Merge branch 'bc/object-id'

Conversion from uchar[20] to struct object_id continues.

* bc/object-id: (36 commits)
  convert: convert to struct object_id
  sha1_file: introduce a constant for max header length
  Convert lookup_replace_object to struct object_id
  sha1_file: convert read_sha1_file to struct object_id
  sha1_file: convert read_object_with_reference to object_id
  tree-walk: convert tree entry functions to object_id
  streaming: convert istream internals to struct object_id
  tree-walk: convert get_tree_entry_follow_symlinks internals to object_id
  builtin/notes: convert static functions to object_id
  builtin/fmt-merge-msg: convert remaining code to object_id
  sha1_file: convert sha1_object_info* to object_id
  Convert remaining callers of sha1_object_info_extended to object_id
  packfile: convert unpack_entry to struct object_id
  sha1_file: convert retry_bad_packed_offset to struct object_id
  sha1_file: convert assert_sha1_type to object_id
  builtin/mktree: convert to struct object_id
  streaming: convert open_istream to use struct object_id
  sha1_file: convert check_sha1_signature to struct object_id
  sha1_file: convert read_loose_object to use struct object_id
  builtin/index-pack: convert struct ref_delta_entry to object_id
  ...

41 files changed, 167 insertions, 166 deletions

diff --git a/builtin/am.c b/builtin/am.c
index 1151b5c73a..1bcc3606c5 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1550,7 +1550,7 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
 	discard_cache();
 	read_cache_from(index_path);
 
-	if (write_index_as_tree(orig_tree.hash, &the_index, index_path, 0, NULL))
+	if (write_index_as_tree(&orig_tree, &the_index, index_path, 0, NULL))
 		return error(_("Repository lacks necessary blobs to fall back on 3-way merge."));
 
 	say(state, stdout, _("Using index info to reconstruct a base tree..."));
@@ -1575,7 +1575,7 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
 		return error(_("Did you hand edit your patch?\n"
 				"It does not apply to blobs recorded in its index."));
 
-	if (write_index_as_tree(their_tree.hash, &the_index, index_path, 0, NULL))
+	if (write_index_as_tree(&their_tree, &the_index, index_path, 0, NULL))
 		return error("could not write tree");
 
 	say(state, stdout, _("Falling back to patching base and 3-way merge..."));
@@ -1626,7 +1626,7 @@ static void do_commit(const struct am_state *state)
 	if (run_hook_le(NULL, "pre-applypatch", NULL))
 		exit(1);
 
-	if (write_cache_as_tree(tree.hash, 0, NULL))
+	if (write_cache_as_tree(&tree, 0, NULL))
 		die(_("git write-tree failed to write a tree"));
 
 	if (!get_oid_commit("HEAD", &parent)) {
@@ -2004,7 +2004,7 @@ static int clean_index(const struct object_id *head, const struct object_id *rem
 	if (fast_forward_to(head_tree, head_tree, 1))
 		return -1;
 
-	if (write_cache_as_tree(index.hash, 0, NULL))
+	if (write_cache_as_tree(&index, 0, NULL))
 		return -1;
 
 	index_tree = parse_tree_indirect(&index);
diff --git a/builtin/blame.c b/builtin/blame.c
index 9dcb367b90..f1a2fd6702 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -499,7 +499,7 @@ static int read_ancestry(const char *graft_file)
 
 static int update_auto_abbrev(int auto_abbrev, struct blame_origin *suspect)
 {
-	const char *uniq = find_unique_abbrev(suspect->commit->object.oid.hash,
+	const char *uniq = find_unique_abbrev(&suspect->commit->object.oid,
 					      auto_abbrev);
 	int len = strlen(uniq);
 	if (auto_abbrev < len)
@@ -655,7 +655,7 @@ static int is_a_rev(const char *name)
 
 	if (get_oid(name, &oid))
 		return 0;
-	return OBJ_NONE < sha1_object_info(oid.hash, NULL);
+	return OBJ_NONE < oid_object_info(&oid, NULL);
 }
 
 int cmd_blame(int argc, const char **argv, const char *prefix)
diff --git a/builtin/branch.c b/builtin/branch.c
index 6d0cea9d4b..5bd2a0dd48 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -273,7 +273,7 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 			       bname.buf,
 			       (flags & REF_ISBROKEN) ? "broken"
 			       : (flags & REF_ISSYMREF) ? target
-			       : find_unique_abbrev(oid.hash, DEFAULT_ABBREV));
+			       : find_unique_abbrev(&oid, DEFAULT_ABBREV));
 		}
 		delete_branch_config(bname.buf);
 
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index d90170f070..2c46d257cd 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -32,7 +32,7 @@ static int filter_object(const char *path, unsigned mode,
 {
 	enum object_type type;
 
-	*buf = read_sha1_file(oid->hash, &type, size);
+	*buf = read_object_file(oid, &type, size);
 	if (!*buf)
 		return error(_("cannot read object %s '%s'"),
 			     oid_to_hex(oid), path);
@@ -77,7 +77,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 	switch (opt) {
 	case 't':
 		oi.type_name = &sb;
-		if (sha1_object_info_extended(oid.hash, &oi, flags) < 0)
+		if (oid_object_info_extended(&oid, &oi, flags) < 0)
 			die("git cat-file: could not get object info");
 		if (sb.len) {
 			printf("%s\n", sb.buf);
@@ -88,7 +88,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 
 	case 's':
 		oi.sizep = &size;
-		if (sha1_object_info_extended(oid.hash, &oi, flags) < 0)
+		if (oid_object_info_extended(&oid, &oi, flags) < 0)
 			die("git cat-file: could not get object info");
 		printf("%lu\n", size);
 		return 0;
@@ -116,7 +116,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 		/* else fallthrough */
 
 	case 'p':
-		type = sha1_object_info(oid.hash, NULL);
+		type = oid_object_info(&oid, NULL);
 		if (type < 0)
 			die("Not a valid object name %s", obj_name);
 
@@ -130,7 +130,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 
 		if (type == OBJ_BLOB)
 			return stream_blob_to_fd(1, &oid, NULL, 0);
-		buf = read_sha1_file(oid.hash, &type, &size);
+		buf = read_object_file(&oid, &type, &size);
 		if (!buf)
 			die("Cannot read object %s", obj_name);
 
@@ -140,8 +140,9 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 	case 0:
 		if (type_from_string(exp_type) == OBJ_BLOB) {
 			struct object_id blob_oid;
-			if (sha1_object_info(oid.hash, NULL) == OBJ_TAG) {
-				char *buffer = read_sha1_file(oid.hash, &type, &size);
+			if (oid_object_info(&oid, NULL) == OBJ_TAG) {
+				char *buffer = read_object_file(&oid, &type,
+								&size);
 				const char *target;
 				if (!skip_prefix(buffer, "object ", &target) ||
 				    get_oid_hex(target, &blob_oid))
@@ -150,7 +151,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 			} else
 				oidcpy(&blob_oid, &oid);
 
-			if (sha1_object_info(blob_oid.hash, NULL) == OBJ_BLOB)
+			if (oid_object_info(&blob_oid, NULL) == OBJ_BLOB)
 				return stream_blob_to_fd(1, &blob_oid, NULL, 0);
 			/*
 			 * we attempted to dereference a tag to a blob
@@ -159,7 +160,7 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 			 * fall-back to the usual case.
 			 */
 		}
-		buf = read_object_with_reference(oid.hash, exp_type, &size, NULL);
+		buf = read_object_with_reference(&oid, exp_type, &size, NULL);
 		break;
 
 	default:
@@ -304,8 +305,9 @@ static void print_object_or_die(struct batch_options *opt, struct expand_data *d
 				enum object_type type;
 				if (!textconv_object(data->rest, 0100644, oid,
 						     1, &contents, &size))
-					contents = read_sha1_file(oid->hash, &type,
-								  &size);
+					contents = read_object_file(oid,
+								    &type,
+								    &size);
 				if (!contents)
 					die("could not convert '%s' %s",
 					    oid_to_hex(oid), data->rest);
@@ -321,7 +323,7 @@ static void print_object_or_die(struct batch_options *opt, struct expand_data *d
 		unsigned long size;
 		void *contents;
 
-		contents = read_sha1_file(oid->hash, &type, &size);
+		contents = read_object_file(oid, &type, &size);
 		if (!contents)
 			die("object %s disappeared", oid_to_hex(oid));
 		if (type != data->type)
@@ -340,8 +342,8 @@ static void batch_object_write(const char *obj_name, struct batch_options *opt,
 	struct strbuf buf = STRBUF_INIT;
 
 	if (!data->skip_object_info &&
-	    sha1_object_info_extended(data->oid.hash, &data->info,
-				      OBJECT_INFO_LOOKUP_REPLACE) < 0) {
+	    oid_object_info_extended(&data->oid, &data->info,
+				     OBJECT_INFO_LOOKUP_REPLACE) < 0) {
 		printf("%s missing\n",
 		       obj_name ? obj_name : oid_to_hex(&data->oid));
 		fflush(stdout);
diff --git a/builtin/checkout.c b/builtin/checkout.c
index d76e13c852..b49b582071 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -66,7 +66,7 @@ static int post_checkout_hook(struct commit *old_commit, struct commit *new_comm
 
 }
 
-static int update_some(const unsigned char *sha1, struct strbuf *base,
+static int update_some(const struct object_id *oid, struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *context)
 {
 	int len;
@@ -78,7 +78,7 @@ static int update_some(const unsigned char *sha1, struct strbuf *base,
 
 	len = base->len + strlen(pathname);
 	ce = xcalloc(1, cache_entry_size(len));
-	hashcpy(ce->oid.hash, sha1);
+	oidcpy(&ce->oid, oid);
 	memcpy(ce->name, base->buf, base->len);
 	memcpy(ce->name + base->len, pathname, len - base->len);
 	ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
@@ -405,10 +405,10 @@ static void describe_detached_head(const char *msg, struct commit *commit)
 		pp_commit_easy(CMIT_FMT_ONELINE, commit, &sb);
 	if (print_sha1_ellipsis()) {
 		fprintf(stderr, "%s %s... %s\n", msg,
-			find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV), sb.buf);
+			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
 	} else {
 		fprintf(stderr, "%s %s %s\n", msg,
-			find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV), sb.buf);
+			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
 	}
 	strbuf_release(&sb);
 }
@@ -720,7 +720,7 @@ static int add_pending_uninteresting_ref(const char *refname,
 static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
 {
 	strbuf_addstr(sb, "  ");
-	strbuf_add_unique_abbrev(sb, commit->object.oid.hash, DEFAULT_ABBREV);
+	strbuf_add_unique_abbrev(sb, &commit->object.oid, DEFAULT_ABBREV);
 	strbuf_addch(sb, ' ');
 	if (!parse_commit(commit))
 		pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
@@ -778,7 +778,7 @@ static void suggest_reattach(struct commit *commit, struct rev_info *revs)
 			" git branch <new-branch-name> %s\n\n",
 			/* Give ngettext() the count */
 			lost),
-			find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV));
+			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
 }
 
 /*
diff --git a/builtin/commit-tree.c b/builtin/commit-tree.c
index e5bdf57b1e..ecf42191da 100644
--- a/builtin/commit-tree.c
+++ b/builtin/commit-tree.c
@@ -58,7 +58,7 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 				usage(commit_tree_usage);
 			if (get_oid_commit(argv[i], &oid))
 				die("Not a valid object name %s", argv[i]);
-			assert_sha1_type(oid.hash, OBJ_COMMIT);
+			assert_oid_type(&oid, OBJ_COMMIT);
 			new_parent(lookup_commit(&oid), &parents);
 			continue;
 		}
diff --git a/builtin/describe.c b/builtin/describe.c
index e4869df7b4..de840f96a4 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -285,7 +285,7 @@ static void append_name(struct commit_name *n, struct strbuf *dst)
 
 static void append_suffix(int depth, const struct object_id *oid, struct strbuf *dst)
 {
-	strbuf_addf(dst, "-%d-g%s", depth, find_unique_abbrev(oid->hash, abbrev));
+	strbuf_addf(dst, "-%d-g%s", depth, find_unique_abbrev(oid, abbrev));
 }
 
 static void describe_commit(struct object_id *oid, struct strbuf *dst)
@@ -383,7 +383,7 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
 	if (!match_cnt) {
 		struct object_id *cmit_oid = &cmit->object.oid;
 		if (always) {
-			strbuf_add_unique_abbrev(dst, cmit_oid->hash, abbrev);
+			strbuf_add_unique_abbrev(dst, cmit_oid, abbrev);
 			if (suffix)
 				strbuf_addstr(dst, suffix);
 			return;
@@ -502,7 +502,7 @@ static void describe(const char *arg, int last_one)
 
 	if (cmit)
 		describe_commit(&oid, &sb);
-	else if (sha1_object_info(oid.hash, NULL) == OBJ_BLOB)
+	else if (oid_object_info(&oid, NULL) == OBJ_BLOB)
 		describe_blob(oid, &sb);
 	else
 		die(_("%s is neither a commit nor blob"), arg);
diff --git a/builtin/difftool.c b/builtin/difftool.c
index bcc79d1888..ee8dce019e 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -306,7 +306,7 @@ static char *get_symlink(const struct object_id *oid, const char *path)
 	} else {
 		enum object_type type;
 		unsigned long size;
-		data = read_sha1_file(oid->hash, &type, &size);
+		data = read_object_file(oid, &type, &size);
 		if (!data)
 			die(_("could not read object %s for symlink %s"),
 				oid_to_hex(oid), path);
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 27b2cc138e..a15898d641 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -237,10 +237,10 @@ static void export_blob(const struct object_id *oid)
 		object = (struct object *)lookup_blob(oid);
 		eaten = 0;
 	} else {
-		buf = read_sha1_file(oid->hash, &type, &size);
+		buf = read_object_file(oid, &type, &size);
 		if (!buf)
 			die ("Could not read blob %s", oid_to_hex(oid));
-		if (check_sha1_signature(oid->hash, buf, size, type_name(type)) < 0)
+		if (check_object_signature(oid, buf, size, type_name(type)) < 0)
 			die("sha1 mismatch in blob %s", oid_to_hex(oid));
 		object = parse_object_buffer(oid, type, size, buf, &eaten);
 	}
@@ -682,7 +682,7 @@ static void handle_tag(const char *name, struct tag *tag)
 		return;
 	}
 
-	buf = read_sha1_file(tag->object.oid.hash, &type, &size);
+	buf = read_object_file(&tag->object.oid, &type, &size);
 	if (!buf)
 		die ("Could not read tag %s", oid_to_hex(&tag->object.oid));
 	message = memmem(buf, size, "\n\n", 2);
@@ -947,7 +947,7 @@ static void import_marks(char *input_file)
 		if (last_idnum < mark)
 			last_idnum = mark;
 
-		type = sha1_object_info(oid.hash, NULL);
+		type = oid_object_info(&oid, NULL);
 		if (type < 0)
 			die("object not found: %s", oid_to_hex(&oid));
 
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 6d73656a48..8295f92b3e 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -637,7 +637,7 @@ static int update_local_ref(struct ref *ref,
 	struct branch *current_branch = branch_get(NULL);
 	const char *pretty_ref = prettify_refname(ref->name);
 
-	type = sha1_object_info(ref->new_oid.hash, NULL);
+	type = oid_object_info(&ref->new_oid, NULL);
 	if (type < 0)
 		die(_("object %s not found"), oid_to_hex(&ref->new_oid));
 
@@ -708,9 +708,9 @@ static int update_local_ref(struct ref *ref,
 	if (in_merge_bases(current, updated)) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
-		strbuf_add_unique_abbrev(&quickref, current->object.oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "..");
-		strbuf_add_unique_abbrev(&quickref, ref->new_oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
 		if ((recurse_submodules != RECURSE_SUBMODULES_OFF) &&
 		    (recurse_submodules != RECURSE_SUBMODULES_ON))
 			check_for_new_submodule_commits(&ref->new_oid);
@@ -723,9 +723,9 @@ static int update_local_ref(struct ref *ref,
 	} else if (force || ref->force) {
 		struct strbuf quickref = STRBUF_INIT;
 		int r;
-		strbuf_add_unique_abbrev(&quickref, current->object.oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &current->object.oid, DEFAULT_ABBREV);
 		strbuf_addstr(&quickref, "...");
-		strbuf_add_unique_abbrev(&quickref, ref->new_oid.hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(&quickref, &ref->new_oid, DEFAULT_ABBREV);
 		if ((recurse_submodules != RECURSE_SUBMODULES_OFF) &&
 		    (recurse_submodules != RECURSE_SUBMODULES_ON))
 			check_for_new_submodule_commits(&ref->new_oid);
diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index 8e8a15ea4a..bd680be687 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -485,10 +485,10 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 	struct strbuf tagbuf = STRBUF_INIT;
 
 	for (i = 0; i < origins.nr; i++) {
-		unsigned char *sha1 = origins.items[i].util;
+		struct object_id *oid = origins.items[i].util;
 		enum object_type type;
 		unsigned long size, len;
-		char *buf = read_sha1_file(sha1, &type, &size);
+		char *buf = read_object_file(oid, &type, &size);
 		struct strbuf sig = STRBUF_INIT;
 
 		if (!buf || type != OBJ_TAG)
diff --git a/builtin/fsck.c b/builtin/fsck.c
index ef78c6c00c..0922558683 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -65,7 +65,7 @@ static const char *printable_type(struct object *obj)
 	const char *ret;
 
 	if (obj->type == OBJ_NONE) {
-		enum object_type type = sha1_object_info(obj->oid.hash, NULL);
+		enum object_type type = oid_object_info(&obj->oid, NULL);
 		if (type > 0)
 			object_as_type(obj, type, 0);
 	}
@@ -513,7 +513,7 @@ static struct object *parse_loose_object(const struct object_id *oid,
 	unsigned long size;
 	int eaten;
 
-	if (read_loose_object(path, oid->hash, &type, &size, &contents) < 0)
+	if (read_loose_object(path, oid, &type, &size, &contents) < 0)
 		return NULL;
 
 	if (!contents && type != OBJ_BLOB)
diff --git a/builtin/grep.c b/builtin/grep.c
index 789a89133a..668cb8050a 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -306,7 +306,7 @@ static void *lock_and_read_oid_file(const struct object_id *oid, enum object_typ
 	void *data;
 
 	grep_read_lock();
-	data = read_sha1_file(oid->hash, type, size);
+	data = read_object_file(oid, type, size);
 	grep_read_unlock();
 	return data;
 }
@@ -452,7 +452,7 @@ static int grep_submodule(struct grep_opt *opt, struct repository *superproject,
 		object = parse_object_or_die(oid, oid_to_hex(oid));
 
 		grep_read_lock();
-		data = read_object_with_reference(object->oid.hash, tree_type,
+		data = read_object_with_reference(&object->oid, tree_type,
 						  &size, NULL);
 		grep_read_unlock();
 
@@ -614,7 +614,7 @@ static int grep_object(struct grep_opt *opt, const struct pathspec *pathspec,
 		int hit, len;
 
 		grep_read_lock();
-		data = read_object_with_reference(obj->oid.hash, tree_type,
+		data = read_object_with_reference(&obj->oid, tree_type,
 						  &size, NULL);
 		grep_read_unlock();
 
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index bda84a92ef..657a5dda06 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -59,7 +59,7 @@ struct ofs_delta_entry {
 };
 
 struct ref_delta_entry {
-	unsigned char sha1[20];
+	struct object_id oid;
 	int obj_no;
 };
 
@@ -222,7 +222,7 @@ static unsigned check_object(struct object *obj)
 
 	if (!(obj->flags & FLAG_CHECKED)) {
 		unsigned long size;
-		int type = sha1_object_info(obj->oid.hash, &size);
+		int type = oid_object_info(&obj->oid, &size);
 		if (type <= 0)
 			die(_("did not receive expected object %s"),
 			      oid_to_hex(&obj->oid));
@@ -672,18 +672,18 @@ static void find_ofs_delta_children(off_t offset,
 	*last_index = last;
 }
 
-static int compare_ref_delta_bases(const unsigned char *sha1,
-				   const unsigned char *sha2,
+static int compare_ref_delta_bases(const struct object_id *oid1,
+				   const struct object_id *oid2,
 				   enum object_type type1,
 				   enum object_type type2)
 {
 	int cmp = type1 - type2;
 	if (cmp)
 		return cmp;
-	return hashcmp(sha1, sha2);
+	return oidcmp(oid1, oid2);
 }
 
-static int find_ref_delta(const unsigned char *sha1, enum object_type type)
+static int find_ref_delta(const struct object_id *oid, enum object_type type)
 {
 	int first = 0, last = nr_ref_deltas;
 
@@ -692,7 +692,7 @@ static int find_ref_delta(const unsigned char *sha1, enum object_type type)
 		struct ref_delta_entry *delta = &ref_deltas[next];
 		int cmp;
 
-		cmp = compare_ref_delta_bases(sha1, delta->sha1,
+		cmp = compare_ref_delta_bases(oid, &delta->oid,
 					      type, objects[delta->obj_no].type);
 		if (!cmp)
 			return next;
@@ -705,11 +705,11 @@ static int find_ref_delta(const unsigned char *sha1, enum object_type type)
 	return -first-1;
 }
 
-static void find_ref_delta_children(const unsigned char *sha1,
+static void find_ref_delta_children(const struct object_id *oid,
 				    int *first_index, int *last_index,
 				    enum object_type type)
 {
-	int first = find_ref_delta(sha1, type);
+	int first = find_ref_delta(oid, type);
 	int last = first;
 	int end = nr_ref_deltas - 1;
 
@@ -718,9 +718,9 @@ static void find_ref_delta_children(const unsigned char *sha1,
 		*last_index = -1;
 		return;
 	}
-	while (first > 0 && !hashcmp(ref_deltas[first - 1].sha1, sha1))
+	while (first > 0 && !oidcmp(&ref_deltas[first - 1].oid, oid))
 		--first;
-	while (last < end && !hashcmp(ref_deltas[last + 1].sha1, sha1))
+	while (last < end && !oidcmp(&ref_deltas[last + 1].oid, oid))
 		++last;
 	*first_index = first;
 	*last_index = last;
@@ -772,7 +772,7 @@ static int check_collison(struct object_entry *entry)
 
 	memset(&data, 0, sizeof(data));
 	data.entry = entry;
-	data.st = open_istream(entry->idx.oid.hash, &type, &size, NULL);
+	data.st = open_istream(&entry->idx.oid, &type, &size, NULL);
 	if (!data.st)
 		return -1;
 	if (size != entry->size || type != entry->type)
@@ -811,12 +811,12 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
 		enum object_type has_type;
 		unsigned long has_size;
 		read_lock();
-		has_type = sha1_object_info(oid->hash, &has_size);
+		has_type = oid_object_info(oid, &has_size);
 		if (has_type < 0)
 			die(_("cannot read existing object info %s"), oid_to_hex(oid));
 		if (has_type != type || has_size != size)
 			die(_("SHA1 COLLISION FOUND WITH %s !"), oid_to_hex(oid));
-		has_data = read_sha1_file(oid->hash, &has_type, &has_size);
+		has_data = read_object_file(oid, &has_type, &has_size);
 		read_unlock();
 		if (!data)
 			data = new_data = get_data_from_pack(obj_entry);
@@ -992,7 +992,7 @@ static struct base_data *find_unresolved_deltas_1(struct base_data *base,
 						  struct base_data *prev_base)
 {
 	if (base->ref_last == -1 && base->ofs_last == -1) {
-		find_ref_delta_children(base->obj->idx.oid.hash,
+		find_ref_delta_children(&base->obj->idx.oid,
 					&base->ref_first, &base->ref_last,
 					OBJ_REF_DELTA);
 
@@ -1076,7 +1076,7 @@ static int compare_ref_delta_entry(const void *a, const void *b)
 	const struct ref_delta_entry *delta_a = a;
 	const struct ref_delta_entry *delta_b = b;
 
-	return hashcmp(delta_a->sha1, delta_b->sha1);
+	return oidcmp(&delta_a->oid, &delta_b->oid);
 }
 
 static void resolve_base(struct object_entry *obj)
@@ -1142,7 +1142,7 @@ static void parse_pack_objects(unsigned char *hash)
 			ofs_delta++;
 		} else if (obj->type == OBJ_REF_DELTA) {
 			ALLOC_GROW(ref_deltas, nr_ref_deltas + 1, ref_deltas_alloc);
-			hashcpy(ref_deltas[nr_ref_deltas].sha1, ref_delta_oid.hash);
+			oidcpy(&ref_deltas[nr_ref_deltas].oid, &ref_delta_oid);
 			ref_deltas[nr_ref_deltas].obj_no = i;
 			nr_ref_deltas++;
 		} else if (!data) {
@@ -1374,14 +1374,15 @@ static void fix_unresolved_deltas(struct hashfile *f)
 
 		if (objects[d->obj_no].real_type != OBJ_REF_DELTA)
 			continue;
-		base_obj->data = read_sha1_file(d->sha1, &type, &base_obj->size);
+		base_obj->data = read_object_file(&d->oid, &type,
+						  &base_obj->size);
 		if (!base_obj->data)
 			continue;
 
-		if (check_sha1_signature(d->sha1, base_obj->data,
+		if (check_object_signature(&d->oid, base_obj->data,
 				base_obj->size, type_name(type)))
-			die(_("local object %s is corrupt"), sha1_to_hex(d->sha1));
-		base_obj->obj = append_obj_to_pack(f, d->sha1,
+			die(_("local object %s is corrupt"), oid_to_hex(&d->oid));
+		base_obj->obj = append_obj_to_pack(f, d->oid.hash,
 					base_obj->data, base_obj->size, type);
 		find_unresolved_deltas(base_obj);
 		display_progress(progress, nr_resolved_deltas);
diff --git a/builtin/log.c b/builtin/log.c
index 94ee177d56..71f68a3e4f 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -518,7 +518,7 @@ static int show_tag_object(const struct object_id *oid, struct rev_info *rev)
 {
 	unsigned long size;
 	enum object_type type;
-	char *buf = read_sha1_file(oid->hash, &type, &size);
+	char *buf = read_object_file(oid, &type, &size);
 	int offset = 0;
 
 	if (!buf)
@@ -541,7 +541,7 @@ static int show_tag_object(const struct object_id *oid, struct rev_info *rev)
 	return 0;
 }
 
-static int show_tree_object(const unsigned char *sha1,
+static int show_tree_object(const struct object_id *oid,
 		struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *context)
 {
@@ -1873,12 +1873,12 @@ static void print_commit(char sign, struct commit *commit, int verbose,
 {
 	if (!verbose) {
 		fprintf(file, "%c %s\n", sign,
-		       find_unique_abbrev(commit->object.oid.hash, abbrev));
+		       find_unique_abbrev(&commit->object.oid, abbrev));
 	} else {
 		struct strbuf buf = STRBUF_INIT;
 		pp_commit_easy(CMIT_FMT_ONELINE, commit, &buf);
 		fprintf(file, "%c %s %s\n", sign,
-		       find_unique_abbrev(commit->object.oid.hash, abbrev),
+		       find_unique_abbrev(&commit->object.oid, abbrev),
 		       buf.buf);
 		strbuf_release(&buf);
 	}
diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index 2fc836e330..a71f6bd088 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -240,7 +240,7 @@ static void show_ce(struct repository *repo, struct dir_struct *dir,
 			printf("%s%06o %s %d\t",
 			       tag,
 			       ce->ce_mode,
-			       find_unique_abbrev(ce->oid.hash, abbrev),
+			       find_unique_abbrev(&ce->oid, abbrev),
 			       ce_stage(ce));
 		}
 		write_eolinfo(repo->index, ce, fullname);
@@ -271,7 +271,7 @@ static void show_ru_info(const struct index_state *istate)
 			if (!ui->mode[i])
 				continue;
 			printf("%s%06o %s %d\t", tag_resolve_undo, ui->mode[i],
-			       find_unique_abbrev(ui->sha1[i], abbrev),
+			       find_unique_abbrev(&ui->oid[i], abbrev),
 			       i + 1);
 			write_name(path);
 		}
diff --git a/builtin/ls-tree.c b/builtin/ls-tree.c
index ef965408e8..d44b4f9c27 100644
--- a/builtin/ls-tree.c
+++ b/builtin/ls-tree.c
@@ -60,7 +60,7 @@ static int show_recursive(const char *base, int baselen, const char *pathname)
 	return 0;
 }
 
-static int show_tree(const unsigned char *sha1, struct strbuf *base,
+static int show_tree(const struct object_id *oid, struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *context)
 {
 	int retval = 0;
@@ -94,7 +94,7 @@ static int show_tree(const unsigned char *sha1, struct strbuf *base,
 			char size_text[24];
 			if (!strcmp(type, blob_type)) {
 				unsigned long size;
-				if (sha1_object_info(sha1, &size) == OBJ_BAD)
+				if (oid_object_info(oid, &size) == OBJ_BAD)
 					xsnprintf(size_text, sizeof(size_text),
 						  "BAD");
 				else
@@ -103,11 +103,11 @@ static int show_tree(const unsigned char *sha1, struct strbuf *base,
 			} else
 				xsnprintf(size_text, sizeof(size_text), "-");
 			printf("%06o %s %s %7s\t", mode, type,
-			       find_unique_abbrev(sha1, abbrev),
+			       find_unique_abbrev(oid, abbrev),
 			       size_text);
 		} else
 			printf("%06o %s %s\t", mode, type,
-			       find_unique_abbrev(sha1, abbrev));
+			       find_unique_abbrev(oid, abbrev));
 	}
 	baselen = base->len;
 	strbuf_addstr(base, pathname);
diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index d01ddecf66..32736e0b10 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -60,7 +60,7 @@ static void *result(struct merge_list *entry, unsigned long *size)
 	const char *path = entry->path;
 
 	if (!entry->stage)
-		return read_sha1_file(entry->blob->object.oid.hash, &type, size);
+		return read_object_file(&entry->blob->object.oid, &type, size);
 	base = NULL;
 	if (entry->stage == 1) {
 		base = entry->blob;
@@ -82,7 +82,8 @@ static void *origin(struct merge_list *entry, unsigned long *size)
 	enum object_type type;
 	while (entry) {
 		if (entry->stage == 2)
-			return read_sha1_file(entry->blob->object.oid.hash, &type, size);
+			return read_object_file(&entry->blob->object.oid,
+						&type, size);
 		entry = entry->link;
 	}
 	return NULL;
diff --git a/builtin/merge.c b/builtin/merge.c
index ee050a47f3..8746c5e3e8 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -639,7 +639,7 @@ static int read_tree_trivial(struct object_id *common, struct object_id *head,
 
 static void write_tree_trivial(struct object_id *oid)
 {
-	if (write_cache_as_tree(oid->hash, 0, NULL))
+	if (write_cache_as_tree(oid, 0, NULL))
 		die(_("git write-tree failed to write a tree"));
 }
 
@@ -1324,7 +1324,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 			check_commit_signature(commit, &signature_check);
 
-			find_unique_abbrev_r(hex, commit->object.oid.hash, DEFAULT_ABBREV);
+			find_unique_abbrev_r(hex, &commit->object.oid, DEFAULT_ABBREV);
 			switch (signature_check.result) {
 			case 'G':
 				break;
@@ -1417,9 +1417,9 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 
 		if (verbosity >= 0) {
 			printf(_("Updating %s..%s\n"),
-			       find_unique_abbrev(head_commit->object.oid.hash,
+			       find_unique_abbrev(&head_commit->object.oid,
 						  DEFAULT_ABBREV),
-			       find_unique_abbrev(remoteheads->item->object.oid.hash,
+			       find_unique_abbrev(&remoteheads->item->object.oid,
 						  DEFAULT_ABBREV));
 		}
 		strbuf_addstr(&msg, "Fast-forward");
diff --git a/builtin/mktag.c b/builtin/mktag.c
index beb552847b..9f5a50a8fd 100644
--- a/builtin/mktag.c
+++ b/builtin/mktag.c
@@ -18,17 +18,17 @@
 /*
  * We refuse to tag something we can't verify. Just because.
  */
-static int verify_object(const unsigned char *sha1, const char *expected_type)
+static int verify_object(const struct object_id *oid, const char *expected_type)
 {
 	int ret = -1;
 	enum object_type type;
 	unsigned long size;
-	void *buffer = read_sha1_file(sha1, &type, &size);
-	const unsigned char *repl = lookup_replace_object(sha1);
+	void *buffer = read_object_file(oid, &type, &size);
+	const struct object_id *repl = lookup_replace_object(oid);
 
 	if (buffer) {
 		if (type == type_from_string(expected_type))
-			ret = check_sha1_signature(repl, buffer, size, expected_type);
+			ret = check_object_signature(repl, buffer, size, expected_type);
 		free(buffer);
 	}
 	return ret;
@@ -38,8 +38,8 @@ static int verify_tag(char *buffer, unsigned long size)
 {
 	int typelen;
 	char type[20];
-	unsigned char sha1[20];
-	const char *object, *type_line, *tag_line, *tagger_line, *lb, *rb;
+	struct object_id oid;
+	const char *object, *type_line, *tag_line, *tagger_line, *lb, *rb, *p;
 	size_t len;
 
 	if (size < 84)
@@ -52,11 +52,11 @@ static int verify_tag(char *buffer, unsigned long size)
 	if (memcmp(object, "object ", 7))
 		return error("char%d: does not start with \"object \"", 0);
 
-	if (get_sha1_hex(object + 7, sha1))
+	if (parse_oid_hex(object + 7, &oid, &p))
 		return error("char%d: could not get SHA1 hash", 7);
 
 	/* Verify type line */
-	type_line = object + 48;
+	type_line = p + 1;
 	if (memcmp(type_line - 1, "\ntype ", 6))
 		return error("char%d: could not find \"\\ntype \"", 47);
 
@@ -80,8 +80,8 @@ static int verify_tag(char *buffer, unsigned long size)
 	type[typelen] = 0;
 
 	/* Verify that the object matches */
-	if (verify_object(sha1, type))
-		return error("char%d: could not verify object %s", 7, sha1_to_hex(sha1));
+	if (verify_object(&oid, type))
+		return error("char%d: could not verify object %s", 7, oid_to_hex(&oid));
 
 	/* Verify the tag-name: we don't allow control characters or spaces in it */
 	tag_line += 4;
diff --git a/builtin/mktree.c b/builtin/mktree.c
index f5f3c0eea1..263c530315 100644
--- a/builtin/mktree.c
+++ b/builtin/mktree.c
@@ -10,13 +10,13 @@
 
 static struct treeent {
 	unsigned mode;
-	unsigned char sha1[20];
+	struct object_id oid;
 	int len;
 	char name[FLEX_ARRAY];
 } **entries;
 static int alloc, used;
 
-static void append_to_tree(unsigned mode, unsigned char *sha1, char *path)
+static void append_to_tree(unsigned mode, struct object_id *oid, char *path)
 {
 	struct treeent *ent;
 	size_t len = strlen(path);
@@ -26,7 +26,7 @@ static void append_to_tree(unsigned mode, unsigned char *sha1, char *path)
 	FLEX_ALLOC_MEM(ent, name, path, len);
 	ent->mode = mode;
 	ent->len = len;
-	hashcpy(ent->sha1, sha1);
+	oidcpy(&ent->oid, oid);
 
 	ALLOC_GROW(entries, used + 1, alloc);
 	entries[used++] = ent;
@@ -54,7 +54,7 @@ static void write_tree(struct object_id *oid)
 	for (i = 0; i < used; i++) {
 		struct treeent *ent = entries[i];
 		strbuf_addf(&buf, "%o %s%c", ent->mode, ent->name, '\0');
-		strbuf_add(&buf, ent->sha1, 20);
+		strbuf_add(&buf, ent->oid.hash, the_hash_algo->rawsz);
 	}
 
 	write_object_file(buf.buf, buf.len, tree_type, oid);
@@ -69,11 +69,12 @@ static const char *mktree_usage[] = {
 static void mktree_line(char *buf, size_t len, int nul_term_line, int allow_missing)
 {
 	char *ptr, *ntr;
+	const char *p;
 	unsigned mode;
 	enum object_type mode_type; /* object type derived from mode */
 	enum object_type obj_type; /* object type derived from sha */
 	char *path, *to_free = NULL;
-	unsigned char sha1[20];
+	struct object_id oid;
 
 	ptr = buf;
 	/*
@@ -85,9 +86,8 @@ static void mktree_line(char *buf, size_t len, int nul_term_line, int allow_miss
 		die("input format error: %s", buf);
 	ptr = ntr + 1; /* type */
 	ntr = strchr(ptr, ' ');
-	if (!ntr || buf + len <= ntr + 40 ||
-	    ntr[41] != '\t' ||
-	    get_sha1_hex(ntr + 1, sha1))
+	if (!ntr || parse_oid_hex(ntr + 1, &oid, &p) ||
+	    *p != '\t')
 		die("input format error: %s", buf);
 
 	/* It is perfectly normal if we do not have a commit from a submodule */
@@ -116,12 +116,12 @@ static void mktree_line(char *buf, size_t len, int nul_term_line, int allow_miss
 	}
 
 	/* Check the type of object identified by sha1 */
-	obj_type = sha1_object_info(sha1, NULL);
+	obj_type = oid_object_info(&oid, NULL);
 	if (obj_type < 0) {
 		if (allow_missing) {
 			; /* no problem - missing objects are presumed to be of the right type */
 		} else {
-			die("entry '%s' object %s is unavailable", path, sha1_to_hex(sha1));
+			die("entry '%s' object %s is unavailable", path, oid_to_hex(&oid));
 		}
 	} else {
 		if (obj_type != mode_type) {
@@ -131,11 +131,11 @@ static void mktree_line(char *buf, size_t len, int nul_term_line, int allow_miss
 			 * because the new tree entry will never be correct.
 			 */
 			die("entry '%s' object %s is a %s but specified type was (%s)",
-				path, sha1_to_hex(sha1), type_name(obj_type), type_name(mode_type));
+				path, oid_to_hex(&oid), type_name(obj_type), type_name(mode_type));
 		}
 	}
 
-	append_to_tree(mode, sha1, path);
+	append_to_tree(mode, &oid, path);
 	free(to_free);
 }
 
diff --git a/builtin/name-rev.c b/builtin/name-rev.c
index 9e088ebd11..387ddf85d2 100644
--- a/builtin/name-rev.c
+++ b/builtin/name-rev.c
@@ -328,7 +328,7 @@ static void show_name(const struct object *obj,
 	else if (allow_undefined)
 		printf("undefined\n");
 	else if (always)
-		printf("%s\n", find_unique_abbrev(oid->hash, DEFAULT_ABBREV));
+		printf("%s\n", find_unique_abbrev(oid, DEFAULT_ABBREV));
 	else
 		die("cannot describe '%s'", oid_to_hex(oid));
 	strbuf_release(&buf);
diff --git a/builtin/notes.c b/builtin/notes.c
index 6d2fda4a7d..921e08d5bf 100644
--- a/builtin/notes.c
+++ b/builtin/notes.c
@@ -118,11 +118,11 @@ static int list_each_note(const struct object_id *object_oid,
 	return 0;
 }
 
-static void copy_obj_to_fd(int fd, const unsigned char *sha1)
+static void copy_obj_to_fd(int fd, const struct object_id *oid)
 {
 	unsigned long size;
 	enum object_type type;
-	char *buf = read_sha1_file(sha1, &type, &size);
+	char *buf = read_object_file(oid, &type, &size);
 	if (buf) {
 		if (size)
 			write_or_die(fd, buf, size);
@@ -162,7 +162,7 @@ static void write_commented_object(int fd, const struct object_id *object)
 }
 
 static void prepare_note_data(const struct object_id *object, struct note_data *d,
-		const unsigned char *old_note)
+		const struct object_id *old_note)
 {
 	if (d->use_editor || !d->given) {
 		int fd;
@@ -253,7 +253,7 @@ static int parse_reuse_arg(const struct option *opt, const char *arg, int unset)
 
 	if (get_oid(arg, &object))
 		die(_("failed to resolve '%s' as a valid ref."), arg);
-	if (!(buf = read_sha1_file(object.hash, &type, &len))) {
+	if (!(buf = read_object_file(&object, &type, &len))) {
 		free(buf);
 		die(_("failed to read object '%s'."), arg);
 	}
@@ -457,7 +457,7 @@ static int add(int argc, const char **argv, const char *prefix)
 			oid_to_hex(&object));
 	}
 
-	prepare_note_data(&object, &d, note ? note->hash : NULL);
+	prepare_note_data(&object, &d, note);
 	if (d.buf.len || allow_empty) {
 		write_note_data(&d, &new_note);
 		if (add_note(t, &object, &new_note, combine_notes_overwrite))
@@ -602,13 +602,13 @@ static int append_edit(int argc, const char **argv, const char *prefix)
 	t = init_notes_check(argv[0], NOTES_INIT_WRITABLE);
 	note = get_note(t, &object);
 
-	prepare_note_data(&object, &d, edit && note ? note->hash : NULL);
+	prepare_note_data(&object, &d, edit && note ? note : NULL);
 
 	if (note && !edit) {
 		/* Append buf to previous note contents */
 		unsigned long size;
 		enum object_type type;
-		char *prev_buf = read_sha1_file(note->hash, &type, &size);
+		char *prev_buf = read_object_file(note, &type, &size);
 
 		strbuf_grow(&d.buf, size + 1);
 		if (d.buf.len && prev_buf && size)
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index e9d3cfb9e3..e7e673266e 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -122,11 +122,10 @@ static void *get_delta(struct object_entry *entry)
 	void *buf, *base_buf, *delta_buf;
 	enum object_type type;
 
-	buf = read_sha1_file(entry->idx.oid.hash, &type, &size);
+	buf = read_object_file(&entry->idx.oid, &type, &size);
 	if (!buf)
 		die("unable to read %s", oid_to_hex(&entry->idx.oid));
-	base_buf = read_sha1_file(entry->delta->idx.oid.hash, &type,
-				  &base_size);
+	base_buf = read_object_file(&entry->delta->idx.oid, &type, &base_size);
 	if (!base_buf)
 		die("unable to read %s",
 		    oid_to_hex(&entry->delta->idx.oid));
@@ -267,11 +266,10 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 	if (!usable_delta) {
 		if (entry->type == OBJ_BLOB &&
 		    entry->size > big_file_threshold &&
-		    (st = open_istream(entry->idx.oid.hash, &type, &size, NULL)) != NULL)
+		    (st = open_istream(&entry->idx.oid, &type, &size, NULL)) != NULL)
 			buf = NULL;
 		else {
-			buf = read_sha1_file(entry->idx.oid.hash, &type,
-					     &size);
+			buf = read_object_file(&entry->idx.oid, &type, &size);
 			if (!buf)
 				die(_("unable to read %s"),
 				    oid_to_hex(&entry->idx.oid));
@@ -1190,7 +1188,7 @@ static struct pbase_tree_cache *pbase_tree_get(const struct object_id *oid)
 	/* Did not find one.  Either we got a bogus request or
 	 * we need to read and perhaps cache.
 	 */
-	data = read_sha1_file(oid->hash, &type, &size);
+	data = read_object_file(oid, &type, &size);
 	if (!data)
 		return NULL;
 	if (type != OBJ_TREE) {
@@ -1351,7 +1349,7 @@ static void add_preferred_base(struct object_id *oid)
 	if (window <= num_preferred_base++)
 		return;
 
-	data = read_object_with_reference(oid->hash, tree_type, &size, tree_oid.hash);
+	data = read_object_with_reference(oid, tree_type, &size, &tree_oid);
 	if (!data)
 		return;
 
@@ -1516,7 +1514,7 @@ static void check_object(struct object_entry *entry)
 		unuse_pack(&w_curs);
 	}
 
-	entry->type = sha1_object_info(entry->idx.oid.hash, &entry->size);
+	entry->type = oid_object_info(&entry->idx.oid, &entry->size);
 	/*
 	 * The error condition is checked in prepare_pack().  This is
 	 * to permit a missing preferred base object to be ignored
@@ -1578,8 +1576,7 @@ static void drop_reused_delta(struct object_entry *entry)
 		 * And if that fails, the error will be recorded in entry->type
 		 * and dealt with in prepare_pack().
 		 */
-		entry->type = sha1_object_info(entry->idx.oid.hash,
-					       &entry->size);
+		entry->type = oid_object_info(&entry->idx.oid, &entry->size);
 	}
 }
 
@@ -1871,8 +1868,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	/* Load data if not already done */
 	if (!trg->data) {
 		read_lock();
-		trg->data = read_sha1_file(trg_entry->idx.oid.hash, &type,
-					   &sz);
+		trg->data = read_object_file(&trg_entry->idx.oid, &type, &sz);
 		read_unlock();
 		if (!trg->data)
 			die("object %s cannot be read",
@@ -1885,8 +1881,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	}
 	if (!src->data) {
 		read_lock();
-		src->data = read_sha1_file(src_entry->idx.oid.hash, &type,
-					   &sz);
+		src->data = read_object_file(&src_entry->idx.oid, &type, &sz);
 		read_unlock();
 		if (!src->data) {
 			if (src_entry->preferred_base) {
@@ -2709,7 +2704,7 @@ static void add_objects_in_unpacked_packs(struct rev_info *revs)
 static int add_loose_object(const struct object_id *oid, const char *path,
 			    void *data)
 {
-	enum object_type type = sha1_object_info(oid->hash, NULL);
+	enum object_type type = oid_object_info(oid, NULL);
 
 	if (type < 0) {
 		warning("loose object at %s could not be examined", path);
diff --git a/builtin/prune.c b/builtin/prune.c
index 4394d01c93..38ced18dad 100644
--- a/builtin/prune.c
+++ b/builtin/prune.c
@@ -50,7 +50,7 @@ static int prune_object(const struct object_id *oid, const char *fullpath,
 	if (st.st_mtime > expire)
 		return 0;
 	if (show_only || verbose) {
-		enum object_type type = sha1_object_info(oid->hash, NULL);
+		enum object_type type = oid_object_info(oid, NULL);
 		printf("%s %s\n", oid_to_hex(oid),
 		       (type > 0) ? type_name(type) : "unknown");
 	}
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 75e7f18ace..2bf7f2d1a3 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1242,11 +1242,11 @@ static void check_aliased_update(struct command *cmd, struct string_list *list)
 	rp_error("refusing inconsistent update between symref '%s' (%s..%s) and"
 		 " its target '%s' (%s..%s)",
 		 cmd->ref_name,
-		 find_unique_abbrev(cmd->old_oid.hash, DEFAULT_ABBREV),
-		 find_unique_abbrev(cmd->new_oid.hash, DEFAULT_ABBREV),
+		 find_unique_abbrev(&cmd->old_oid, DEFAULT_ABBREV),
+		 find_unique_abbrev(&cmd->new_oid, DEFAULT_ABBREV),
 		 dst_cmd->ref_name,
-		 find_unique_abbrev(dst_cmd->old_oid.hash, DEFAULT_ABBREV),
-		 find_unique_abbrev(dst_cmd->new_oid.hash, DEFAULT_ABBREV));
+		 find_unique_abbrev(&dst_cmd->old_oid, DEFAULT_ABBREV),
+		 find_unique_abbrev(&dst_cmd->new_oid, DEFAULT_ABBREV));
 
 	cmd->error_string = dst_cmd->error_string =
 		"inconsistent aliased update";
diff --git a/builtin/reflog.c b/builtin/reflog.c
index 4719a5354c..a89bd1dd25 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -75,7 +75,7 @@ static int tree_is_complete(const struct object_id *oid)
 	if (!tree->buffer) {
 		enum object_type type;
 		unsigned long size;
-		void *data = read_sha1_file(oid->hash, &type, &size);
+		void *data = read_object_file(oid, &type, &size);
 		if (!data) {
 			tree->object.flags |= INCOMPLETE;
 			return 0;
diff --git a/builtin/replace.c b/builtin/replace.c
index 482f12018f..935647be6b 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -53,8 +53,8 @@ static int show_reference(const char *refname, const struct object_id *oid,
 			if (get_oid(refname, &object))
 				return error("Failed to resolve '%s' as a valid ref.", refname);
 
-			obj_type = sha1_object_info(object.hash, NULL);
-			repl_type = sha1_object_info(oid->hash, NULL);
+			obj_type = oid_object_info(&object, NULL);
+			repl_type = oid_object_info(oid, NULL);
 
 			printf("%s (%s) -> %s (%s)\n", refname, type_name(obj_type),
 			       oid_to_hex(oid), type_name(repl_type));
@@ -162,8 +162,8 @@ static int replace_object_oid(const char *object_ref,
 	struct ref_transaction *transaction;
 	struct strbuf err = STRBUF_INIT;
 
-	obj_type = sha1_object_info(object->hash, NULL);
-	repl_type = sha1_object_info(repl->hash, NULL);
+	obj_type = oid_object_info(object, NULL);
+	repl_type = oid_object_info(repl, NULL);
 	if (!force && obj_type != repl_type)
 		die("Objects must be of the same type.\n"
 		    "'%s' points to a replaced object of type '%s'\n"
@@ -290,7 +290,7 @@ static int edit_and_replace(const char *object_ref, int force, int raw)
 	if (get_oid(object_ref, &old_oid) < 0)
 		die("Not a valid object name: '%s'", object_ref);
 
-	type = sha1_object_info(old_oid.hash, NULL);
+	type = oid_object_info(&old_oid, NULL);
 	if (type < 0)
 		die("unable to get object type for %s", oid_to_hex(&old_oid));
 
diff --git a/builtin/reset.c b/builtin/reset.c
index 5da0f75de9..7f1c3f02a3 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -109,7 +109,7 @@ static void print_new_head_line(struct commit *commit)
 	struct strbuf buf = STRBUF_INIT;
 
 	printf(_("HEAD is now at %s"),
-		find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV));
+		find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
 
 	pp_commit_easy(CMIT_FMT_ONELINE, commit, &buf);
 	if (buf.len > 0)
diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 6f5b9b0847..fadd3ec14c 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -108,7 +108,7 @@ static void show_commit(struct commit *commit, void *data)
 	if (!revs->graph)
 		fputs(get_revision_mark(revs, commit), stdout);
 	if (revs->abbrev_commit && revs->abbrev)
-		fputs(find_unique_abbrev(commit->object.oid.hash, revs->abbrev),
+		fputs(find_unique_abbrev(&commit->object.oid, revs->abbrev),
 		      stdout);
 	else
 		fputs(oid_to_hex(&commit->object.oid), stdout);
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index a1e680b5e9..36b2087782 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -159,7 +159,7 @@ static void show_rev(int type, const struct object_id *oid, const char *name)
 		}
 	}
 	else if (abbrev)
-		show_with_type(type, find_unique_abbrev(oid->hash, abbrev));
+		show_with_type(type, find_unique_abbrev(oid, abbrev));
 	else
 		show_with_type(type, oid_to_hex(oid));
 }
diff --git a/builtin/rm.c b/builtin/rm.c
index 4447bb4d0f..5b6fc7ee81 100644
--- a/builtin/rm.c
+++ b/builtin/rm.c
@@ -178,7 +178,7 @@ static int check_local_mod(struct object_id *head, int index_only)
 		 * way as changed from the HEAD.
 		 */
 		if (no_head
-		     || get_tree_entry(head->hash, name, oid.hash, &mode)
+		     || get_tree_entry(head, name, &oid, &mode)
 		     || ce->ce_mode != create_ce_mode(mode)
 		     || oidcmp(&ce->oid, &oid))
 			staged_changes = 1;
diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index e8a4aa40cb..6c2148b71d 100644
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -292,7 +292,7 @@ static void show_one_commit(struct commit *commit, int no_name)
 		}
 		else
 			printf("[%s] ",
-			       find_unique_abbrev(commit->object.oid.hash,
+			       find_unique_abbrev(&commit->object.oid,
 						  DEFAULT_ABBREV));
 	}
 	puts(pretty_str);
diff --git a/builtin/show-ref.c b/builtin/show-ref.c
index 41e5e71cad..f2eb1a7724 100644
--- a/builtin/show-ref.c
+++ b/builtin/show-ref.c
@@ -29,7 +29,7 @@ static void show_one(const char *refname, const struct object_id *oid)
 	if (quiet)
 		return;
 
-	hex = find_unique_abbrev(oid->hash, abbrev);
+	hex = find_unique_abbrev(oid, abbrev);
 	if (hash_only)
 		printf("%s\n", hex);
 	else
@@ -39,7 +39,7 @@ static void show_one(const char *refname, const struct object_id *oid)
 		return;
 
 	if (!peel_ref(refname, &peeled)) {
-		hex = find_unique_abbrev(peeled.hash, abbrev);
+		hex = find_unique_abbrev(&peeled, abbrev);
 		printf("%s %s^{}\n", hex, refname);
 	}
 }
diff --git a/builtin/tag.c b/builtin/tag.c
index da186691ed..8cff6d0b72 100644
--- a/builtin/tag.c
+++ b/builtin/tag.c
@@ -99,7 +99,8 @@ static int delete_tag(const char *name, const char *ref,
 {
 	if (delete_ref(NULL, ref, oid, 0))
 		return 1;
-	printf(_("Deleted tag '%s' (was %s)\n"), name, find_unique_abbrev(oid->hash, DEFAULT_ABBREV));
+	printf(_("Deleted tag '%s' (was %s)\n"), name,
+	       find_unique_abbrev(oid, DEFAULT_ABBREV));
 	return 0;
 }
 
@@ -167,7 +168,7 @@ static void write_tag_body(int fd, const struct object_id *oid)
 	enum object_type type;
 	char *buf, *sp;
 
-	buf = read_sha1_file(oid->hash, &type, &size);
+	buf = read_object_file(oid, &type, &size);
 	if (!buf)
 		return;
 	/* skip header */
@@ -211,7 +212,7 @@ static void create_tag(const struct object_id *object, const char *tag,
 	struct strbuf header = STRBUF_INIT;
 	char *path = NULL;
 
-	type = sha1_object_info(object->hash, NULL);
+	type = oid_object_info(object, NULL);
 	if (type <= OBJ_NONE)
 	    die(_("bad object type."));
 
@@ -293,17 +294,17 @@ static void create_reflog_msg(const struct object_id *oid, struct strbuf *sb)
 		strbuf_addstr(sb, rla);
 	} else {
 		strbuf_addstr(sb, "tag: tagging ");
-		strbuf_add_unique_abbrev(sb, oid->hash, DEFAULT_ABBREV);
+		strbuf_add_unique_abbrev(sb, oid, DEFAULT_ABBREV);
 	}
 
 	strbuf_addstr(sb, " (");
-	type = sha1_object_info(oid->hash, NULL);
+	type = oid_object_info(oid, NULL);
 	switch (type) {
 	default:
 		strbuf_addstr(sb, "object of unknown type");
 		break;
 	case OBJ_COMMIT:
-		if ((buf = read_sha1_file(oid->hash, &type, &size)) != NULL) {
+		if ((buf = read_object_file(oid, &type, &size)) != NULL) {
 			subject_len = find_commit_subject(buf, &subject_start);
 			strbuf_insert(sb, sb->len, subject_start, subject_len);
 		} else {
@@ -558,7 +559,8 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 		die("%s", err.buf);
 	ref_transaction_free(transaction);
 	if (force && !is_null_oid(&prev) && oidcmp(&prev, &object))
-		printf(_("Updated tag '%s' (was %s)\n"), tag, find_unique_abbrev(prev.hash, DEFAULT_ABBREV));
+		printf(_("Updated tag '%s' (was %s)\n"), tag,
+		       find_unique_abbrev(&prev, DEFAULT_ABBREV));
 
 	UNLEAK(buf);
 	UNLEAK(ref);
diff --git a/builtin/unpack-file.c b/builtin/unpack-file.c
index 32e0155577..300eb59657 100644
--- a/builtin/unpack-file.c
+++ b/builtin/unpack-file.c
@@ -9,7 +9,7 @@ static char *create_temp_file(struct object_id *oid)
 	unsigned long size;
 	int fd;
 
-	buf = read_sha1_file(oid->hash, &type, &size);
+	buf = read_object_file(oid, &type, &size);
 	if (!buf || type != OBJ_BLOB)
 		die("unable to read blob object %s", oid_to_hex(oid));
 
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index 6620feec68..b7755c6cc5 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -199,7 +199,7 @@ static int check_object(struct object *obj, int type, void *data, struct fsck_op
 
 	if (!(obj->flags & FLAG_OPEN)) {
 		unsigned long size;
-		int type = sha1_object_info(obj->oid.hash, &size);
+		int type = oid_object_info(&obj->oid, &size);
 		if (type != obj->type || type <= 0)
 			die("object of unexpected type");
 		obj->flags |= FLAG_WRITTEN;
@@ -423,7 +423,7 @@ static void unpack_delta_entry(enum object_type type, unsigned long delta_size,
 	if (resolve_against_held(nr, &base_oid, delta_data, delta_size))
 		return;
 
-	base = read_sha1_file(base_oid.hash, &type, &base_size);
+	base = read_object_file(&base_oid, &type, &base_size);
 	if (!base) {
 		error("failed to read delta-pack base object %s",
 		      oid_to_hex(&base_oid));
diff --git a/builtin/update-index.c b/builtin/update-index.c
index 58d1c2d282..9625d1e10a 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -592,7 +592,7 @@ static struct cache_entry *read_one_ent(const char *which,
 	int size;
 	struct cache_entry *ce;
 
-	if (get_tree_entry(ent->hash, path, oid.hash, &mode)) {
+	if (get_tree_entry(ent, path, &oid, &mode)) {
 		if (which)
 			error("%s: not in %s branch.", path, which);
 		return NULL;
diff --git a/builtin/verify-commit.c b/builtin/verify-commit.c
index 05315ea7c9..dcdaada111 100644
--- a/builtin/verify-commit.c
+++ b/builtin/verify-commit.c
@@ -44,7 +44,7 @@ static int verify_commit(const char *name, unsigned flags)
 	if (get_oid(name, &oid))
 		return error("commit '%s' not found.", name);
 
-	buf = read_sha1_file(oid.hash, &type, &size);
+	buf = read_object_file(&oid, &type, &size);
 	if (!buf)
 		return error("%s: unable to read file.", name);
 	if (type != OBJ_COMMIT)
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 670555dedd..ba2cb877c3 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -502,7 +502,7 @@ static void show_worktree(struct worktree *wt, int path_maxlen, int abbrev_len)
 		strbuf_addstr(&sb, "(bare)");
 	else {
 		strbuf_addf(&sb, "%-*s ", abbrev_len,
-				find_unique_abbrev(wt->head_oid.hash, DEFAULT_ABBREV));
+				find_unique_abbrev(&wt->head_oid, DEFAULT_ABBREV));
 		if (wt->is_detached)
 			strbuf_addstr(&sb, "(detached HEAD)");
 		else if (wt->head_ref) {
@@ -527,7 +527,7 @@ static void measure_widths(struct worktree **wt, int *abbrev, int *maxlen)
 
 		if (path_len > *maxlen)
 			*maxlen = path_len;
-		sha1_len = strlen(find_unique_abbrev(wt[i]->head_oid.hash, *abbrev));
+		sha1_len = strlen(find_unique_abbrev(&wt[i]->head_oid, *abbrev));
 		if (sha1_len > *abbrev)
 			*abbrev = sha1_len;
 	}
diff --git a/builtin/write-tree.c b/builtin/write-tree.c
index bd0a78aa3c..c9d3c544e7 100644
--- a/builtin/write-tree.c
+++ b/builtin/write-tree.c
@@ -19,7 +19,7 @@ int cmd_write_tree(int argc, const char **argv, const char *unused_prefix)
 {
 	int flags = 0, ret;
 	const char *prefix = NULL;
-	unsigned char sha1[20];
+	struct object_id oid;
 	const char *me = "git-write-tree";
 	struct option write_tree_options[] = {
 		OPT_BIT(0, "missing-ok", &flags, N_("allow missing objects"),
@@ -38,10 +38,10 @@ int cmd_write_tree(int argc, const char **argv, const char *unused_prefix)
 	argc = parse_options(argc, argv, unused_prefix, write_tree_options,
 			     write_tree_usage, 0);
 
-	ret = write_cache_as_tree(sha1, flags, prefix);
+	ret = write_cache_as_tree(&oid, flags, prefix);
 	switch (ret) {
 	case 0:
-		printf("%s\n", sha1_to_hex(sha1));
+		printf("%s\n", oid_to_hex(&oid));
 		break;
 	case WRITE_TREE_UNREADABLE_INDEX:
 		die("%s: error reading the index", me);