_null_oid(&entry->val_oid)) { /* skip insertion of empty note */
 		free(entry);
 		return 0;
 	}
@@ -341,21 +343,21 @@ static void note_tree_free(struct int_node *tree)
  * Otherwise, returns number of bytes written to sha1 (i.e. hex_len / 2).
  * Pads sha1 with NULs up to sha1_len (not included in returned length).
  */
-static int get_sha1_hex_segment(const char *hex, unsigned int hex_len,
-		unsigned char *sha1, unsigned int sha1_len)
+static int get_oid_hex_segment(const char *hex, unsigned int hex_len,
+		unsigned char *oid, unsigned int oid_len)
 {
 	unsigned int i, len = hex_len >> 1;
-	if (hex_len % 2 != 0 || len > sha1_len)
+	if (hex_len % 2 != 0 || len > oid_len)
 		return -1;
 	for (i = 0; i < len; i++) {
 		unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
 		if (val & ~0xff)
 			return -1;
-		*sha1++ = val;
+		*oid++ = val;
 		hex += 2;
 	}
-	for (; i < sha1_len; i++)
-		*sha1++ = 0;
+	for (; i < oid_len; i++)
+		*oid++ = 0;
 	return len;
 }
 
@@ -373,7 +375,7 @@ static void add_non_note(struct notes_tree *t, char *path,
 	n->next = NULL;
 	n->path = path;
 	n->mode = mode;
-	hashcpy(n->sha1, sha1);
+	hashcpy(n->oid.hash, sha1);
 	t->prev_non_note = n;
 
 	if (!t->first_non_note) {
@@ -399,7 +401,7 @@ static void add_non_note(struct notes_tree *t, char *path,
 	if (non_note_cmp(p, n) == 0) { /* n ~= p; overwrite p with n */
 		assert(strcmp(p->path, n->path) == 0);
 		p->mode = n->mode;
-		hashcpy(p->sha1, n->sha1);
+		oidcpy(&p->oid, &n->oid);
 		free(n);
 		t->prev_non_note = p;
 		return;
@@ -413,7 +415,7 @@ static void add_non_note(struct notes_tree *t, char *path,
 static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
 		struct int_node *node, unsigned int n)
 {
-	unsigned char object_sha1[20];
+	struct object_id object_oid;
 	unsigned int prefix_len;
 	void *buf;
 	struct tree_desc desc;
@@ -422,18 +424,18 @@ static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
 	unsigned char type;
 	struct leaf_node *l;
 
-	buf = fill_tree_descriptor(&desc, subtree->val_sha1);
+	buf = fill_tree_descriptor(&desc, subtree->val_oid.hash);
 	if (!buf)
 		die("Could not read %s for notes-index",
-		     sha1_to_hex(subtree->val_sha1));
+		     oid_to_hex(&subtree->val_oid));
 
-	prefix_len = subtree->key_sha1[19];
+	prefix_len = subtree->key_oid.hash[KEY_INDEX];
 	assert(prefix_len * 2 >= n);
-	memcpy(object_sha1, subtree->key_sha1, prefix_len);
+	memcpy(object_oid.hash, subtree->key_oid.hash, prefix_len);
 	while (tree_entry(&desc, &entry)) {
 		path_len = strlen(entry.path);
-		len = get_sha1_hex_segment(entry.path, path_len,
-				object_sha1 + prefix_len, 20 - prefix_len);
+		len = get_oid_hex_segment(entry.path, path_len,
+				object_oid.hash + prefix_len, GIT_SHA1_RAWSZ - prefix_len);
 		if (len < 0)
 			goto handle_non_note; /* entry.path is not a SHA1 */
 		len += prefix_len;
@@ -443,16 +445,16 @@ static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
 		 * If object SHA1 is incomplete (len < 20), and current
 		 * component consists of 2 hex chars, assume note subtree
 		 */
-		if (len <= 20) {
+		if (len <= GIT_SHA1_RAWSZ) {
 			type = PTR_TYPE_NOTE;
 			l = (struct leaf_node *)
 				xcalloc(1, sizeof(struct leaf_node));
-			hashcpy(l->key_sha1, object_sha1);
-			hashcpy(l->val_sha1, entry.oid->hash);
-			if (len < 20) {
+			oidcpy(&l->key_oid, &object_oid);
+			oidcpy(&l->val_oid, entry.oid);
+			if (len < GIT_SHA1_RAWSZ) {
 				if (!S_ISDIR(entry.mode) || path_len != 2)
 					goto handle_non_note; /* not subtree */
-				l->key_sha1[19] = (unsigned char) len;
+				l->key_oid.hash[KEY_INDEX] = (unsigned char) len;
 				type = PTR_TYPE_SUBTREE;
 			}
 			if (note_tree_insert(t, node, n, l, type,
@@ -460,7 +462,7 @@ static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
 				die("Failed to load %s %s into notes tree "
 				    "from %s",
 				    type == PTR_TYPE_NOTE ? "note" : "subtree",
-				    sha1_to_hex(l->key_sha1), t->ref);
+				    oid_to_hex(&l->key_oid), t->ref);
 		}
 		continue;
 
@@ -486,7 +488,7 @@ handle_non_note:
 		 */
 		{
 			struct strbuf non_note_path = STRBUF_INIT;
-			const char *q = sha1_to_hex(subtree->key_sha1);
+			const char *q = oid_to_hex(&subtree->key_oid);
 			int i;
 			for (i = 0; i < prefix_len; i++) {
 				strbuf_addch(&non_note_path, *q++);
@@ -542,14 +544,14 @@ static unsigned char determine_fanout(struct int_node *tree, unsigned char n,
 }
 
 /* hex SHA1 + 19 * '/' + NUL */
-#define FANOUT_PATH_MAX 40 + 19 + 1
+#define FANOUT_PATH_MAX GIT_SHA1_HEXSZ + FANOUT_PATH_SEPARATORS + 1
 
 static void construct_path_with_fanout(const unsigned char *sha1,
 		unsigned char fanout, char *path)
 {
 	unsigned int i = 0, j = 0;
 	const char *hex_sha1 = sha1_to_hex(sha1);
-	assert(fanout < 20);
+	assert(fanout < GIT_SHA1_RAWSZ);
 	while (fanout) {
 		path[i++] = hex_sha1[j++];
 		path[i++] = hex_sha1[j++];
@@ -599,15 +601,17 @@ redo:
 			    flags & FOR_EACH_NOTE_YIELD_SUBTREES) {
 				/* invoke callback with subtree */
 				unsigned int path_len =
-					l->key_sha1[19] * 2 + fanout;
+					l->key_oid.hash[KEY_INDEX] * 2 + fanout;
 				assert(path_len < FANOUT_PATH_MAX - 1);
-				construct_path_with_fanout(l->key_sha1, fanout,
+				construct_path_with_fanout(l->key_oid.hash,
+							   fanout,
 							   path);
 				/* Create trailing slash, if needed */
 				if (path[path_len - 1] != '/')
 					path[path_len++] = '/';
 				path[path_len] = '\0';
-				ret = fn(l->key_sha1, l->val_sha1, path,
+				ret = fn(&l->key_oid, &l->val_oid,
+					 path,
 					 cb_data);
 			}
 			if (n > fanout * 2 ||
@@ -621,8 +625,10 @@ redo:
 			break;
 		case PTR_TYPE_NOTE:
 			l = (struct leaf_node *) CLR_PTR_TYPE(p);
-			construct_path_with_fanout(l->key_sha1, fanout, path);
-			ret = fn(l->key_sha1, l->val_sha1, path, cb_data);
+			construct_path_with_fanout(l->key_oid.hash, fanout,
+						   path);
+			ret = fn(&l->key_oid, &l->val_oid, path,
+				 cb_data);
 			break;
 		}
 		if (ret)
@@ -650,7 +656,7 @@ static void write_tree_entry(struct strbuf *buf, unsigned int mode,
 		unsigned char *sha1)
 {
 	strbuf_addf(buf, "%o %.*s%c", mode, path_len, path, '\0');
-	strbuf_add(buf, sha1, 20);
+	strbuf_add(buf, sha1, GIT_SHA1_RAWSZ);
 }
 
 static void tree_write_stack_init_subtree(struct tree_write_stack *tws,
@@ -662,7 +668,7 @@ static void tree_write_stack_init_subtree(struct tree_write_stack *tws,
 	n = (struct tree_write_stack *)
 		xmalloc(sizeof(struct tree_write_stack));
 	n->next = NULL;
-	strbuf_init(&n->buf, 256 * (32 + 40)); /* assume 256 entries per tree */
+	strbuf_init(&n->buf, 256 * (32 + GIT_SHA1_HEXSZ)); /* assume 256 entries per tree */
 	n->path[0] = n->path[1] = '\0';
 	tws->next = n;
 	tws->path[0] = path[0];
@@ -673,18 +679,18 @@ static int tree_write_stack_finish_subtree(struct tree_write_stack *tws)
 {
 	int ret;
 	struct tree_write_stack *n = tws->next;
-	unsigned char s[20];
+	struct object_id s;
 	if (n) {
 		ret = tree_write_stack_finish_subtree(n);
 		if (ret)
 			return ret;
-		ret = write_sha1_file(n->buf.buf, n->buf.len, tree_type, s);
+		ret = write_sha1_file(n->buf.buf, n->buf.len, tree_type, s.hash);
 		if (ret)
 			return ret;
 		strbuf_release(&n->buf);
 		free(n);
 		tws->next = NULL;
-		write_tree_entry(&tws->buf, 040000, tws->path, 2, s);
+		write_tree_entry(&tws->buf, 040000, tws->path, 2, s.hash);
 		tws->path[0] = tws->path[1] = '\0';
 	}
 	return 0;
@@ -692,7 +698,7 @@ static int tree_write_stack_finish_subtree(struct tree_write_stack *tws)
 
 static int write_each_note_helper(struct tree_write_stack *tws,
 		const char *path, unsigned int mode,
-		const unsigned char *sha1)
+		const struct object_id *oid)
 {
 	size_t path_len = strlen(path);
 	unsigned int n = 0;
@@ -722,7 +728,7 @@ static int write_each_note_helper(struct tree_write_stack *tws,
 
 	/* Finally add given entry to the current tree object */
 	write_tree_entry(&tws->buf, mode, path + 3 * n, path_len - (3 * n),
-			 sha1);
+			 oid->hash);
 
 	return 0;
 }
@@ -742,7 +748,7 @@ static int write_each_non_note_until(const char *note_path,
 			; /* do nothing, prefer note to non-note */
 		else {
 			ret = write_each_note_helper(d->root, n->path, n->mode,
-						     n->sha1);
+						     &n->oid);
 			if (ret)
 				return ret;
 		}
@@ -752,8 +758,8 @@ static int write_each_non_note_until(const char *note_path,
 	return 0;
 }
 
-static int write_each_note(const unsigned char *object_sha1,
-		const unsigned char *note_sha1, char *note_path,
+static int write_each_note(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
 		void *cb_data)
 {
 	struct write_each_note_data *d =
@@ -767,11 +773,11 @@ static int write_each_note(const unsigned char *object_sha1,
 		note_path[note_path_len] = '\0';
 		mode = 040000;
 	}
-	assert(note_path_len <= 40 + 19);
+	assert(note_path_len <= GIT_SHA1_HEXSZ + FANOUT_PATH_SEPARATORS);
 
 	/* Weave non-note entries into note entries */
 	return  write_each_non_note_until(note_path, d) ||
-		write_each_note_helper(d->root, note_path, mode, note_sha1);
+		write_each_note_helper(d->root, note_path, mode, note_oid);
 }
 
 struct note_delete_list {
@@ -779,20 +785,20 @@ struct note_delete_list {
 	const unsigned char *sha1;
 };
 
-static int prune_notes_helper(const unsigned char *object_sha1,
-		const unsigned char *note_sha1, char *note_path,
+static int prune_notes_helper(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
 		void *cb_data)
 {
 	struct note_delete_list **l = (struct note_delete_list **) cb_data;
 	struct note_delete_list *n;
 
-	if (has_sha1_file(object_sha1))
+	if (has_object_file(object_oid))
 		return 0; /* nothing to do for this note */
 
 	/* failed to find object => prune this note */
 	n = (struct note_delete_list *) xmalloc(sizeof(*n));
 	n->next = *l;
-	n->sha1 = object_sha1;
+	n->sha1 = object_oid->hash;
 	*l = n;
 	return 0;
 }
@@ -942,8 +948,8 @@ void string_list_add_refs_by_glob(struct string_list *list, const char *glob)
 	if (has_glob_specials(glob)) {
 		for_each_glob_ref(string_list_add_one_ref, glob, list);
 	} else {
-		unsigned char sha1[20];
-		if (get_sha1(glob, sha1))
+		struct object_id oid;
+		if (get_oid(glob, &oid))
 			warning("notes ref %s is invalid", glob);
 		if (!unsorted_string_list_has_string(list, glob))
 			string_list_append(list, glob);
@@ -1027,8 +1033,8 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
 		die("Failed to read notes tree referenced by %s (%s)",
 		    notes_ref, oid_to_hex(&object_oid));
 
-	hashclr(root_tree.key_sha1);
-	hashcpy(root_tree.val_sha1, oid.hash);
+	oidclr(&root_tree.key_oid);
+	oidcpy(&root_tree.val_oid, &oid);
 	load_subtree(t, &root_tree, t->root, 0);
 }
 
@@ -1080,8 +1086,8 @@ void init_display_notes(struct display_notes_opt *opt)
 	string_list_clear(&display_notes_refs, 0);
 }
 
-int add_note(struct notes_tree *t, const unsigned char *object_sha1,
-		const unsigned char *note_sha1, combine_notes_fn combine_notes)
+int add_note(struct notes_tree *t, const struct object_id *object_oid,
+		const struct object_id *note_oid, combine_notes_fn combine_notes)
 {
 	struct leaf_node *l;
 
@@ -1092,8 +1098,8 @@ int add_note(struct notes_tree *t, const unsigned char *object_sha1,
 	if (!combine_notes)
 		combine_notes = t->combine_notes;
 	l = (struct leaf_node *) xmalloc(sizeof(struct leaf_node));
-	hashcpy(l->key_sha1, object_sha1);
-	hashcpy(l->val_sha1, note_sha1);
+	oidcpy(&l->key_oid, object_oid);
+	oidcpy(&l->val_oid, note_oid);
 	return note_tree_insert(t, t->root, 0, l, PTR_TYPE_NOTE, combine_notes);
 }
 
@@ -1104,25 +1110,25 @@ int remove_note(struct notes_tree *t, const unsigned char *object_sha1)
 	if (!t)
 		t = &default_notes_tree;
 	assert(t->initialized);
-	hashcpy(l.key_sha1, object_sha1);
-	hashclr(l.val_sha1);
+	hashcpy(l.key_oid.hash, object_sha1);
+	oidclr(&l.val_oid);
 	note_tree_remove(t, t->root, 0, &l);
-	if (is_null_sha1(l.val_sha1)) /* no note was removed */
+	if (is_null_oid(&l.val_oid)) /* no note was removed */
 		return 1;
 	t->dirty = 1;
 	return 0;
 }
 
-const unsigned char *get_note(struct notes_tree *t,
-		const unsigned char *object_sha1)
+const struct object_id *get_note(struct notes_tree *t,
+		const struct object_id *oid)
 {
 	struct leaf_node *found;
 
 	if (!t)
 		t = &default_notes_tree;
 	assert(t->initialized);
-	found = note_tree_find(t, t->root, 0, object_sha1);
-	return found ? found->val_sha1 : NULL;
+	found = note_tree_find(t, t->root, 0, oid->hash);
+	return found ? &found->val_oid : NULL;
 }
 
 int for_each_note(struct notes_tree *t, int flags, each_note_fn fn,
@@ -1146,7 +1152,7 @@ int write_notes_tree(struct notes_tree *t, unsigned char *result)
 
 	/* Prepare for traversal of current notes tree */
 	root.next = NULL; /* last forward entry in list is grounded */
-	strbuf_init(&root.buf, 256 * (32 + 40)); /* assume 256 entries */
+	strbuf_init(&root.buf, 256 * (32 + GIT_SHA1_HEXSZ)); /* assume 256 entries */
 	root.path[0] = root.path[1] = '\0';
 	cb_data.root = &root;
 	cb_data.next_non_note = t->first_non_note;
@@ -1209,11 +1215,11 @@ void free_notes(struct notes_tree *t)
  * (raw != 0) gives the %N userformat; otherwise, the note message is given
  * for human consumption.
  */
-static void format_note(struct notes_tree *t, const unsigned char *object_sha1,
+static void format_note(struct notes_tree *t, const struct object_id *object_oid,
 			struct strbuf *sb, const char *output_encoding, int raw)
 {
 	static const char utf8[] = "utf-8";
-	const unsigned char *sha1;
+	const struct object_id *oid;
 	char *msg, *msg_p;
 	unsigned long linelen, msglen;
 	enum object_type type;
@@ -1223,11 +1229,11 @@ static void format_note(struct notes_tree *t, const unsigned char *object_sha1,
 	if (!t->initialized)
 		init_notes(t, NULL, NULL, 0);
 
-	sha1 = get_note(t, object_sha1);
-	if (!sha1)
+	oid = get_note(t, object_oid);
+	if (!oid)
 		return;
 
-	if (!(msg = read_sha1_file(sha1, &type, &msglen)) || type != OBJ_BLOB) {
+	if (!(msg = read_sha1_file(oid->hash, &type, &msglen)) || type != OBJ_BLOB) {
 		free(msg);
 		return;
 	}
@@ -1271,22 +1277,22 @@ static void format_note(struct notes_tree *t, const unsigned char *object_sha1,
 	free(msg);
 }
 
-void format_display_notes(const unsigned char *object_sha1,
+void format_display_notes(const struct object_id *object_oid,
 			  struct strbuf *sb, const char *output_encoding, int raw)
 {
 	int i;
 	assert(display_notes_trees);
 	for (i = 0; display_notes_trees[i]; i++)
-		format_note(display_notes_trees[i], object_sha1, sb,
+		format_note(display_notes_trees[i], object_oid, sb,
 			    output_encoding, raw);
 }
 
 int copy_note(struct notes_tree *t,
-	      const unsigned char *from_obj, const unsigned char *to_obj,
+	      const struct object_id *from_obj, const struct object_id *to_obj,
 	      int force, combine_notes_fn combine_notes)
 {
-	const unsigned char *note = get_note(t, from_obj);
-	const unsigned char *existing_note = get_note(t, to_obj);
+	const struct object_id *note = get_note(t, from_obj);
+	const struct object_id *existing_note = get_note(t, to_obj);
 
 	if (!force && existing_note)
 		return 1;
@@ -1294,7 +1300,7 @@ int copy_note(struct notes_tree *t,
 	if (note)
 		return add_note(t, to_obj, note, combine_notes);
 	else if (existing_note)
-		return add_note(t, to_obj, null_sha1, combine_notes);
+		return add_note(t, to_obj, &null_oid, combine_notes);
 
 	return 0;
 }
@@ -1311,9 +1317,9 @@ void expand_notes_ref(struct strbuf *sb)
 
 void expand_loose_notes_ref(struct strbuf *sb)
 {
-	unsigned char object[20];
+	struct object_id object;
 
-	if (get_sha1(sb->buf, object)) {
+	if (get_oid(sb->buf, &object)) {
 		/* fallback to expand_notes_ref */
 		expand_notes_ref(sb);
 	}
diff --git a/notes.h b/notes.h
index 5345642cfd..3848c2fb3f 100644
--- a/notes.h
+++ b/notes.h
@@ -121,8 +121,8 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
  * are not persistent until a subsequent call to write_notes_tree() returns
  * zero.
  */
-int add_note(struct notes_tree *t, const unsigned char *object_sha1,
-		const unsigned char *note_sha1, combine_notes_fn combine_notes);
+int add_note(struct notes_tree *t, const struct object_id *object_oid,
+		const struct object_id *note_oid, combine_notes_fn combine_notes);
 
 /*
  * Remove the given note object from the given notes_tree structure
@@ -140,8 +140,8 @@ int remove_note(struct notes_tree *t, const unsigned char *object_sha1);
  *
  * Return NULL if the given object has no notes.
  */
-const unsigned char *get_note(struct notes_tree *t,
-		const unsigned char *object_sha1);
+const struct object_id *get_note(struct notes_tree *t,
+		const struct object_id *object_oid);
 
 /*
  * Copy a note from one object to another in the given notes_tree.
@@ -156,7 +156,7 @@ const unsigned char *get_note(struct notes_tree *t,
  * zero.
  */
 int copy_note(struct notes_tree *t,
-	      const unsigned char *from_obj, const unsigned char *to_obj,
+	      const struct object_id *from_obj, const struct object_id *to_obj,
 	      int force, combine_notes_fn combine_notes);
 
 /*
@@ -202,8 +202,8 @@ int copy_note(struct notes_tree *t,
  * - copy_note()
  * - free_notes()
  */
-typedef int each_note_fn(const unsigned char *object_sha1,
-		const unsigned char *note_sha1, char *note_path,
+typedef int each_note_fn(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
 		void *cb_data);
 int for_each_note(struct notes_tree *t, int flags, each_note_fn fn,
 		void *cb_data);
@@ -277,7 +277,7 @@ void init_display_notes(struct display_notes_opt *opt);
  *
  * You *must* call init_display_notes() before using this function.
  */
-void format_display_notes(const unsigned char *object_sha1,
+void format_display_notes(const struct object_id *object_oid,
 			  struct strbuf *sb, const char *output_encoding, int raw);
 
 /*
diff --git a/patch-ids.c b/patch-ids.c
index 92eba7a059..9c0ab9e67a 100644
--- a/patch-ids.c
+++ b/patch-ids.c
@@ -11,18 +11,18 @@ static int patch_id_defined(struct commit *commit)
 }
 
 int commit_patch_id(struct commit *commit, struct diff_options *options,
-		    unsigned char *sha1, int diff_header_only)
+		    struct object_id *oid, int diff_header_only)
 {
 	if (!patch_id_defined(commit))
 		return -1;
 
 	if (commit->parents)
-		diff_tree_sha1(commit->parents->item->object.oid.hash,
-			       commit->object.oid.hash, "", options);
+		diff_tree_oid(&commit->parents->item->object.oid,
+			      &commit->object.oid, "", options);
 	else
-		diff_root_tree_sha1(commit->object.oid.hash, "", options);
+		diff_root_tree_oid(&commit->object.oid, "", options);
 	diffcore_std(options);
-	return diff_flush_patch_id(options, sha1, diff_header_only);
+	return diff_flush_patch_id(options, oid, diff_header_only);
 }
 
 /*
@@ -39,15 +39,15 @@ static int patch_id_cmp(struct patch_id *a,
 			struct patch_id *b,
 			struct diff_options *opt)
 {
-	if (is_null_sha1(a->patch_id) &&
-	    commit_patch_id(a->commit, opt, a->patch_id, 0))
+	if (is_null_oid(&a->patch_id) &&
+	    commit_patch_id(a->commit, opt, &a->patch_id, 0))
 		return error("Could not get patch ID for %s",
 			oid_to_hex(&a->commit->object.oid));
-	if (is_null_sha1(b->patch_id) &&
-	    commit_patch_id(b->commit, opt, b->patch_id, 0))
+	if (is_null_oid(&b->patch_id) &&
+	    commit_patch_id(b->commit, opt, &b->patch_id, 0))
 		return error("Could not get patch ID for %s",
 			oid_to_hex(&b->commit->object.oid));
-	return hashcmp(a->patch_id, b->patch_id);
+	return oidcmp(&a->patch_id, &b->patch_id);
 }
 
 int init_patch_ids(struct patch_ids *ids)
@@ -71,13 +71,13 @@ static int init_patch_id_entry(struct patch_id *patch,
 			       struct commit *commit,
 			       struct patch_ids *ids)
 {
-	unsigned char header_only_patch_id[GIT_MAX_RAWSZ];
+	struct object_id header_only_patch_id;
 
 	patch->commit = commit;
-	if (commit_patch_id(commit, &ids->diffopts, header_only_patch_id, 1))
+	if (commit_patch_id(commit, &ids->diffopts, &header_only_patch_id, 1))
 		return -1;
 
-	hashmap_entry_init(patch, sha1hash(header_only_patch_id));
+	hashmap_entry_init(patch, sha1hash(header_only_patch_id.hash));
 	return 0;
 }
 
diff --git a/patch-ids.h b/patch-ids.h
index b9e5751f8e..bec0f727a7 100644
--- a/patch-ids.h
+++ b/patch-ids.h
@@ -3,7 +3,7 @@
 
 struct patch_id {
 	struct hashmap_entry ent;
-	unsigned char patch_id[GIT_MAX_RAWSZ];
+	struct object_id patch_id;
 	struct commit *commit;
 };
 
@@ -13,7 +13,7 @@ struct patch_ids {
 };
 
 int commit_patch_id(struct commit *commit, struct diff_options *options,
-		    unsigned char *sha1, int);
+		    struct object_id *oid, int);
 int init_patch_ids(struct patch_ids *);
 int free_patch_ids(struct patch_ids *);
 struct patch_id *add_commit_patch_id(struct commit *, struct patch_ids *);
diff --git a/remote-testsvn.c b/remote-testsvn.c
index 50404ef343..e034ea00d4 100644
--- a/remote-testsvn.c
+++ b/remote-testsvn.c
@@ -51,17 +51,17 @@ static void terminate_batch(void)
 }
 
 /* NOTE: 'ref' refers to a git reference, while 'rev' refers to a svn revision. */
-static char *read_ref_note(const unsigned char sha1[20])
+static char *read_ref_note(const struct object_id *oid)
 {
-	const unsigned char *note_sha1;
+	const struct object_id *note_oid;
 	char *msg = NULL;
 	unsigned long msglen;
 	enum object_type type;
 
 	init_notes(NULL, notes_ref, NULL, 0);
-	if (!(note_sha1 = get_note(NULL, sha1)))
+	if (!(note_oid = get_note(NULL, oid)))
 		return NULL;	/* note tree not found */
-	if (!(msg = read_sha1_file(note_sha1, &type, &msglen)))
+	if (!(msg = read_sha1_file(note_oid->hash, &type, &msglen)))
 		error("Empty notes tree. %s", notes_ref);
 	else if (!msglen || type != OBJ_BLOB) {
 		error("Note contains unusable content. "
@@ -99,8 +99,8 @@ static int parse_rev_note(const char *msg, struct rev_note *res)
 	return -1;
 }
 
-static int note2mark_cb(const unsigned char *object_sha1,
-		const unsigned char *note_sha1, char *note_path,
+static int note2mark_cb(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
 		void *cb_data)
 {
 	FILE *file = (FILE *)cb_data;
@@ -109,14 +109,14 @@ static int note2mark_cb(const unsigned char *object_sha1,
 	enum object_type type;
 	struct rev_note note;
 
-	if (!(msg = read_sha1_file(note_sha1, &type, &msglen)) ||
+	if (!(msg = read_sha1_file(note_oid->hash, &type, &msglen)) ||
 			!msglen || type != OBJ_BLOB) {
 		free(msg);
 		return 1;
 	}
 	if (parse_rev_note(msg, &note))
 		return 2;
-	if (fprintf(file, ":%d %s\n", note.rev_nr, sha1_to_hex(object_sha1)) < 1)
+	if (fprintf(file, ":%d %s\n", note.rev_nr, oid_to_hex(object_oid)) < 1)
 		return 3;
 	return 0;
 }
@@ -170,15 +170,15 @@ static int cmd_import(const char *line)
 	int code;
 	int dumpin_fd;
 	char *note_msg;
-	unsigned char head_sha1[20];
+	struct object_id head_oid;
 	unsigned int startrev;
 	struct child_process svndump_proc = CHILD_PROCESS_INIT;
 	const char *command = "svnrdump";
 
-	if (read_ref(private_ref, head_sha1))
+	if (read_ref(private_ref, head_oid.hash))
 		startrev = 0;
 	else {
-		note_msg = read_ref_note(head_sha1);
+		note_msg = read_ref_note(&head_oid);
 		if(note_msg == NULL) {
 			warning("No note found for %s.", private_ref);
 			startrev = 0;
diff --git a/revision.c b/revision.c
index 3b09cd6ee9..12eb332350 100644
--- a/revision.c
+++ b/revision.c
@@ -401,8 +401,8 @@ static int tree_difference = REV_TREE_SAME;
 
 static void file_add_remove(struct diff_options *options,
 		    int addremove, unsigned mode,
-		    const unsigned char *sha1,
-		    int sha1_valid,
+		    const struct object_id *oid,
+		    int oid_valid,
 		    const char *fullpath, unsigned dirty_submodule)
 {
 	int diff = addremove == '+' ? REV_TREE_NEW : REV_TREE_OLD;
@@ -414,9 +414,9 @@ static void file_add_remove(struct diff_options *options,
 
 static void file_change(struct diff_options *options,
 		 unsigned old_mode, unsigned new_mode,
-		 const unsigned char *old_sha1,
-		 const unsigned char *new_sha1,
-		 int old_sha1_valid, int new_sha1_valid,
+		 const struct object_id *old_oid,
+		 const struct object_id *new_oid,
+		 int old_oid_valid, int new_oid_valid,
 		 const char *fullpath,
 		 unsigned old_dirty_submodule, unsigned new_dirty_submodule)
 {
@@ -455,7 +455,7 @@ static int rev_compare_tree(struct rev_info *revs,
 
 	tree_difference = REV_TREE_SAME;
 	DIFF_OPT_CLR(&revs->pruning, HAS_CHANGES);
-	if (diff_tree_sha1(t1->object.oid.hash, t2->object.oid.hash, "",
+	if (diff_tree_oid(&t1->object.oid, &t2->object.oid, "",
 			   &revs->pruning) < 0)
 		return REV_TREE_DIFFERENT;
 	return tree_difference;
@@ -471,7 +471,7 @@ static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
 
 	tree_difference = REV_TREE_SAME;
 	DIFF_OPT_CLR(&revs->pruning, HAS_CHANGES);
-	retval = diff_tree_sha1(NULL, t1->object.oid.hash, "", &revs->pruning);
+	retval = diff_tree_oid(NULL, &t1->object.oid, "", &revs->pruning);
 
 	return retval >= 0 && (tree_difference == REV_TREE_SAME);
 }
@@ -2944,7 +2944,7 @@ static int commit_match(struct commit *commit, struct rev_info *opt)
 	if (opt->show_notes) {
 		if (!buf.len)
 			strbuf_addstr(&buf, message);
-		format_display_notes(commit->object.oid.hash, &buf, encoding, 1);
+		format_display_notes(&commit->object.oid, &buf, encoding, 1);
 	}
 
 	/*
diff --git a/sequencer.c b/sequencer.c
index 5282fb849c..d63099d50f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2130,8 +2130,8 @@ cleanup_head_ref:
 			if (read_oneliner(&buf, rebase_path_orig_head(), 0) &&
 			    !get_sha1(buf.buf, orig.hash) &&
 			    !get_sha1("HEAD", head.hash)) {
-				diff_tree_sha1(orig.hash, head.hash,
-					       "", &log_tree_opt.diffopt);
+				diff_tree_oid(&orig, &head, "",
+					      &log_tree_opt.diffopt);
 				log_tree_diff_flush(&log_tree_opt);
 			}
 		}
diff --git a/tree-diff.c b/tree-diff.c
index e164e532b2..467e381724 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -26,11 +26,12 @@
 } while(0)
 
 static struct combine_diff_path *ll_diff_tree_paths(
-	struct combine_diff_path *p, const unsigned char *sha1,
-	const unsigned char **parents_sha1, int nparent,
+	struct combine_diff_path *p, const struct object_id *oid,
+	const struct object_id **parents_oid, int nparent,
 	struct strbuf *base, struct diff_options *opt);
-static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
-			     struct strbuf *base, struct diff_options *opt);
+static int ll_diff_tree_oid(const struct object_id *old_oid,
+			    const struct object_id *new_oid,
+			    struct strbuf *base, struct diff_options *opt);
 
 /*
  * Compare two tree entries, taking into account only path/S_ISDIR(mode),
@@ -74,25 +75,25 @@ static int emit_diff_first_parent_only(struct diff_options *opt, struct combine_
 {
 	struct combine_diff_parent *p0 = &p->parent[0];
 	if (p->mode && p0->mode) {
-		opt->change(opt, p0->mode, p->mode, p0->oid.hash, p->oid.hash,
+		opt->change(opt, p0->mode, p->mode, &p0->oid, &p->oid,
 			1, 1, p->path, 0, 0);
 	}
 	else {
-		const unsigned char *sha1;
+		const struct object_id *oid;
 		unsigned int mode;
 		int addremove;
 
 		if (p->mode) {
 			addremove = '+';
-			sha1 = p->oid.hash;
+			oid = &p->oid;
 			mode = p->mode;
 		} else {
 			addremove = '-';
-			sha1 = p0->oid.hash;
+			oid = &p0->oid;
 			mode = p0->mode;
 		}
 
-		opt->add_remove(opt, addremove, mode, sha1, 1, p->path, 0);
+		opt->add_remove(opt, addremove, mode, oid, 1, p->path, 0);
 	}
 
 	return 0;	/* we are done with p */
@@ -131,7 +132,7 @@ static int emit_diff_first_parent_only(struct diff_options *opt, struct combine_
  */
 static struct combine_diff_path *path_appendnew(struct combine_diff_path *last,
 	int nparent, const struct strbuf *base, const char *path, int pathlen,
-	unsigned mode, const unsigned char *sha1)
+	unsigned mode, const struct object_id *oid)
 {
 	struct combine_diff_path *p;
 	size_t len = st_add(base->len, pathlen);
@@ -161,7 +162,7 @@ static struct combine_diff_path *path_appendnew(struct combine_diff_path *last,
 	memcpy(p->path + base->len, path, pathlen);
 	p->path[len] = 0;
 	p->mode = mode;
-	hashcpy(p->oid.hash, sha1 ? sha1 : null_sha1);
+	oidcpy(&p->oid, oid ? oid : &null_oid);
 
 	return p;
 }
@@ -183,7 +184,7 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 {
 	unsigned mode;
 	const char *path;
-	const unsigned char *sha1;
+	const struct object_id *oid;
 	int pathlen;
 	int old_baselen = base->len;
 	int i, isdir, recurse = 0, emitthis = 1;
@@ -193,7 +194,7 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 
 	if (t) {
 		/* path present in resulting tree */
-		sha1 = tree_entry_extract(t, &path, &mode)->hash;
+		oid = tree_entry_extract(t, &path, &mode);
 		pathlen = tree_entry_len(&t->entry);
 		isdir = S_ISDIR(mode);
 	} else {
@@ -208,7 +209,7 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 		pathlen = tree_entry_len(&tp[imin].entry);
 
 		isdir = S_ISDIR(mode);
-		sha1 = NULL;
+		oid = NULL;
 		mode = 0;
 	}
 
@@ -220,7 +221,7 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 	if (emitthis) {
 		int keep;
 		struct combine_diff_path *pprev = p;
-		p = path_appendnew(p, nparent, base, path, pathlen, mode, sha1);
+		p = path_appendnew(p, nparent, base, path, pathlen, mode, oid);
 
 		for (i = 0; i < nparent; ++i) {
 			/*
@@ -229,7 +230,7 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 			 */
 			int tpi_valid = tp && !(tp[i].entry.mode & S_IFXMIN_NEQ);
 
-			const unsigned char *sha1_i;
+			const struct object_id *oid_i;
 			unsigned mode_i;
 
 			p->parent[i].status =
@@ -239,16 +240,16 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 						DIFF_STATUS_ADDED;
 
 			if (tpi_valid) {
-				sha1_i = tp[i].entry.oid->hash;
+				oid_i = tp[i].entry.oid;
 				mode_i = tp[i].entry.mode;
 			}
 			else {
-				sha1_i = NULL;
+				oid_i = &null_oid;
 				mode_i = 0;
 			}
 
 			p->parent[i].mode = mode_i;
-			hashcpy(p->parent[i].oid.hash, sha1_i ? sha1_i : null_sha1);
+			oidcpy(&p->parent[i].oid, oid_i);
 		}
 
 		keep = 1;
@@ -273,21 +274,20 @@ static struct combine_diff_path *emit_path(struct combine_diff_path *p,
 	}
 
 	if (recurse) {
-		const unsigned char **parents_sha1;
+		const struct object_id **parents_oid;
 
-		FAST_ARRAY_ALLOC(parents_sha1, nparent);
+		FAST_ARRAY_ALLOC(parents_oid, nparent);
 		for (i = 0; i < nparent; ++i) {
 			/* same rule as in emitthis */
 			int tpi_valid = tp && !(tp[i].entry.mode & S_IFXMIN_NEQ);
 
-			parents_sha1[i] = tpi_valid ? tp[i].entry.oid->hash
-						    : NULL;
+			parents_oid[i] = tpi_valid ? tp[i].entry.oid : NULL;
 		}
 
 		strbuf_add(base, path, pathlen);
 		strbuf_addch(base, '/');
-		p = ll_diff_tree_paths(p, sha1, parents_sha1, nparent, base, opt);
-		FAST_ARRAY_FREE(parents_sha1, nparent);
+		p = ll_diff_tree_paths(p, oid, parents_oid, nparent, base, opt);
+		FAST_ARRAY_FREE(parents_oid, nparent);
 	}
 
 	strbuf_setlen(base, old_baselen);
@@ -312,7 +312,7 @@ static void skip_uninteresting(struct tree_desc *t, struct strbuf *base,
 
 
 /*
- * generate paths for combined diff D(sha1,parents_sha1[])
+ * generate paths for combined diff D(sha1,parents_oid[])
  *
  * Resulting paths are appended to combine_diff_path linked list, and also, are
  * emitted on the go via opt->pathchange() callback, so it is possible to
@@ -404,8 +404,8 @@ static inline void update_tp_entries(struct tree_desc *tp, int nparent)
 }
 
 static struct combine_diff_path *ll_diff_tree_paths(
-	struct combine_diff_path *p, const unsigned char *sha1,
-	const unsigned char **parents_sha1, int nparent,
+	struct combine_diff_path *p, const struct object_id *oid,
+	const struct object_id **parents_oid, int nparent,
 	struct strbuf *base, struct diff_options *opt)
 {
 	struct tree_desc t, *tp;
@@ -419,11 +419,11 @@ static struct combine_diff_path *ll_diff_tree_paths(
 	 * load parents first, as they are probably already cached.
 	 *
 	 * ( log_tree_diff() parses commit->parent before calling here via
-	 *   diff_tree_sha1(parent, commit) )
+	 *   diff_tree_oid(parent, commit) )
 	 */
 	for (i = 0; i < nparent; ++i)
-		tptree[i] = fill_tree_descriptor(&tp[i], parents_sha1[i]);
-	ttree = fill_tree_descriptor(&t, sha1);
+		tptree[i] = fill_tree_descriptor(&tp[i], parents_oid[i]->hash);
+	ttree = fill_tree_descriptor(&t, oid->hash);
 
 	/* Enable recursion indefinitely */
 	opt->pathspec.recursive = DIFF_OPT_TST(opt, RECURSIVE);
@@ -548,11 +548,11 @@ static struct combine_diff_path *ll_diff_tree_paths(
 }
 
 struct combine_diff_path *diff_tree_paths(
-	struct combine_diff_path *p, const unsigned char *sha1,
-	const unsigned char **parents_sha1, int nparent,
+	struct combine_diff_path *p, const struct object_id *oid,
+	const struct object_id **parents_oid, int nparent,
 	struct strbuf *base, struct diff_options *opt)
 {
-	p = ll_diff_tree_paths(p, sha1, parents_sha1, nparent, base, opt);
+	p = ll_diff_tree_paths(p, oid, parents_oid, nparent, base, opt);
 
 	/*
 	 * free pre-allocated last element, if any
@@ -577,7 +577,9 @@ static inline int diff_might_be_rename(void)
 		!DIFF_FILE_VALID(diff_queued_diff.queue[0]->one);
 }
 
-static void try_to_follow_renames(const unsigned char *old, const unsigned char *new, struct strbuf *base, struct diff_options *opt)
+static void try_to_follow_renames(const struct object_id *old_oid,
+				  const struct object_id *new_oid,
+				  struct strbuf *base, struct diff_options *opt)
 {
 	struct diff_options diff_opts;
 	struct diff_queue_struct *q = &diff_queued_diff;
@@ -615,7 +617,7 @@ static void try_to_follow_renames(const unsigned char *old, const unsigned char
 	diff_opts.break_opt = opt->break_opt;
 	diff_opts.rename_score = opt->rename_score;
 	diff_setup_done(&diff_opts);
-	ll_diff_tree_sha1(old, new, base, &diff_opts);
+	ll_diff_tree_oid(old_oid, new_oid, base, &diff_opts);
 	diffcore_std(&diff_opts);
 	clear_pathspec(&diff_opts.pathspec);
 
@@ -674,15 +676,16 @@ static void try_to_follow_renames(const unsigned char *old, const unsigned char
 	q->nr = 1;
 }
 
-static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
-			     struct strbuf *base, struct diff_options *opt)
+static int ll_diff_tree_oid(const struct object_id *old_oid,
+			    const struct object_id *new_oid,
+			    struct strbuf *base, struct diff_options *opt)
 {
 	struct combine_diff_path phead, *p;
 	pathchange_fn_t pathchange_old = opt->pathchange;
 
 	phead.next = NULL;
 	opt->pathchange = emit_diff_first_parent_only;
-	diff_tree_paths(&phead, new, &old, 1, base, opt);
+	diff_tree_paths(&phead, new_oid, &old_oid, 1, base, opt);
 
 	for (p = phead.next; p;) {
 		struct combine_diff_path *pprev = p;
@@ -694,7 +697,9 @@ static int ll_diff_tree_sha1(const unsigned char *old, const unsigned char *new,
 	return 0;
 }
 
-int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base_str, struct diff_options *opt)
+int diff_tree_oid(const struct object_id *old_oid,
+		  const struct object_id *new_oid,
+		  const char *base_str, struct diff_options *opt)
 {
 	struct strbuf base;
 	int retval;
@@ -702,16 +707,16 @@ int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const cha
 	strbuf_init(&base, PATH_MAX);
 	strbuf_addstr(&base, base_str);
 
-	retval = ll_diff_tree_sha1(old, new, &base, opt);
+	retval = ll_diff_tree_oid(old_oid, new_oid, &base, opt);
 	if (!*base_str && DIFF_OPT_TST(opt, FOLLOW_RENAMES) && diff_might_be_rename())
-		try_to_follow_renames(old, new, &base, opt);
+		try_to_follow_renames(old_oid, new_oid, &base, opt);
 
 	strbuf_release(&base);
 
 	return retval;
 }
 
-int diff_root_tree_sha1(const unsigned char *new, const char *base, struct diff_options *opt)
+int diff_root_tree_oid(const struct object_id *new_oid, const char *base, struct diff_options *opt)
 {
-	return diff_tree_sha1(NULL, new, base, opt);
+	return diff_tree_oid(NULL, new_oid, base, opt);
 }