Merge branch 'bc/object-id'

Conversion from uchar[20] to struct object_id continues. * bc/object-id: (42 commits) merge-one-file: compute empty blob object ID add--interactive: compute the empty tree value Update shell scripts to compute empty tree object ID sha1_file: only expose empty object constants through git_hash_algo dir: use the_hash_algo for empty blob object ID sequencer: use the_hash_algo for empty tree object ID cache-tree: use is_empty_tree_oid sha1_file: convert cached object code to struct object_id builtin/reset: convert use of EMPTY_TREE_SHA1_BIN builtin/receive-pack: convert one use of EMPTY_TREE_SHA1_HEX wt-status: convert two uses of EMPTY_TREE_SHA1_HEX submodule: convert several uses of EMPTY_TREE_SHA1_HEX sequencer: convert one use of EMPTY_TREE_SHA1_HEX merge: convert empty tree constant to the_hash_algo builtin/merge: switch tree functions to use object_id builtin/am: convert uses of EMPTY_TREE_SHA1_BIN to the_hash_algo sha1-file: add functions for hex empty tree and blob OIDs builtin/receive-pack: avoid hard-coded constants for push certs diff: specify abbreviation size in terms of the_hash_algo upload-pack: replace use of several hard-coded constants ...
2024-05-09 18:26:08 +02:00 · 2018-05-30 14:04:10 +09:00 · 2018-05-30 14:04:10 +09:00 · 42c8ce1c49
parent 3d24129799 7882fa220c
commit 42c8ce1c49
46 changed files with 348 additions and 306 deletions
--- a/builtin/am.c
+++ b/builtin/am.c
@ -1542,7 +1542,7 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
 	char *their_tree_name;

 	if (get_oid("HEAD", &our_tree) < 0)
-		hashcpy(our_tree.hash, EMPTY_TREE_SHA1_BIN);
+		oidcpy(&our_tree, the_hash_algo->empty_tree);

 	if (build_fake_ancestor(state, index_path))
 		return error("could not build fake ancestor");
@ -2042,7 +2042,7 @@ static void am_skip(struct am_state *state)
 	am_rerere_clear();

 	if (get_oid("HEAD", &head))
-		hashcpy(head.hash, EMPTY_TREE_SHA1_BIN);
+		oidcpy(&head, the_hash_algo->empty_tree);

 	if (clean_index(&head, &head))
 		die(_("failed to clean index"));
@ -2105,11 +2105,11 @@ static void am_abort(struct am_state *state)
 	curr_branch = resolve_refdup("HEAD", 0, &curr_head, NULL);
 	has_curr_head = curr_branch && !is_null_oid(&curr_head);
 	if (!has_curr_head)
-		hashcpy(curr_head.hash, EMPTY_TREE_SHA1_BIN);
+		oidcpy(&curr_head, the_hash_algo->empty_tree);

 	has_orig_head = !get_oid("ORIG_HEAD", &orig_head);
 	if (!has_orig_head)
-		hashcpy(orig_head.hash, EMPTY_TREE_SHA1_BIN);
+		oidcpy(&orig_head, the_hash_algo->empty_tree);

 	clean_index(&curr_head, &orig_head);

--- a/builtin/count-objects.c
+++ b/builtin/count-objects.c
@ -66,7 +66,7 @@ static int count_loose(const struct object_id *oid, const char *path, void *data
 	else {
 		loose_size += on_disk_bytes(st);
 		loose++;
-		if (verbose && has_sha1_pack(oid->hash))
+		if (verbose && has_object_pack(oid))
 			packed_loose++;
 	}
 	return 0;
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@ -228,7 +228,7 @@ static void check_reachable_object(struct object *obj)
 	if (!(obj->flags & HAS_OBJ)) {
 		if (is_promisor_object(&obj->oid))
 			return;
-		if (has_sha1_pack(obj->oid.hash))
+		if (has_object_pack(&obj->oid))
 			return; /* it is in pack - forget about it */
 		printf("missing %s %s\n", printable_type(obj),
 			describe_object(obj));
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@ -1549,12 +1549,13 @@ static void read_v2_anomalous_offsets(struct packed_git *p,
 {
 	const uint32_t *idx1, *idx2;
 	uint32_t i;
+	const uint32_t hashwords = the_hash_algo->rawsz / sizeof(uint32_t);

 	/* The address of the 4-byte offset table */
 	idx1 = (((const uint32_t *)p->index_data)
 		+ 2 /* 8-byte header */
 		+ 256 /* fan out */
-		+ 5 * p->num_objects /* 20-byte SHA-1 table */
+		+ hashwords * p->num_objects /* object ID table */
 		+ p->num_objects /* CRC32 table */
 		);

--- a/builtin/merge.c
+++ b/builtin/merge.c
@ -280,7 +280,7 @@ static int save_state(struct object_id *stash)
 	return rc;
 }

-static void read_empty(unsigned const char *sha1, int verbose)
+static void read_empty(const struct object_id *oid, int verbose)
 {
 	int i = 0;
 	const char *args[7];
@ -290,15 +290,15 @@ static void read_empty(unsigned const char *sha1, int verbose)
 		args[i++] = "-v";
 	args[i++] = "-m";
 	args[i++] = "-u";
-	args[i++] = EMPTY_TREE_SHA1_HEX;
-	args[i++] = sha1_to_hex(sha1);
+	args[i++] = empty_tree_oid_hex();
+	args[i++] = oid_to_hex(oid);
 	args[i] = NULL;

 	if (run_command_v_opt(args, RUN_GIT_CMD))
 		die(_("read-tree failed"));
 }

-static void reset_hard(unsigned const char *sha1, int verbose)
+static void reset_hard(const struct object_id *oid, int verbose)
 {
 	int i = 0;
 	const char *args[6];
@ -308,7 +308,7 @@ static void reset_hard(unsigned const char *sha1, int verbose)
 		args[i++] = "-v";
 	args[i++] = "--reset";
 	args[i++] = "-u";
-	args[i++] = sha1_to_hex(sha1);
+	args[i++] = oid_to_hex(oid);
 	args[i] = NULL;

 	if (run_command_v_opt(args, RUN_GIT_CMD))
@ -324,7 +324,7 @@ static void restore_state(const struct object_id *head,
 	if (is_null_oid(stash))
 		return;

-	reset_hard(head->hash, 1);
+	reset_hard(head, 1);

 	args[2] = oid_to_hex(stash);

@ -1297,7 +1297,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		if (remoteheads->next)
 			die(_("Can merge only exactly one commit into empty head"));
 		remote_head_oid = &remoteheads->item->object.oid;
-		read_empty(remote_head_oid->hash, 0);
+		read_empty(remote_head_oid, 0);
 		update_ref("initial pull", "HEAD", remote_head_oid, NULL, 0,
 			   UPDATE_REFS_DIE_ON_ERR);
 		goto done;
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@ -279,6 +279,7 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 	enum object_type type;
 	void *buf;
 	struct git_istream *st = NULL;
+	const unsigned hashsz = the_hash_algo->rawsz;

 	if (!usable_delta) {
 		if (oe_type(entry) == OBJ_BLOB &&
@ -335,7 +336,7 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 		dheader[pos] = ofs & 127;
 		while (ofs >>= 7)
 			dheader[--pos] = 128 | (--ofs & 127);
-		if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit) {
+		if (limit && hdrlen + sizeof(dheader) - pos + datalen + hashsz >= limit) {
 			if (st)
 				close_istream(st);
 			free(buf);
@ -347,19 +348,19 @@ static unsigned long write_no_reuse_object(struct hashfile *f, struct object_ent
 	} else if (type == OBJ_REF_DELTA) {
 		/*
 		 * Deltas with a base reference contain
-		 * an additional 20 bytes for the base sha1.
+		 * additional bytes for the base object ID.
 		 */
-		if (limit && hdrlen + 20 + datalen + 20 >= limit) {
+		if (limit && hdrlen + hashsz + datalen + hashsz >= limit) {
 			if (st)
 				close_istream(st);
 			free(buf);
 			return 0;
 		}
 		hashwrite(f, header, hdrlen);
-		hashwrite(f, DELTA(entry)->idx.oid.hash, 20);
-		hdrlen += 20;
+		hashwrite(f, DELTA(entry)->idx.oid.hash, hashsz);
+		hdrlen += hashsz;
 	} else {
-		if (limit && hdrlen + datalen + 20 >= limit) {
+		if (limit && hdrlen + datalen + hashsz >= limit) {
 			if (st)
 				close_istream(st);
 			free(buf);
@ -391,6 +392,7 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 	unsigned char header[MAX_PACK_OBJECT_HEADER],
 		      dheader[MAX_PACK_OBJECT_HEADER];
 	unsigned hdrlen;
+	const unsigned hashsz = the_hash_algo->rawsz;
 	unsigned long entry_size = SIZE(entry);

 	if (DELTA(entry))
@ -427,7 +429,7 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 		dheader[pos] = ofs & 127;
 		while (ofs >>= 7)
 			dheader[--pos] = 128 | (--ofs & 127);
-		if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit) {
+		if (limit && hdrlen + sizeof(dheader) - pos + datalen + hashsz >= limit) {
 			unuse_pack(&w_curs);
 			return 0;
 		}
@ -436,16 +438,16 @@ static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
 		hdrlen += sizeof(dheader) - pos;
 		reused_delta++;
 	} else if (type == OBJ_REF_DELTA) {
-		if (limit && hdrlen + 20 + datalen + 20 >= limit) {
+		if (limit && hdrlen + hashsz + datalen + hashsz >= limit) {
 			unuse_pack(&w_curs);
 			return 0;
 		}
 		hashwrite(f, header, hdrlen);
-		hashwrite(f, DELTA(entry)->idx.oid.hash, 20);
-		hdrlen += 20;
+		hashwrite(f, DELTA(entry)->idx.oid.hash, hashsz);
+		hdrlen += hashsz;
 		reused_delta++;
 	} else {
-		if (limit && hdrlen + datalen + 20 >= limit) {
+		if (limit && hdrlen + datalen + hashsz >= limit) {
 			unuse_pack(&w_curs);
 			return 0;
 		}
@ -769,7 +771,7 @@ static off_t write_reused_pack(struct hashfile *f)
 		die_errno("unable to seek in reused packfile");

 	if (reuse_packfile_offset < 0)
-		reuse_packfile_offset = reuse_packfile->pack_size - 20;
+		reuse_packfile_offset = reuse_packfile->pack_size - the_hash_algo->rawsz;

 	total = to_write = reuse_packfile_offset - sizeof(struct pack_header);

@ -1033,7 +1035,7 @@ static int want_object_in_pack(const struct object_id *oid,
 	int want;
 	struct list_head *pos;

-	if (!exclude && local && has_loose_object_nonlocal(oid->hash))
+	if (!exclude && local && has_loose_object_nonlocal(oid))
 		return 0;

 	/*
@ -1467,7 +1469,7 @@ static void check_object(struct object_entry *entry)
 			if (reuse_delta && !entry->preferred_base)
 				base_ref = use_pack(p, &w_curs,
 						entry->in_pack_offset + used, NULL);
-			entry->in_pack_header_size = used + 20;
+			entry->in_pack_header_size = used + the_hash_algo->rawsz;
 			break;
 		case OBJ_OFS_DELTA:
 			buf = use_pack(p, &w_curs,
@ -1949,7 +1951,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	/* Now some size filtering heuristics. */
 	trg_size = SIZE(trg_entry);
 	if (!DELTA(trg_entry)) {
-		max_size = trg_size/2 - 20;
+		max_size = trg_size/2 - the_hash_algo->rawsz;
 		ref_depth = 1;
 	} else {
 		max_size = DELTA_SIZE(trg_entry);
--- a/builtin/pack-redundant.c
+++ b/builtin/pack-redundant.c
@ -20,7 +20,7 @@ static int load_all_packs, verbose, alt_odb;

 struct llist_item {
 	struct llist_item *next;
-	const unsigned char *sha1;
+	const struct object_id *oid;
 };
 static struct llist {
 	struct llist_item *front;
@ -90,14 +90,14 @@ static struct llist * llist_copy(struct llist *list)
 		return ret;

 	new_item = ret->front = llist_item_get();
-	new_item->sha1 = list->front->sha1;
+	new_item->oid = list->front->oid;

 	old_item = list->front->next;
 	while (old_item) {
 		prev = new_item;
 		new_item = llist_item_get();
 		prev->next = new_item;
-		new_item->sha1 = old_item->sha1;
+		new_item->oid = old_item->oid;
 		old_item = old_item->next;
 	}
 	new_item->next = NULL;
@ -108,10 +108,10 @@ static struct llist * llist_copy(struct llist *list)

 static inline struct llist_item *llist_insert(struct llist *list,
 					      struct llist_item *after,
-					       const unsigned char *sha1)
+					      const struct object_id *oid)
 {
 	struct llist_item *new_item = llist_item_get();
-	new_item->sha1 = sha1;
+	new_item->oid = oid;
 	new_item->next = NULL;

 	if (after != NULL) {
@ -131,21 +131,21 @@ static inline struct llist_item *llist_insert(struct llist *list,
 }

 static inline struct llist_item *llist_insert_back(struct llist *list,
-						   const unsigned char *sha1)
+						   const struct object_id *oid)
 {
-	return llist_insert(list, list->back, sha1);
+	return llist_insert(list, list->back, oid);
 }

 static inline struct llist_item *llist_insert_sorted_unique(struct llist *list,
-			const unsigned char *sha1, struct llist_item *hint)
+			const struct object_id *oid, struct llist_item *hint)
 {
 	struct llist_item *prev = NULL, *l;

 	l = (hint == NULL) ? list->front : hint;
 	while (l) {
-		int cmp = hashcmp(l->sha1, sha1);
+		int cmp = oidcmp(l->oid, oid);
 		if (cmp > 0) { /* we insert before this entry */
-			return llist_insert(list, prev, sha1);
+			return llist_insert(list, prev, oid);
 		}
 		if (!cmp) { /* already exists */
 			return l;
@ -154,11 +154,11 @@ static inline struct llist_item *llist_insert_sorted_unique(struct llist *list,
 		l = l->next;
 	}
 	/* insert at the end */
-	return llist_insert_back(list, sha1);
+	return llist_insert_back(list, oid);
 }

 /* returns a pointer to an item in front of sha1 */
-static inline struct llist_item * llist_sorted_remove(struct llist *list, const unsigned char *sha1, struct llist_item *hint)
+static inline struct llist_item * llist_sorted_remove(struct llist *list, const struct object_id *oid, struct llist_item *hint)
 {
 	struct llist_item *prev, *l;

@ -166,7 +166,7 @@ static inline struct llist_item * llist_sorted_remove(struct llist *list, const
 	l = (hint == NULL) ? list->front : hint;
 	prev = NULL;
 	while (l) {
-		int cmp = hashcmp(l->sha1, sha1);
+		int cmp = oidcmp(l->oid, oid);
 		if (cmp > 0) /* not in list, since sorted */
 			return prev;
 		if (!cmp) { /* found */
@ -201,7 +201,7 @@ static void llist_sorted_difference_inplace(struct llist *A,
 	b = B->front;

 	while (b) {
-		hint = llist_sorted_remove(A, b->sha1, hint);
+		hint = llist_sorted_remove(A, b->oid, hint);
 		b = b->next;
 	}
 }
@ -252,13 +252,14 @@ static void cmp_two_packs(struct pack_list *p1, struct pack_list *p2)
 	unsigned long p1_off = 0, p2_off = 0, p1_step, p2_step;
 	const unsigned char *p1_base, *p2_base;
 	struct llist_item *p1_hint = NULL, *p2_hint = NULL;
+	const unsigned int hashsz = the_hash_algo->rawsz;

 	p1_base = p1->pack->index_data;
 	p2_base = p2->pack->index_data;
 	p1_base += 256 * 4 + ((p1->pack->index_version < 2) ? 4 : 8);
 	p2_base += 256 * 4 + ((p2->pack->index_version < 2) ? 4 : 8);
-	p1_step = (p1->pack->index_version < 2) ? 24 : 20;
-	p2_step = (p2->pack->index_version < 2) ? 24 : 20;
+	p1_step = hashsz + ((p1->pack->index_version < 2) ? 4 : 0);
+	p2_step = hashsz + ((p2->pack->index_version < 2) ? 4 : 0);

 	while (p1_off < p1->pack->num_objects * p1_step &&
 	       p2_off < p2->pack->num_objects * p2_step)
@ -267,9 +268,11 @@ static void cmp_two_packs(struct pack_list *p1, struct pack_list *p2)
 		/* cmp ~ p1 - p2 */
 		if (cmp == 0) {
 			p1_hint = llist_sorted_remove(p1->unique_objects,
-					p1_base + p1_off, p1_hint);
+					(const struct object_id *)(p1_base + p1_off),
+					p1_hint);
 			p2_hint = llist_sorted_remove(p2->unique_objects,
-					p1_base + p1_off, p2_hint);
+					(const struct object_id *)(p1_base + p1_off),
+					p2_hint);
 			p1_off += p1_step;
 			p2_off += p2_step;
 			continue;
@ -359,13 +362,14 @@ static size_t sizeof_union(struct packed_git *p1, struct packed_git *p2)
 	size_t ret = 0;
 	unsigned long p1_off = 0, p2_off = 0, p1_step, p2_step;
 	const unsigned char *p1_base, *p2_base;
+	const unsigned int hashsz = the_hash_algo->rawsz;

 	p1_base = p1->index_data;
 	p2_base = p2->index_data;
 	p1_base += 256 * 4 + ((p1->index_version < 2) ? 4 : 8);
 	p2_base += 256 * 4 + ((p2->index_version < 2) ? 4 : 8);
-	p1_step = (p1->index_version < 2) ? 24 : 20;
-	p2_step = (p2->index_version < 2) ? 24 : 20;
+	p1_step = hashsz + ((p1->index_version < 2) ? 4 : 0);
+	p2_step = hashsz + ((p2->index_version < 2) ? 4 : 0);

 	while (p1_off < p1->num_objects * p1_step &&
 	       p2_off < p2->num_objects * p2_step)
@ -499,7 +503,7 @@ static void load_all_objects(void)
 		l = pl->all_objects->front;
 		while (l) {
 			hint = llist_insert_sorted_unique(all_objects,
-							  l->sha1, hint);
+							  l->oid, hint);
 			l = l->next;
 		}
 		pl = pl->next;
@ -558,9 +562,9 @@ static struct pack_list * add_pack(struct packed_git *p)

 	base = p->index_data;
 	base += 256 * 4 + ((p->index_version < 2) ? 4 : 8);
-	step = (p->index_version < 2) ? 24 : 20;
+	step = the_hash_algo->rawsz + ((p->index_version < 2) ? 4 : 0);
 	while (off < p->num_objects * step) {
-		llist_insert_back(l.all_objects, base + off);
+		llist_insert_back(l.all_objects, (const struct object_id *)(base + off));
 		off += step;
 	}
 	/* this list will be pruned in cmp_two_packs later */
@ -601,8 +605,8 @@ int cmd_pack_redundant(int argc, const char **argv, const char *prefix)
 	int i;
 	struct pack_list *min, *red, *pl;
 	struct llist *ignore;
-	unsigned char *sha1;
-	char buf[42]; /* 40 byte sha1 + \n + \0 */
+	struct object_id *oid;
+	char buf[GIT_MAX_HEXSZ + 2]; /* hex hash + \n + \0 */

 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage(pack_redundant_usage);
@ -650,10 +654,10 @@ int cmd_pack_redundant(int argc, const char **argv, const char *prefix)
 	llist_init(&ignore);
 	if (!isatty(0)) {
 		while (fgets(buf, sizeof(buf), stdin)) {
-			sha1 = xmalloc(20);
-			if (get_sha1_hex(buf, sha1))
-				die("Bad sha1 on stdin: %s", buf);
-			llist_insert_sorted_unique(ignore, sha1, NULL);
+			oid = xmalloc(sizeof(*oid));
+			if (get_oid_hex(buf, oid))
+				die("Bad object ID on stdin: %s", buf);
+			llist_insert_sorted_unique(ignore, oid, NULL);
 		}
 	}
 	llist_sorted_difference_inplace(all_objects, ignore);
--- a/builtin/prune-packed.c
+++ b/builtin/prune-packed.c
@ -25,7 +25,7 @@ static int prune_object(const struct object_id *oid, const char *path,
 {
 	int *opts = data;

-	if (!has_sha1_pack(oid->hash))
+	if (!has_object_pack(oid))
 		return 0;

 	if (*opts & PRUNE_PACKED_DRY_RUN)
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@ -454,21 +454,21 @@ static void hmac_sha1(unsigned char *out,
 	/* RFC 2104 2. (6) & (7) */
 	git_SHA1_Init(&ctx);
 	git_SHA1_Update(&ctx, k_opad, sizeof(k_opad));
-	git_SHA1_Update(&ctx, out, 20);
+	git_SHA1_Update(&ctx, out, GIT_SHA1_RAWSZ);
 	git_SHA1_Final(out, &ctx);
 }

 static char *prepare_push_cert_nonce(const char *path, timestamp_t stamp)
 {
 	struct strbuf buf = STRBUF_INIT;
-	unsigned char sha1[20];
+	unsigned char sha1[GIT_SHA1_RAWSZ];

 	strbuf_addf(&buf, "%s:%"PRItime, path, stamp);
 	hmac_sha1(sha1, buf.buf, buf.len, cert_nonce_seed, strlen(cert_nonce_seed));;
 	strbuf_release(&buf);

 	/* RFC 2104 5. HMAC-SHA1-80 */
-	strbuf_addf(&buf, "%"PRItime"-%.*s", stamp, 20, sha1_to_hex(sha1));
+	strbuf_addf(&buf, "%"PRItime"-%.*s", stamp, GIT_SHA1_HEXSZ, sha1_to_hex(sha1));
 	return strbuf_detach(&buf, NULL);
 }

@ -968,7 +968,7 @@ static const char *push_to_deploy(unsigned char *sha1,
 		return "Working directory has unstaged changes";

 	/* diff-index with either HEAD or an empty tree */
-	diff_index[4] = head_has_history() ? "HEAD" : EMPTY_TREE_SHA1_HEX;
+	diff_index[4] = head_has_history() ? "HEAD" : empty_tree_oid_hex();

 	child_process_init(&child);
 	child.argv = diff_index;
--- a/builtin/reset.c
+++ b/builtin/reset.c
@ -314,7 +314,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 	unborn = !strcmp(rev, "HEAD") && get_oid("HEAD", &oid);
 	if (unborn) {
 		/* reset on unborn branch: treat as reset to empty tree */
-		hashcpy(oid.hash, EMPTY_TREE_SHA1_BIN);
+		oidcpy(&oid, the_hash_algo->empty_tree);
 	} else if (!pathspec.nr) {
 		struct commit *commit;
 		if (get_oid_committish(rev, &oid))
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@ -887,8 +887,8 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				if (read_cache() < 0)
 					die(_("Could not read the index"));
 				if (the_index.split_index) {
-					const unsigned char *sha1 = the_index.split_index->base_sha1;
-					const char *path = git_path("sharedindex.%s", sha1_to_hex(sha1));
+					const struct object_id *oid = &the_index.split_index->base_oid;
+					const char *path = git_path("sharedindex.%s", oid_to_hex(oid));
 					strbuf_reset(&buf);
 					puts(relative_path(path, prefix, &buf));
 				}
--- a/cache-tree.c
+++ b/cache-tree.c
@ -385,7 +385,7 @@ static int update_one(struct cache_tree *it,
 		/*
 		 * "sub" can be an empty tree if all subentries are i-t-a.
 		 */
-		if (contains_ita && !oidcmp(oid, &empty_tree_oid))
+		if (contains_ita && is_empty_tree_oid(oid))
 			continue;

 		strbuf_grow(&buffer, entlen + 100);
@ -523,7 +523,7 @@ static struct cache_tree *read_one(const char **buffer, unsigned long *size_p)
 	if (0 <= it->entry_count) {
 		if (size < rawsz)
 			goto free_return;
-		memcpy(it->oid.hash, (const unsigned char*)buf, rawsz);
+		oidread(&it->oid, (const unsigned char *)buf);
 		buf += rawsz;
 		size -= rawsz;
 	}
--- a/cache.h
+++ b/cache.h
@ -324,7 +324,7 @@ struct index_state {
 		 drop_cache_tree : 1;
 	struct hashmap name_hash;
 	struct hashmap dir_hash;
-	unsigned char sha1[20];
+	struct object_id oid;
 	struct untracked_cache *untracked;
 	uint64_t fsmonitor_last_update;
 	struct ewah_bitmap *fsmonitor_dirty;
@ -1017,21 +1017,10 @@ static inline void oidclr(struct object_id *oid)
 	memset(oid->hash, 0, GIT_MAX_RAWSZ);
 }

-
-#define EMPTY_TREE_SHA1_HEX \
-	"4b825dc642cb6eb9a060e54bf8d69288fbee4904"
-#define EMPTY_TREE_SHA1_BIN_LITERAL \
-	 "\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60" \
-	 "\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04"
-extern const struct object_id empty_tree_oid;
-#define EMPTY_TREE_SHA1_BIN (empty_tree_oid.hash)
-
-#define EMPTY_BLOB_SHA1_HEX \
-	"e69de29bb2d1d6434b8b29ae775ad8c2e48c5391"
-#define EMPTY_BLOB_SHA1_BIN_LITERAL \
-	"\xe6\x9d\xe2\x9b\xb2\xd1\xd6\x43\x4b\x8b" \
-	"\x29\xae\x77\x5a\xd8\xc2\xe4\x8c\x53\x91"
-extern const struct object_id empty_blob_oid;
+static inline void oidread(struct object_id *oid, const unsigned char *hash)
+{
+	memcpy(oid->hash, hash, the_hash_algo->rawsz);
+}

 static inline int is_empty_blob_sha1(const unsigned char *sha1)
 {
@ -1053,6 +1042,9 @@ static inline int is_empty_tree_oid(const struct object_id *oid)
 	return !oidcmp(oid, the_hash_algo->empty_tree);
 }

+const char *empty_tree_oid_hex(void);
+const char *empty_blob_oid_hex(void);
+
 /* set default permissions by passing mode arguments to open(2) */
 int git_mkstemps_mode(char *pattern, int suffix_len, int mode);
 int git_mkstemp_mode(char *pattern, int mode);
@ -1268,7 +1260,7 @@ extern int has_object_file_with_flags(const struct object_id *oid, int flags);
 * with the specified name.  This function does not respect replace
 * references.
 */
-extern int has_loose_object_nonlocal(const unsigned char *sha1);
+extern int has_loose_object_nonlocal(const struct object_id *oid);

 extern void assert_oid_type(const struct object_id *oid, enum object_type expect);

@ -1299,7 +1291,6 @@ static inline int hex2chr(const char *s)
 #define FALLBACK_DEFAULT_ABBREV 7

 struct object_context {
-	unsigned char tree[20];
 	unsigned mode;
 	/*
 	 * symlink_path is only used by get_tree_entry_follow_symlinks,
@ -1566,7 +1557,6 @@ struct pack_window {

 struct pack_entry {
 	off_t offset;
-	unsigned char sha1[20];
 	struct packed_git *p;
 };

--- a/commit.c
+++ b/commit.c
@ -358,7 +358,7 @@ int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long s
 	if (tail <= bufptr + tree_entry_len + 1 || memcmp(bufptr, "tree ", 5) ||
 			bufptr[tree_entry_len] != '\n')
 		return error("bogus commit object %s", oid_to_hex(&item->object.oid));
-	if (get_sha1_hex(bufptr + 5, parent.hash) < 0)
+	if (get_oid_hex(bufptr + 5, &parent) < 0)
 		return error("bad tree pointer in commit %s",
 			     oid_to_hex(&item->object.oid));
 	item->maybe_tree = lookup_tree(&parent);
@ -370,7 +370,7 @@ int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long s
 		struct commit *new_parent;

 		if (tail <= bufptr + parent_entry_len + 1 ||
-		    get_sha1_hex(bufptr + 7, parent.hash) ||
+		    get_oid_hex(bufptr + 7, &parent) ||
 		    bufptr[parent_entry_len] != '\n')
 			return error("bad parents in commit %s", oid_to_hex(&item->object.oid));
 		bufptr += parent_entry_len + 1;
--- a/diff.c
+++ b/diff.c
@ -3472,7 +3472,7 @@ static int reuse_worktree_file(const char *name, const struct object_id *oid, in
 	 * 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(oid->hash))
+	if (!FAST_WORKING_DIRECTORY && !want_file && has_object_pack(oid))
 		return 0;

 	/*
@ -3898,13 +3898,14 @@ static void fill_metainfo(struct strbuf *msg,
 		*must_show_header = 0;
 	}
 	if (one && two && oidcmp(&one->oid, &two->oid)) {
-		int abbrev = o->flags.full_index ? 40 : DEFAULT_ABBREV;
+		const unsigned hexsz = the_hash_algo->hexsz;
+		int abbrev = o->flags.full_index ? hexsz : DEFAULT_ABBREV;

 		if (o->flags.binary) {
 			mmfile_t mf;
 			if ((!fill_mmfile(&mf, one) && diff_filespec_is_binary(one)) ||
 			    (!fill_mmfile(&mf, two) && diff_filespec_is_binary(two)))
-				abbrev = 40;
+				abbrev = hexsz;
 		}
 		strbuf_addf(msg, "%s%sindex %s..%s", line_prefix, set,
 			    diff_abbrev_oid(&one->oid, abbrev),
@ -4139,6 +4140,11 @@ void diff_setup_done(struct diff_options *options)
 			      DIFF_FORMAT_NAME_STATUS |
 			      DIFF_FORMAT_CHECKDIFF |
 			      DIFF_FORMAT_NO_OUTPUT;
+	/*
+	 * This must be signed because we're comparing against a potentially
+	 * negative value.
+	 */
+	const int hexsz = the_hash_algo->hexsz;

 	if (options->set_default)
 		options->set_default(options);
@ -4219,8 +4225,8 @@ void diff_setup_done(struct diff_options *options)
 			 */
 			read_cache();
 	}
-	if (40 < options->abbrev)
-		options->abbrev = 40; /* full */
+	if (hexsz < options->abbrev)
+		options->abbrev = hexsz; /* full */

 	/*
 	 * It does not make sense to show the first hit we happened
@ -4798,8 +4804,8 @@ int diff_opt_parse(struct diff_options *options,
 		options->abbrev = strtoul(arg, NULL, 10);
 		if (options->abbrev < MINIMUM_ABBREV)
 			options->abbrev = MINIMUM_ABBREV;
-		else if (40 < options->abbrev)
-			options->abbrev = 40;
+		else if (the_hash_algo->hexsz < options->abbrev)
+			options->abbrev = the_hash_algo->hexsz;
 	}
 	else if ((argcount = parse_long_opt("src-prefix", av, &optarg))) {
 		options->a_prefix = optarg;
--- a/dir.c
+++ b/dir.c
@ -829,7 +829,7 @@ static int add_excludes(const char *fname, const char *base, int baselen,
 		if (size == 0) {
 			if (oid_stat) {
 				fill_stat_data(&oid_stat->stat, &st);
-				oidcpy(&oid_stat->oid, &empty_blob_oid);
+				oidcpy(&oid_stat->oid, the_hash_algo->empty_blob);
 				oid_stat->valid = 1;
 			}
 			close(fd);
@ -1241,11 +1241,11 @@ static void prep_exclude(struct dir_struct *dir,
 		    (!untracked || !untracked->valid ||
 		     /*
 		      * .. and .gitignore does not exist before
-		      * (i.e. null exclude_sha1). Then we can skip
+		      * (i.e. null exclude_oid). Then we can skip
 		      * loading .gitignore, which would result in
 		      * ENOENT anyway.
 		      */
-		     !is_null_sha1(untracked->exclude_sha1))) {
+		     !is_null_oid(&untracked->exclude_oid))) {
 			/*
 			 * dir->basebuf gets reused by the traversal, but we
 			 * need fname to remain unchanged to ensure the src
@ -1276,9 +1276,9 @@ static void prep_exclude(struct dir_struct *dir,
 		 * order, though, if you do that.
 		 */
 		if (untracked &&
-		    hashcmp(oid_stat.oid.hash, untracked->exclude_sha1)) {
+		    oidcmp(&oid_stat.oid, &untracked->exclude_oid)) {
 			invalidate_gitignore(dir->untracked, untracked);
-			hashcpy(untracked->exclude_sha1, oid_stat.oid.hash);
+			oidcpy(&untracked->exclude_oid, &oid_stat.oid);
 		}
 		dir->exclude_stack = stk;
 		current = stk->baselen;
@ -2623,9 +2623,10 @@ static void write_one_dir(struct untracked_cache_dir *untracked,
 		stat_data_to_disk(&stat_data, &untracked->stat_data);
 		strbuf_add(&wd->sb_stat, &stat_data, sizeof(stat_data));
 	}
-	if (!is_null_sha1(untracked->exclude_sha1)) {
+	if (!is_null_oid(&untracked->exclude_oid)) {
 		ewah_set(wd->sha1_valid, i);
-		strbuf_add(&wd->sb_sha1, untracked->exclude_sha1, 20);
+		strbuf_add(&wd->sb_sha1, untracked->exclude_oid.hash,
+			   the_hash_algo->rawsz);
 	}

 	intlen = encode_varint(untracked->untracked_nr, intbuf);
@ -2826,16 +2827,16 @@ static void read_stat(size_t pos, void *cb)
 	ud->valid = 1;
 }

-static void read_sha1(size_t pos, void *cb)
+static void read_oid(size_t pos, void *cb)
 {
 	struct read_data *rd = cb;
 	struct untracked_cache_dir *ud = rd->ucd[pos];
-	if (rd->data + 20 > rd->end) {
+	if (rd->data + the_hash_algo->rawsz > rd->end) {
 		rd->data = rd->end + 1;
 		return;
 	}
-	hashcpy(ud->exclude_sha1, rd->data);
-	rd->data += 20;
+	hashcpy(ud->exclude_oid.hash, rd->data);
+	rd->data += the_hash_algo->rawsz;
 }

 static void load_oid_stat(struct oid_stat *oid_stat, const unsigned char *data,
@ -2918,7 +2919,7 @@ struct untracked_cache *read_untracked_extension(const void *data, unsigned long
 	ewah_each_bit(rd.check_only, set_check_only, &rd);
 	rd.data = next + len;
 	ewah_each_bit(rd.valid, read_stat, &rd);
-	ewah_each_bit(rd.sha1_valid, read_sha1, &rd);
+	ewah_each_bit(rd.sha1_valid, read_oid, &rd);
 	next = rd.data;

 done:
--- a/dir.h
+++ b/dir.h
@ -3,6 +3,7 @@

 /* See Documentation/technical/api-directory-listing.txt */

+#include "cache.h"
 #include "strbuf.h"

 struct dir_entry {
@ -118,8 +119,8 @@ struct untracked_cache_dir {
 	/* all data except 'dirs' in this struct are good */
 	unsigned int valid : 1;
 	unsigned int recurse : 1;
-	/* null SHA-1 means this directory does not have .gitignore */
-	unsigned char exclude_sha1[20];
+	/* null object ID means this directory does not have .gitignore */
+	struct object_id exclude_oid;
 	char name[FLEX_ARRAY];
 };

--- a/fsck.c
+++ b/fsck.c
@ -734,30 +734,31 @@ static int fsck_ident(const char **ident, struct object *obj, struct fsck_option
 static int fsck_commit_buffer(struct commit *commit, const char *buffer,
 	unsigned long size, struct fsck_options *options)
 {
-	unsigned char tree_sha1[20], sha1[20];
+	struct object_id tree_oid, oid;
 	struct commit_graft *graft;
 	unsigned parent_count, parent_line_count = 0, author_count;
 	int err;
 	const char *buffer_begin = buffer;
+	const char *p;

 	if (verify_headers(buffer, size, &commit->object, options))
 		return -1;

 	if (!skip_prefix(buffer, "tree ", &buffer))
 		return report(options, &commit->object, FSCK_MSG_MISSING_TREE, "invalid format - expected 'tree' line");
-	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n') {
+	if (parse_oid_hex(buffer, &tree_oid, &p) || *p != '\n') {
 		err = report(options, &commit->object, FSCK_MSG_BAD_TREE_SHA1, "invalid 'tree' line format - bad sha1");
 		if (err)
 			return err;
 	}
-	buffer += 41;
+	buffer = p + 1;
 	while (skip_prefix(buffer, "parent ", &buffer)) {
-		if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n') {
+		if (parse_oid_hex(buffer, &oid, &p) || *p != '\n') {
 			err = report(options, &commit->object, FSCK_MSG_BAD_PARENT_SHA1, "invalid 'parent' line format - bad sha1");
 			if (err)
 				return err;
 		}
-		buffer += 41;
+		buffer = p + 1;
 		parent_line_count++;
 	}
 	graft = lookup_commit_graft(&commit->object.oid);
@ -796,7 +797,7 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
 	if (err)
 		return err;
 	if (!get_commit_tree(commit)) {
-		err = report(options, &commit->object, FSCK_MSG_BAD_TREE, "could not load commit's tree %s", sha1_to_hex(tree_sha1));
+		err = report(options, &commit->object, FSCK_MSG_BAD_TREE, "could not load commit's tree %s", oid_to_hex(&tree_oid));
 		if (err)
 			return err;
 	}
@ -822,11 +823,12 @@ static int fsck_commit(struct commit *commit, const char *data,
 static int fsck_tag_buffer(struct tag *tag, const char *data,
 	unsigned long size, struct fsck_options *options)
 {
-	unsigned char sha1[20];
+	struct object_id oid;
 	int ret = 0;
 	const char *buffer;
 	char *to_free = NULL, *eol;
 	struct strbuf sb = STRBUF_INIT;
+	const char *p;

 	if (data)
 		buffer = data;
@ -857,12 +859,12 @@ static int fsck_tag_buffer(struct tag *tag, const char *data,
 		ret = report(options, &tag->object, FSCK_MSG_MISSING_OBJECT, "invalid format - expected 'object' line");
 		goto done;
 	}
-	if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n') {
+	if (parse_oid_hex(buffer, &oid, &p) || *p != '\n') {
 		ret = report(options, &tag->object, FSCK_MSG_BAD_OBJECT_SHA1, "invalid 'object' line format - bad sha1");
 		if (ret)
 			goto done;
 	}
-	buffer += 41;
+	buffer = p + 1;

 	if (!skip_prefix(buffer, "type ", &buffer)) {
 		ret = report(options, &tag->object, FSCK_MSG_MISSING_TYPE_ENTRY, "invalid format - expected 'type' line");
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@ -205,8 +205,15 @@ sub list_untracked {
 	}
 }

-sub get_empty_tree {
-	return '4b825dc642cb6eb9a060e54bf8d69288fbee4904';
+{
+	my $empty_tree;
+	sub get_empty_tree {
+		return $empty_tree if defined $empty_tree;
+
+		$empty_tree = run_cmd_pipe(qw(git hash-object -t tree /dev/null));
+		chomp $empty_tree;
+		return $empty_tree;
+	}
 }

 sub get_diff_reference {
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@ -11,6 +11,8 @@
 # The following functions will also be available in the commit filter:

 functions=$(cat << \EOF
+EMPTY_TREE=$(git hash-object -t tree /dev/null)
+
 warn () {
 	echo "$*" >&2
 }
@ -46,7 +48,7 @@ git_commit_non_empty_tree()
 {
 	if test $# = 3 && test "$1" = $(git rev-parse "$3^{tree}"); then
 		map "$3"
-	elif test $# = 1 && test "$1" = 4b825dc642cb6eb9a060e54bf8d69288fbee4904; then
+	elif test $# = 1 && test "$1" = $EMPTY_TREE; then
 		:
 	else
 		git commit-tree "$@"
--- a/git-merge-one-file.sh
+++ b/git-merge-one-file.sh
@ -120,7 +120,7 @@ case "${1:-.}${2:-.}${3:-.}" in
 	case "$1" in
 	'')
 		echo "Added $4 in both, but differently."
-		orig=$(git unpack-file e69de29bb2d1d6434b8b29ae775ad8c2e48c5391)
+		orig=$(git unpack-file $(git hash-object /dev/null))
 		;;
 	*)
 		echo "Auto-merging $4"
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@ -81,6 +81,8 @@ rewritten_pending="$state_dir"/rewritten-pending
 # and leaves CR at the end instead.
 cr=$(printf "\015")

+empty_tree=$(git hash-object -t tree /dev/null)
+
 strategy_args=${strategy:+--strategy=$strategy}
 test -n "$strategy_opts" &&
 eval '
@ -244,7 +246,7 @@ is_empty_commit() {
 		die "$(eval_gettext "\$sha1: not a commit that can be picked")"
 	}
 	ptree=$(git rev-parse -q --verify "$1"^^{tree} 2>/dev/null) ||
-		ptree=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+		ptree=$empty_tree
 	test "$tree" = "$ptree"
 }

--- a/http.c
+++ b/http.c
@ -2038,7 +2038,8 @@ int http_get_info_packs(const char *base_url, struct packed_git **packs_head)
 	int ret = 0, i = 0;
 	char *url, *data;
 	struct strbuf buf = STRBUF_INIT;
-	unsigned char sha1[20];
+	unsigned char hash[GIT_MAX_RAWSZ];
+	const unsigned hexsz = the_hash_algo->hexsz;

 	end_url_with_slash(&buf, base_url);
 	strbuf_addstr(&buf, "objects/info/packs");
@ -2054,13 +2055,13 @@ int http_get_info_packs(const char *base_url, struct packed_git **packs_head)
 		switch (data[i]) {
 		case 'P':
 			i++;
-			if (i + 52 <= buf.len &&
+			if (i + hexsz + 12 <= buf.len &&
 			    starts_with(data + i, " pack-") &&
-			    starts_with(data + i + 46, ".pack\n")) {
-				get_sha1_hex(data + i + 6, sha1);
-				fetch_and_setup_pack_index(packs_head, sha1,
+			    starts_with(data + i + hexsz + 6, ".pack\n")) {
+				get_sha1_hex(data + i + 6, hash);
+				fetch_and_setup_pack_index(packs_head, hash,
 						      base_url);
-				i += 51;
+				i += hexsz + 11;
 				break;
 			}
 		default:
--- a/merge.c
+++ b/merge.c
@ -11,10 +11,7 @@

 static const char *merge_argument(struct commit *commit)
 {
-	if (commit)
-		return oid_to_hex(&commit->object.oid);
-	else
-		return EMPTY_TREE_SHA1_HEX;
+	return oid_to_hex(commit ? &commit->object.oid : the_hash_algo->empty_tree);
 }

 int index_has_changes(struct strbuf *sb)
--- a/packfile.c
+++ b/packfile.c
@ -84,6 +84,7 @@ static int check_packed_git_idx(const char *path, struct packed_git *p)
 	uint32_t version, nr, i, *index;
 	int fd = git_open(path);
 	struct stat st;
+	const unsigned int hashsz = the_hash_algo->rawsz;

 	if (fd < 0)
 		return -1;
@ -92,7 +93,7 @@ static int check_packed_git_idx(const char *path, struct packed_git *p)
 		return -1;
 	}
 	idx_size = xsize_t(st.st_size);
-	if (idx_size < 4 * 256 + 20 + 20) {
+	if (idx_size < 4 * 256 + hashsz + hashsz) {
 		close(fd);
 		return error("index file %s is too small", path);
 	}
@ -129,11 +130,11 @@ static int check_packed_git_idx(const char *path, struct packed_git *p)
 		/*
 		 * Total size:
 		 *  - 256 index entries 4 bytes each
-		 *  - 24-byte entries * nr (20-byte sha1 + 4-byte offset)
-		 *  - 20-byte SHA1 of the packfile
-		 *  - 20-byte SHA1 file checksum
+		 *  - 24-byte entries * nr (object ID + 4-byte offset)
+		 *  - hash of the packfile
+		 *  - file checksum
 		 */
-		if (idx_size != 4*256 + nr * 24 + 20 + 20) {
+		if (idx_size != 4*256 + nr * (hashsz + 4) + hashsz + hashsz) {
 			munmap(idx_map, idx_size);
 			return error("wrong index v1 file size in %s", path);
 		}
@ -142,16 +143,16 @@ static int check_packed_git_idx(const char *path, struct packed_git *p)
 		 * Minimum size:
 		 *  - 8 bytes of header
 		 *  - 256 index entries 4 bytes each
-		 *  - 20-byte sha1 entry * nr
+		 *  - object ID entry * nr
 		 *  - 4-byte crc entry * nr
 		 *  - 4-byte offset entry * nr
-		 *  - 20-byte SHA1 of the packfile
-		 *  - 20-byte SHA1 file checksum
+		 *  - hash of the packfile
+		 *  - file checksum
 		 * And after the 4-byte offset table might be a
 		 * variable sized table containing 8-byte entries
 		 * for offsets larger than 2^31.
 		 */
-		unsigned long min_size = 8 + 4*256 + nr*(20 + 4 + 4) + 20 + 20;
+		unsigned long min_size = 8 + 4*256 + nr*(hashsz + 4 + 4) + hashsz + hashsz;
 		unsigned long max_size = min_size;
 		if (nr)
 			max_size += (nr - 1)*8;
@ -444,10 +445,11 @@ static int open_packed_git_1(struct packed_git *p)
 {
 	struct stat st;
 	struct pack_header hdr;
-	unsigned char sha1[20];
-	unsigned char *idx_sha1;
+	unsigned char hash[GIT_MAX_RAWSZ];
+	unsigned char *idx_hash;
 	long fd_flag;
 	ssize_t read_result;
+	const unsigned hashsz = the_hash_algo->rawsz;

 	if (!p->index_data && open_pack_index(p))
 		return error("packfile %s index unavailable", p->pack_name);
@ -507,15 +509,15 @@ static int open_packed_git_1(struct packed_git *p)
 			     " while index indicates %"PRIu32" objects",
 			     p->pack_name, ntohl(hdr.hdr_entries),
 			     p->num_objects);
-	if (lseek(p->pack_fd, p->pack_size - sizeof(sha1), SEEK_SET) == -1)
+	if (lseek(p->pack_fd, p->pack_size - hashsz, SEEK_SET) == -1)
 		return error("end of packfile %s is unavailable", p->pack_name);
-	read_result = read_in_full(p->pack_fd, sha1, sizeof(sha1));
+	read_result = read_in_full(p->pack_fd, hash, hashsz);
 	if (read_result < 0)
 		return error_errno("error reading from %s", p->pack_name);
-	if (read_result != sizeof(sha1))
+	if (read_result != hashsz)
 		return error("packfile %s signature is unavailable", p->pack_name);
-	idx_sha1 = ((unsigned char *)p->index_data) + p->index_size - 40;
-	if (hashcmp(sha1, idx_sha1))
+	idx_hash = ((unsigned char *)p->index_data) + p->index_size - hashsz * 2;
+	if (hashcmp(hash, idx_hash))
 		return error("packfile %s does not match index", p->pack_name);
 	return 0;
 }
@ -530,7 +532,7 @@ static int open_packed_git(struct packed_git *p)

 static int in_window(struct pack_window *win, off_t offset)
 {
-	/* We must promise at least 20 bytes (one hash) after the
+	/* We must promise at least one full hash after the
 	 * offset is available from this window, otherwise the offset
 	 * is not actually in this window and a different window (which
 	 * has that one hash excess) must be used.  This is to support
@ -538,7 +540,7 @@ static int in_window(struct pack_window *win, off_t offset)
 	 */
 	off_t win_off = win->offset;
 	return win_off <= offset
-		&& (offset + 20) <= (win_off + win->len);
+		&& (offset + the_hash_algo->rawsz) <= (win_off + win->len);
 }

 unsigned char *use_pack(struct packed_git *p,
@ -555,7 +557,7 @@ unsigned char *use_pack(struct packed_git *p,
 	 */
 	if (!p->pack_size && p->pack_fd == -1 && open_packed_git(p))
 		die("packfile %s cannot be accessed", p->pack_name);
-	if (offset > (p->pack_size - 20))
+	if (offset > (p->pack_size - the_hash_algo->rawsz))
 		die("offset beyond end of packfile (truncated pack?)");
 	if (offset < 0)
 		die(_("offset before end of packfile (broken .idx?)"));
@ -675,7 +677,8 @@ struct packed_git *add_packed_git(const char *path, size_t path_len, int local)
 	p->pack_size = st.st_size;
 	p->pack_local = local;
 	p->mtime = st.st_mtime;
-	if (path_len < 40 || get_sha1_hex(path + path_len - 40, p->sha1))
+	if (path_len < the_hash_algo->hexsz ||
+	    get_sha1_hex(path + path_len - the_hash_algo->hexsz, p->sha1))
 		hashclr(p->sha1);
 	return p;
 }
@ -1028,7 +1031,8 @@ const struct packed_git *has_packed_and_bad(const unsigned char *sha1)

 	for (p = the_repository->objects->packed_git; p; p = p->next)
 		for (i = 0; i < p->num_bad_objects; i++)
-			if (!hashcmp(sha1, p->bad_object_sha1 + 20 * i))
+			if (!hashcmp(sha1,
+				     p->bad_object_sha1 + the_hash_algo->rawsz * i))
 				return p;
 	return NULL;
 }
@ -1066,7 +1070,7 @@ static off_t get_delta_base(struct packed_git *p,
 	} else if (type == OBJ_REF_DELTA) {
 		/* The base entry _must_ be in the same pack */
 		base_offset = find_pack_entry_one(base_info, p);
-		*curpos += 20;
+		*curpos += the_hash_algo->rawsz;
 	} else
 		die("I am totally screwed");
 	return base_offset;
@ -1677,6 +1681,7 @@ int bsearch_pack(const struct object_id *oid, const struct packed_git *p, uint32
 {
 	const unsigned char *index_fanout = p->index_data;
 	const unsigned char *index_lookup;
+	const unsigned int hashsz = the_hash_algo->rawsz;
 	int index_lookup_width;

 	if (!index_fanout)
@ -1684,10 +1689,10 @@ int bsearch_pack(const struct object_id *oid, const struct packed_git *p, uint32

 	index_lookup = index_fanout + 4 * 256;
 	if (p->index_version == 1) {
-		index_lookup_width = 24;
+		index_lookup_width = hashsz + 4;
 		index_lookup += 4;
 	} else {
-		index_lookup_width = 20;
+		index_lookup_width = hashsz;
 		index_fanout += 8;
 		index_lookup += 8;
 	}
@ -1700,6 +1705,7 @@ const unsigned char *nth_packed_object_sha1(struct packed_git *p,
 					    uint32_t n)
 {
 	const unsigned char *index = p->index_data;
+	const unsigned int hashsz = the_hash_algo->rawsz;
 	if (!index) {
 		if (open_pack_index(p))
 			return NULL;
@ -1709,10 +1715,10 @@ const unsigned char *nth_packed_object_sha1(struct packed_git *p,
 		return NULL;
 	index += 4 * 256;
 	if (p->index_version == 1) {
-		return index + 24 * n + 4;
+		return index + (hashsz + 4) * n + 4;
 	} else {
 		index += 8;
-		return index + 20 * n;
+		return index + hashsz * n;
 	}
 }

@ -1744,12 +1750,13 @@ void check_pack_index_ptr(const struct packed_git *p, const void *vptr)
 off_t nth_packed_object_offset(const struct packed_git *p, uint32_t n)
 {
 	const unsigned char *index = p->index_data;
+	const unsigned int hashsz = the_hash_algo->rawsz;
 	index += 4 * 256;
 	if (p->index_version == 1) {
-		return ntohl(*((uint32_t *)(index + 24 * n)));
+		return ntohl(*((uint32_t *)(index + (hashsz + 4) * n)));
 	} else {
 		uint32_t off;
-		index += 8 + p->num_objects * (20 + 4);
+		index += 8 + p->num_objects * (hashsz + 4);
 		off = ntohl(*((uint32_t *)(index + 4 * n)));
 		if (!(off & 0x80000000))
 			return off;
@ -1811,7 +1818,7 @@ struct packed_git *find_sha1_pack(const unsigned char *sha1,

 }

-static int fill_pack_entry(const unsigned char *sha1,
+static int fill_pack_entry(const struct object_id *oid,
 			   struct pack_entry *e,
 			   struct packed_git *p)
 {
@ -1820,11 +1827,12 @@ static int fill_pack_entry(const unsigned char *sha1,
 	if (p->num_bad_objects) {
 		unsigned i;
 		for (i = 0; i < p->num_bad_objects; i++)
-			if (!hashcmp(sha1, p->bad_object_sha1 + 20 * i))
+			if (!hashcmp(oid->hash,
+				     p->bad_object_sha1 + the_hash_algo->rawsz * i))
 				return 0;
 	}

-	offset = find_pack_entry_one(sha1, p);
+	offset = find_pack_entry_one(oid->hash, p);
 	if (!offset)
 		return 0;

@ -1839,11 +1847,10 @@ static int fill_pack_entry(const unsigned char *sha1,
 		return 0;
 	e->offset = offset;
 	e->p = p;
-	hashcpy(e->sha1, sha1);
 	return 1;
 }

-int find_pack_entry(struct repository *r, const unsigned char *sha1, struct pack_entry *e)
+int find_pack_entry(struct repository *r, const struct object_id *oid, struct pack_entry *e)
 {
 	struct list_head *pos;

@ -1853,7 +1860,7 @@ int find_pack_entry(struct repository *r, const unsigned char *sha1, struct pack

 	list_for_each(pos, &r->objects->packed_git_mru) {
 		struct packed_git *p = list_entry(pos, struct packed_git, mru);
-		if (fill_pack_entry(sha1, e, p)) {
+		if (fill_pack_entry(oid, e, p)) {
 			list_move(&p->mru, &r->objects->packed_git_mru);
 			return 1;
 		}
@ -1861,10 +1868,10 @@ int find_pack_entry(struct repository *r, const unsigned char *sha1, struct pack
 	return 0;
 }

-int has_sha1_pack(const unsigned char *sha1)
+int has_object_pack(const struct object_id *oid)
 {
 	struct pack_entry e;
-	return find_pack_entry(the_repository, sha1, &e);
+	return find_pack_entry(the_repository, oid, &e);
 }

 int has_pack_index(const unsigned char *sha1)
--- a/packfile.h
+++ b/packfile.h
@ -137,9 +137,9 @@ extern const struct packed_git *has_packed_and_bad(const unsigned char *sha1);
 * Iff a pack file in the given repository contains the object named by sha1,
 * return true and store its location to e.
 */
-extern int find_pack_entry(struct repository *r, const unsigned char *sha1, struct pack_entry *e);
+extern int find_pack_entry(struct repository *r, const struct object_id *oid, struct pack_entry *e);

-extern int has_sha1_pack(const unsigned char *sha1);
+extern int has_object_pack(const struct object_id *oid);

 extern int has_pack_index(const unsigned char *sha1);

--- a/read-cache.c
+++ b/read-cache.c
@ -1831,7 +1831,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	if (verify_hdr(hdr, mmap_size) < 0)
 		goto unmap;

-	hashcpy(istate->sha1, (const unsigned char *)hdr + mmap_size - the_hash_algo->rawsz);
+	hashcpy(istate->oid.hash, (const unsigned char *)hdr + mmap_size - the_hash_algo->rawsz);
 	istate->version = ntohl(hdr->hdr_version);
 	istate->cache_nr = ntohl(hdr->hdr_entries);
 	istate->cache_alloc = alloc_nr(istate->cache_nr);
@ -1903,7 +1903,7 @@ int read_index_from(struct index_state *istate, const char *path,
 	uint64_t start = getnanotime();
 	struct split_index *split_index;
 	int ret;
-	char *base_sha1_hex;
+	char *base_oid_hex;
 	char *base_path;

 	/* istate->initialized covers both .git/index and .git/sharedindex.xxx */
@ -1914,7 +1914,7 @@ int read_index_from(struct index_state *istate, const char *path,
 	trace_performance_since(start, "read cache %s", path);

 	split_index = istate->split_index;
-	if (!split_index || is_null_sha1(split_index->base_sha1)) {
+	if (!split_index || is_null_oid(&split_index->base_oid)) {
 		post_read_index_from(istate);
 		return ret;
 	}
@ -1924,13 +1924,13 @@ int read_index_from(struct index_state *istate, const char *path,
 	else
 		split_index->base = xcalloc(1, sizeof(*split_index->base));

-	base_sha1_hex = sha1_to_hex(split_index->base_sha1);
-	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_sha1_hex);
+	base_oid_hex = oid_to_hex(&split_index->base_oid);
+	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_oid_hex);
 	ret = do_read_index(split_index->base, base_path, 1);
-	if (hashcmp(split_index->base_sha1, split_index->base->sha1))
+	if (oidcmp(&split_index->base_oid, &split_index->base->oid))
 		die("broken index, expect %s in %s, got %s",
-		    base_sha1_hex, base_path,
-		    sha1_to_hex(split_index->base->sha1));
+		    base_oid_hex, base_path,
+		    oid_to_hex(&split_index->base->oid));

 	freshen_shared_index(base_path, 0);
 	merge_base_index(istate);
@ -2219,7 +2219,7 @@ static int verify_index_from(const struct index_state *istate, const char *path)
 	if (n != the_hash_algo->rawsz)
 		goto out;

-	if (hashcmp(istate->sha1, hash))
+	if (hashcmp(istate->oid.hash, hash))
 		goto out;

 	close(fd);
@ -2398,7 +2398,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 			return -1;
 	}

-	if (ce_flush(&c, newfd, istate->sha1))
+	if (ce_flush(&c, newfd, istate->oid.hash))
 		return -1;
 	if (close_tempfile_gently(tempfile)) {
 		error(_("could not close '%s'"), tempfile->filename.buf);
@ -2522,10 +2522,10 @@ static int write_shared_index(struct index_state *istate,
 		return ret;
 	}
 	ret = rename_tempfile(temp,
-			      git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
+			      git_path("sharedindex.%s", oid_to_hex(&si->base->oid)));
 	if (!ret) {
-		hashcpy(si->base_sha1, si->base->sha1);
-		clean_shared_index_files(sha1_to_hex(si->base->sha1));
+		oidcpy(&si->base_oid, &si->base->oid);
+		clean_shared_index_files(oid_to_hex(&si->base->oid));
 	}

 	return ret;
@ -2579,13 +2579,13 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 	if (!si || alternate_index_output ||
 	    (istate->cache_changed & ~EXTMASK)) {
 		if (si)
-			hashclr(si->base_sha1);
+			oidclr(&si->base_oid);
 		ret = do_write_locked_index(istate, lock, flags);
 		goto out;
 	}

 	if (git_env_bool("GIT_TEST_SPLIT_INDEX", 0)) {
-		int v = si->base_sha1[0];
+		int v = si->base_oid.hash[0];
 		if ((v & 15) < 6)
 			istate->cache_changed |= SPLIT_INDEX_ORDERED;
 	}
@ -2600,7 +2600,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,

 		temp = mks_tempfile(git_path("sharedindex_XXXXXX"));
 		if (!temp) {
-			hashclr(si->base_sha1);
+			oidclr(&si->base_oid);
 			ret = do_write_locked_index(istate, lock, flags);
 			goto out;
 		}
@ -2620,7 +2620,7 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 	/* Freshen the shared index only if the split-index was written */
 	if (!ret && !new_shared_index) {
 		const char *shared_index = git_path("sharedindex.%s",
-						    sha1_to_hex(si->base_sha1));
+						    oid_to_hex(&si->base_oid));
 		freshen_shared_index(shared_index, 1);
 	}

--- a/resolve-undo.c
+++ b/resolve-undo.c
@ -90,7 +90,7 @@ struct string_list *resolve_undo_read(const char *data, unsigned long size)
 				continue;
 			if (size < rawsz)
 				goto error;
-			memcpy(ui->oid[i].hash, (const unsigned char *)data, rawsz);
+			oidread(&ui->oid[i], (const unsigned char *)data);
 			size -= rawsz;
 			data += rawsz;
 		}
--- a/revision.c
+++ b/revision.c
@ -1762,6 +1762,7 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	const char *arg = argv[0];
 	const char *optarg;
 	int argcount;
+	const unsigned hexsz = the_hash_algo->hexsz;

 	/* pseudo revision arguments */
 	if (!strcmp(arg, "--all") || !strcmp(arg, "--branches") ||
@ -2049,8 +2050,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->abbrev = strtoul(optarg, NULL, 10);
 		if (revs->abbrev < MINIMUM_ABBREV)
 			revs->abbrev = MINIMUM_ABBREV;
-		else if (revs->abbrev > 40)
-			revs->abbrev = 40;
+		else if (revs->abbrev > hexsz)
+			revs->abbrev = hexsz;
 	} else if (!strcmp(arg, "--abbrev-commit")) {
 		revs->abbrev_commit = 1;
 		revs->abbrev_commit_given = 1;
@ -3097,7 +3098,7 @@ enum commit_action get_commit_action(struct rev_info *revs, struct commit *commi
 {
 	if (commit->object.flags & SHOWN)
 		return commit_ignore;
-	if (revs->unpacked && has_sha1_pack(commit->object.oid.hash))
+	if (revs->unpacked && has_object_pack(&commit->object.oid))
 		return commit_ignore;
 	if (commit->object.flags & UNINTERESTING)
 		return commit_ignore;
--- a/sequencer.c
+++ b/sequencer.c
@ -1247,7 +1247,7 @@ static int try_to_commit(struct strbuf *msg, const char *author,

 	if (!(flags & ALLOW_EMPTY) && !oidcmp(current_head ?
 					      get_commit_tree_oid(current_head) :
-					      &empty_tree_oid, &tree)) {
+					      the_hash_algo->empty_tree, &tree)) {
 		res = 1; /* run 'git commit' to display error message */
 		goto out;
 	}
@ -1639,7 +1639,7 @@ static int do_pick_commit(enum todo_command command, struct commit *commit,
 			unborn = 1;
 		} else if (unborn)
 			oidcpy(&head, the_hash_algo->empty_tree);
-		if (index_differs_from(unborn ? EMPTY_TREE_SHA1_HEX : "HEAD",
+		if (index_differs_from(unborn ? empty_tree_oid_hex() : "HEAD",
 				       NULL, 0))
 			return error_dirty_index(opts);
 	}
--- a/server-info.c
+++ b/server-info.c
@ -92,8 +92,6 @@ static struct pack_info {
 	int old_num;
 	int new_num;
 	int nr_alloc;
-	int nr_heads;
-	unsigned char (*head)[20];
 } **info;
 static int num_pack;
 static const char *objdir;
@ -225,12 +223,9 @@ static void init_pack_info(const char *infofile, int force)
 	else
 		stale = 1;

-	for (i = 0; i < num_pack; i++) {
-		if (stale) {
+	for (i = 0; i < num_pack; i++)
+		if (stale)
 			info[i]->old_num = -1;
-			info[i]->nr_heads = 0;
-		}
-	}

 	/* renumber them */
 	QSORT(info, num_pack, compare_info);
--- a/sha1-file.c
+++ b/sha1-file.c
@ -36,12 +36,21 @@
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32

+
+#define EMPTY_TREE_SHA1_BIN_LITERAL \
+	 "\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60" \
+	 "\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04"
+
+#define EMPTY_BLOB_SHA1_BIN_LITERAL \
+	"\xe6\x9d\xe2\x9b\xb2\xd1\xd6\x43\x4b\x8b" \
+	"\x29\xae\x77\x5a\xd8\xc2\xe4\x8c\x53\x91"
+
 const unsigned char null_sha1[GIT_MAX_RAWSZ];
 const struct object_id null_oid;
-const struct object_id empty_tree_oid = {
+static const struct object_id empty_tree_oid = {
 	EMPTY_TREE_SHA1_BIN_LITERAL
 };
-const struct object_id empty_blob_oid = {
+static const struct object_id empty_blob_oid = {
 	EMPTY_BLOB_SHA1_BIN_LITERAL
 };

@ -101,6 +110,18 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 	},
 };

+const char *empty_tree_oid_hex(void)
+{
+	static char buf[GIT_MAX_HEXSZ + 1];
+	return oid_to_hex_r(buf, the_hash_algo->empty_tree);
+}
+
+const char *empty_blob_oid_hex(void)
+{
+	static char buf[GIT_MAX_HEXSZ + 1];
+	return oid_to_hex_r(buf, the_hash_algo->empty_blob);
+}
+
 /*
 * This is meant to hold a *small* number of objects that you would
 * want read_sha1_file() to be able to return, but yet you do not want
@ -108,7 +129,7 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
 * application).
 */
 static struct cached_object {
-	unsigned char sha1[20];
+	struct object_id oid;
 	enum object_type type;
 	void *buf;
 	unsigned long size;
@ -116,22 +137,22 @@ static struct cached_object {
 static int cached_object_nr, cached_object_alloc;

 static struct cached_object empty_tree = {
-	EMPTY_TREE_SHA1_BIN_LITERAL,
+	{ EMPTY_TREE_SHA1_BIN_LITERAL },
 	OBJ_TREE,
 	"",
 	0
 };

-static struct cached_object *find_cached_object(const unsigned char *sha1)
+static struct cached_object *find_cached_object(const struct object_id *oid)
 {
 	int i;
 	struct cached_object *co = cached_objects;

 	for (i = 0; i < cached_object_nr; i++, co++) {
-		if (!hashcmp(co->sha1, sha1))
+		if (!oidcmp(&co->oid, oid))
 			return co;
 	}
-	if (!hashcmp(sha1, empty_tree.sha1))
+	if (!oidcmp(oid, the_hash_algo->empty_tree))
 		return &empty_tree;
 	return NULL;
 }
@ -710,42 +731,42 @@ int check_and_freshen_file(const char *fn, int freshen)
 	return 1;
 }

-static int check_and_freshen_local(const unsigned char *sha1, int freshen)
+static int check_and_freshen_local(const struct object_id *oid, int freshen)
 {
 	static struct strbuf buf = STRBUF_INIT;

 	strbuf_reset(&buf);
-	sha1_file_name(the_repository, &buf, sha1);
+	sha1_file_name(the_repository, &buf, oid->hash);

 	return check_and_freshen_file(buf.buf, freshen);
 }

-static int check_and_freshen_nonlocal(const unsigned char *sha1, int freshen)
+static int check_and_freshen_nonlocal(const struct object_id *oid, int freshen)
 {
 	struct alternate_object_database *alt;
 	prepare_alt_odb(the_repository);
 	for (alt = the_repository->objects->alt_odb_list; alt; alt = alt->next) {
-		const char *path = alt_sha1_path(alt, sha1);
+		const char *path = alt_sha1_path(alt, oid->hash);
 		if (check_and_freshen_file(path, freshen))
 			return 1;
 	}
 	return 0;
 }

-static int check_and_freshen(const unsigned char *sha1, int freshen)
+static int check_and_freshen(const struct object_id *oid, int freshen)
 {
-	return check_and_freshen_local(sha1, freshen) ||
-	       check_and_freshen_nonlocal(sha1, freshen);
+	return check_and_freshen_local(oid, freshen) ||
+	       check_and_freshen_nonlocal(oid, freshen);
 }

-int has_loose_object_nonlocal(const unsigned char *sha1)
+int has_loose_object_nonlocal(const struct object_id *oid)
 {
-	return check_and_freshen_nonlocal(sha1, 0);
+	return check_and_freshen_nonlocal(oid, 0);
 }

-static int has_loose_object(const unsigned char *sha1)
+static int has_loose_object(const struct object_id *oid)
 {
-	return check_and_freshen(sha1, 0);
+	return check_and_freshen(oid, 0);
 }

 static void mmap_limit_check(size_t length)
@ -1250,7 +1271,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 		oi = &blank_oi;

 	if (!(flags & OBJECT_INFO_SKIP_CACHED)) {
-		struct cached_object *co = find_cached_object(real->hash);
+		struct cached_object *co = find_cached_object(real);
 		if (co) {
 			if (oi->typep)
 				*(oi->typep) = co->type;
@ -1270,7 +1291,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 	}

 	while (1) {
-		if (find_pack_entry(r, real->hash, &e))
+		if (find_pack_entry(r, real, &e))
 			break;

 		if (flags & OBJECT_INFO_IGNORE_LOOSE)
@ -1283,7 +1304,7 @@ int oid_object_info_extended(struct repository *r, const struct object_id *oid,
 		/* Not a loose object; someone else may have just packed it. */
 		if (!(flags & OBJECT_INFO_QUICK)) {
 			reprepare_packed_git(r);
-			if (find_pack_entry(r, real->hash, &e))
+			if (find_pack_entry(r, real, &e))
 				break;
 		}

@ -1363,7 +1384,7 @@ int pretend_object_file(void *buf, unsigned long len, enum object_type type,
 	struct cached_object *co;

 	hash_object_file(buf, len, type_name(type), oid);
-	if (has_sha1_file(oid->hash) || find_cached_object(oid->hash))
+	if (has_sha1_file(oid->hash) || find_cached_object(oid))
 		return 0;
 	ALLOC_GROW(cached_objects, cached_object_nr + 1, cached_object_alloc);
 	co = &cached_objects[cached_object_nr++];
@ -1371,7 +1392,7 @@ int pretend_object_file(void *buf, unsigned long len, enum object_type type,
 	co->type = type;
 	co->buf = xmalloc(len);
 	memcpy(co->buf, buf, len);
-	hashcpy(co->sha1, oid->hash);
+	oidcpy(&co->oid, oid);
 	return 0;
 }

@ -1667,15 +1688,15 @@ static int write_loose_object(const struct object_id *oid, char *hdr,
 	return finalize_object_file(tmp_file.buf, filename.buf);
 }

-static int freshen_loose_object(const unsigned char *sha1)
+static int freshen_loose_object(const struct object_id *oid)
 {
-	return check_and_freshen(sha1, 1);
+	return check_and_freshen(oid, 1);
 }

-static int freshen_packed_object(const unsigned char *sha1)
+static int freshen_packed_object(const struct object_id *oid)
 {
 	struct pack_entry e;
-	if (!find_pack_entry(the_repository, sha1, &e))
+	if (!find_pack_entry(the_repository, oid, &e))
 		return 0;
 	if (e.p->freshened)
 		return 1;
@ -1695,7 +1716,7 @@ int write_object_file(const void *buf, unsigned long len, const char *type,
 	 * it out into .git/objects/??/?{38} file.
 	 */
 	write_object_file_prepare(buf, len, type, oid, hdr, &hdrlen);
-	if (freshen_packed_object(oid->hash) || freshen_loose_object(oid->hash))
+	if (freshen_packed_object(oid) || freshen_loose_object(oid))
 		return 0;
 	return write_loose_object(oid, hdr, hdrlen, buf, len, 0);
 }
@ -1714,7 +1735,7 @@ int hash_object_file_literally(const void *buf, unsigned long len,

 	if (!(flags & HASH_WRITE_OBJECT))
 		goto cleanup;
-	if (freshen_packed_object(oid->hash) || freshen_loose_object(oid->hash))
+	if (freshen_packed_object(oid) || freshen_loose_object(oid))
 		goto cleanup;
 	status = write_loose_object(oid, header, hdrlen, buf, len, 0);

@ -1732,7 +1753,7 @@ int force_object_loose(const struct object_id *oid, time_t mtime)
 	int hdrlen;
 	int ret;

-	if (has_loose_object(oid->hash))
+	if (has_loose_object(oid))
 		return 0;
 	buf = read_object(oid->hash, &type, &len);
 	if (!buf)
--- a/sha1-name.c
+++ b/sha1-name.c
@ -1685,8 +1685,8 @@ static int get_oid_with_context_1(const char *name,
 			if (new_filename)
 				filename = new_filename;
 			if (flags & GET_OID_FOLLOW_SYMLINKS) {
-				ret = get_tree_entry_follow_symlinks(tree_oid.hash,
-					filename, oid->hash, &oc->symlink_path,
+				ret = get_tree_entry_follow_symlinks(&tree_oid,
+					filename, oid, &oc->symlink_path,
 					&oc->mode);
 			} else {
 				ret = get_tree_entry(&tree_oid, filename, oid,
@ -1698,7 +1698,6 @@ static int get_oid_with_context_1(const char *name,
 								   name, len);
 				}
 			}
-			hashcpy(oc->tree, tree_oid.hash);
 			if (flags & GET_OID_RECORD_PATH)
 				oc->path = xstrdup(filename);

--- a/split-index.c
+++ b/split-index.c
@ -18,12 +18,12 @@ int read_link_extension(struct index_state *istate,
 	struct split_index *si;
 	int ret;

-	if (sz < 20)
+	if (sz < the_hash_algo->rawsz)
 		return error("corrupt link extension (too short)");
 	si = init_split_index(istate);
-	hashcpy(si->base_sha1, data);
-	data += 20;
-	sz -= 20;
+	hashcpy(si->base_oid.hash, data);
+	data += the_hash_algo->rawsz;
+	sz -= the_hash_algo->rawsz;
 	if (!sz)
 		return 0;
 	si->delete_bitmap = ewah_new();
@ -45,7 +45,7 @@ int write_link_extension(struct strbuf *sb,
 			 struct index_state *istate)
 {
 	struct split_index *si = istate->split_index;
-	strbuf_add(sb, si->base_sha1, 20);
+	strbuf_add(sb, si->base_oid.hash, the_hash_algo->rawsz);
 	if (!si->delete_bitmap && !si->replace_bitmap)
 		return 0;
 	ewah_serialize_strbuf(si->delete_bitmap, sb);
--- a/split-index.h
+++ b/split-index.h
@ -1,12 +1,14 @@
 #ifndef SPLIT_INDEX_H
 #define SPLIT_INDEX_H

+#include "cache.h"
+
 struct index_state;
 struct strbuf;
 struct ewah_bitmap;

 struct split_index {
-	unsigned char base_sha1[20];
+	struct object_id base_oid;
 	struct index_state *base;
 	struct ewah_bitmap *delete_bitmap;
 	struct ewah_bitmap *replace_bitmap;
--- a/submodule-config.c
+++ b/submodule-config.c
@ -44,7 +44,7 @@ static int config_path_cmp(const void *unused_cmp_data,
 	const struct submodule_entry *b = entry_or_key;

 	return strcmp(a->config->path, b->config->path) ||
-	       hashcmp(a->config->gitmodules_sha1, b->config->gitmodules_sha1);
+	       oidcmp(&a->config->gitmodules_oid, &b->config->gitmodules_oid);
 }

 static int config_name_cmp(const void *unused_cmp_data,
@ -56,7 +56,7 @@ static int config_name_cmp(const void *unused_cmp_data,
 	const struct submodule_entry *b = entry_or_key;

 	return strcmp(a->config->name, b->config->name) ||
-	       hashcmp(a->config->gitmodules_sha1, b->config->gitmodules_sha1);
+	       oidcmp(&a->config->gitmodules_oid, &b->config->gitmodules_oid);
 }

 static struct submodule_cache *submodule_cache_alloc(void)
@ -109,17 +109,17 @@ void submodule_cache_free(struct submodule_cache *cache)
 	free(cache);
 }

-static unsigned int hash_sha1_string(const unsigned char *sha1,
-				     const char *string)
+static unsigned int hash_oid_string(const struct object_id *oid,
+				    const char *string)
 {
-	return memhash(sha1, 20) + strhash(string);
+	return memhash(oid->hash, the_hash_algo->rawsz) + strhash(string);
 }

 static void cache_put_path(struct submodule_cache *cache,
 			   struct submodule *submodule)
 {
-	unsigned int hash = hash_sha1_string(submodule->gitmodules_sha1,
-					     submodule->path);
+	unsigned int hash = hash_oid_string(&submodule->gitmodules_oid,
+					    submodule->path);
 	struct submodule_entry *e = xmalloc(sizeof(*e));
 	hashmap_entry_init(e, hash);
 	e->config = submodule;
@ -129,8 +129,8 @@ static void cache_put_path(struct submodule_cache *cache,
 static void cache_remove_path(struct submodule_cache *cache,
 			      struct submodule *submodule)
 {
-	unsigned int hash = hash_sha1_string(submodule->gitmodules_sha1,
-					     submodule->path);
+	unsigned int hash = hash_oid_string(&submodule->gitmodules_oid,
+					    submodule->path);
 	struct submodule_entry e;
 	struct submodule_entry *removed;
 	hashmap_entry_init(&e, hash);
@ -142,8 +142,8 @@ static void cache_remove_path(struct submodule_cache *cache,
 static void cache_add(struct submodule_cache *cache,
 		      struct submodule *submodule)
 {
-	unsigned int hash = hash_sha1_string(submodule->gitmodules_sha1,
-					     submodule->name);
+	unsigned int hash = hash_oid_string(&submodule->gitmodules_oid,
+					    submodule->name);
 	struct submodule_entry *e = xmalloc(sizeof(*e));
 	hashmap_entry_init(e, hash);
 	e->config = submodule;
@ -151,14 +151,14 @@ static void cache_add(struct submodule_cache *cache,
 }

 static const struct submodule *cache_lookup_path(struct submodule_cache *cache,
-		const unsigned char *gitmodules_sha1, const char *path)
+		const struct object_id *gitmodules_oid, const char *path)
 {
 	struct submodule_entry *entry;
-	unsigned int hash = hash_sha1_string(gitmodules_sha1, path);
+	unsigned int hash = hash_oid_string(gitmodules_oid, path);
 	struct submodule_entry key;
 	struct submodule key_config;

-	hashcpy(key_config.gitmodules_sha1, gitmodules_sha1);
+	oidcpy(&key_config.gitmodules_oid, gitmodules_oid);
 	key_config.path = path;

 	hashmap_entry_init(&key, hash);
@ -171,14 +171,14 @@ static const struct submodule *cache_lookup_path(struct submodule_cache *cache,
 }

 static struct submodule *cache_lookup_name(struct submodule_cache *cache,
-		const unsigned char *gitmodules_sha1, const char *name)
+		const struct object_id *gitmodules_oid, const char *name)
 {
 	struct submodule_entry *entry;
-	unsigned int hash = hash_sha1_string(gitmodules_sha1, name);
+	unsigned int hash = hash_oid_string(gitmodules_oid, name);
 	struct submodule_entry key;
 	struct submodule key_config;

-	hashcpy(key_config.gitmodules_sha1, gitmodules_sha1);
+	oidcpy(&key_config.gitmodules_oid, gitmodules_oid);
 	key_config.name = name;

 	hashmap_entry_init(&key, hash);
@ -238,12 +238,12 @@ static int name_and_item_from_var(const char *var, struct strbuf *name,
 }

 static struct submodule *lookup_or_create_by_name(struct submodule_cache *cache,
-		const unsigned char *gitmodules_sha1, const char *name)
+		const struct object_id *gitmodules_oid, const char *name)
 {
 	struct submodule *submodule;
 	struct strbuf name_buf = STRBUF_INIT;

-	submodule = cache_lookup_name(cache, gitmodules_sha1, name);
+	submodule = cache_lookup_name(cache, gitmodules_oid, name);
 	if (submodule)
 		return submodule;

@ -261,7 +261,7 @@ static struct submodule *lookup_or_create_by_name(struct submodule_cache *cache,
 	submodule->branch = NULL;
 	submodule->recommend_shallow = -1;

-	hashcpy(submodule->gitmodules_sha1, gitmodules_sha1);
+	oidcpy(&submodule->gitmodules_oid, gitmodules_oid);

 	cache_add(cache, submodule);

@ -372,12 +372,12 @@ int parse_push_recurse_submodules_arg(const char *opt, const char *arg)
 	return parse_push_recurse(opt, arg, 1);
 }

-static void warn_multiple_config(const unsigned char *treeish_name,
+static void warn_multiple_config(const struct object_id *treeish_name,
 				 const char *name, const char *option)
 {
 	const char *commit_string = "WORKTREE";
 	if (treeish_name)
-		commit_string = sha1_to_hex(treeish_name);
+		commit_string = oid_to_hex(treeish_name);
 	warning("%s:.gitmodules, multiple configurations found for "
 			"'submodule.%s.%s'. Skipping second one!",
 			commit_string, name, option);
@ -385,8 +385,8 @@ static void warn_multiple_config(const unsigned char *treeish_name,

 struct parse_config_parameter {
 	struct submodule_cache *cache;
-	const unsigned char *treeish_name;
-	const unsigned char *gitmodules_sha1;
+	const struct object_id *treeish_name;
+	const struct object_id *gitmodules_oid;
 	int overwrite;
 };

@ -402,7 +402,7 @@ static int parse_config(const char *var, const char *value, void *data)
 		return 0;

 	submodule = lookup_or_create_by_name(me->cache,
-					     me->gitmodules_sha1,
+					     me->gitmodules_oid,
 					     name.buf);

 	if (!strcmp(item.buf, "path")) {
@ -420,7 +420,7 @@ static int parse_config(const char *var, const char *value, void *data)
 		}
 	} else if (!strcmp(item.buf, "fetchrecursesubmodules")) {
 		/* when parsing worktree configurations we can die early */
-		int die_on_error = is_null_sha1(me->gitmodules_sha1);
+		int die_on_error = is_null_oid(me->gitmodules_oid);
 		if (!me->overwrite &&
 		    submodule->fetch_recurse != RECURSE_SUBMODULES_NONE)
 			warn_multiple_config(me->treeish_name, submodule->name,
@ -542,10 +542,10 @@ static const struct submodule *config_from(struct submodule_cache *cache,

 	switch (lookup_type) {
 	case lookup_name:
-		submodule = cache_lookup_name(cache, oid.hash, key);
+		submodule = cache_lookup_name(cache, &oid, key);
 		break;
 	case lookup_path:
-		submodule = cache_lookup_path(cache, oid.hash, key);
+		submodule = cache_lookup_path(cache, &oid, key);
 		break;
 	}
 	if (submodule)
@ -557,8 +557,8 @@ static const struct submodule *config_from(struct submodule_cache *cache,

 	/* fill the submodule config into the cache */
 	parameter.cache = cache;
-	parameter.treeish_name = treeish_name->hash;
-	parameter.gitmodules_sha1 = oid.hash;
+	parameter.treeish_name = treeish_name;
+	parameter.gitmodules_oid = &oid;
 	parameter.overwrite = 0;
 	git_config_from_mem(parse_config, CONFIG_ORIGIN_SUBMODULE_BLOB, rev.buf,
 			config, config_size, &parameter);
@ -567,9 +567,9 @@ static const struct submodule *config_from(struct submodule_cache *cache,

 	switch (lookup_type) {
 	case lookup_name:
-		return cache_lookup_name(cache, oid.hash, key);
+		return cache_lookup_name(cache, &oid, key);
 	case lookup_path:
-		return cache_lookup_path(cache, oid.hash, key);
+		return cache_lookup_path(cache, &oid, key);
 	default:
 		return NULL;
 	}
@ -598,7 +598,7 @@ static int gitmodules_cb(const char *var, const char *value, void *data)

 	parameter.cache = repo->submodule_cache;
 	parameter.treeish_name = NULL;
-	parameter.gitmodules_sha1 = null_sha1;
+	parameter.gitmodules_oid = &null_oid;
 	parameter.overwrite = 1;

 	return parse_config(var, value, &parameter);
--- a/submodule-config.h
+++ b/submodule-config.h
@ -1,6 +1,7 @@
 #ifndef SUBMODULE_CONFIG_CACHE_H
 #define SUBMODULE_CONFIG_CACHE_H

+#include "cache.h"
 #include "hashmap.h"
 #include "submodule.h"
 #include "strbuf.h"
@ -17,13 +18,13 @@ struct submodule {
 	const char *ignore;
 	const char *branch;
 	struct submodule_update_strategy update_strategy;
-	/* the sha1 blob id of the responsible .gitmodules file */
-	unsigned char gitmodules_sha1[20];
+	/* the object id of the responsible .gitmodules file */
+	struct object_id gitmodules_oid;
 	int recommend_shallow;
 };

 #define SUBMODULE_INIT { NULL, NULL, NULL, RECURSE_SUBMODULES_NONE, \
-	NULL, NULL, SUBMODULE_UPDATE_STRATEGY_INIT, {0}, -1 };
+	NULL, NULL, SUBMODULE_UPDATE_STRATEGY_INIT, { { 0 } }, -1 };

 struct submodule_cache;
 struct repository;
--- a/submodule.c
+++ b/submodule.c
@ -1569,7 +1569,7 @@ static void submodule_reset_index(const char *path)
 				   get_super_prefix_or_empty(), path);
 	argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);

-	argv_array_push(&cp.args, EMPTY_TREE_SHA1_HEX);
+	argv_array_push(&cp.args, empty_tree_oid_hex());

 	if (run_command(&cp))
 		die("could not reset submodule index");
@ -1661,9 +1661,9 @@ int submodule_move_head(const char *path,
 		argv_array_push(&cp.args, "-m");

 	if (!(flags & SUBMODULE_MOVE_HEAD_FORCE))
-		argv_array_push(&cp.args, old_head ? old_head : EMPTY_TREE_SHA1_HEX);
+		argv_array_push(&cp.args, old_head ? old_head : empty_tree_oid_hex());

-	argv_array_push(&cp.args, new_head ? new_head : EMPTY_TREE_SHA1_HEX);
+	argv_array_push(&cp.args, new_head ? new_head : empty_tree_oid_hex());

 	if (run_command(&cp)) {
 		ret = -1;
--- a/t/helper/test-dump-split-index.c
+++ b/t/helper/test-dump-split-index.c
@ -14,13 +14,13 @@ int cmd__dump_split_index(int ac, const char **av)
 	int i;

 	do_read_index(&the_index, av[1], 1);
-	printf("own %s\n", sha1_to_hex(the_index.sha1));
+	printf("own %s\n", oid_to_hex(&the_index.oid));
 	si = the_index.split_index;
 	if (!si) {
 		printf("not a split index\n");
 		return 0;
 	}
-	printf("base %s\n", sha1_to_hex(si->base_sha1));
+	printf("base %s\n", oid_to_hex(&si->base_oid));
 	for (i = 0; i < the_index.cache_nr; i++) {
 		struct cache_entry *ce = the_index.cache[i];
 		printf("%06o %s %d\t%s\n", ce->ce_mode,
--- a/t/helper/test-dump-untracked-cache.c
+++ b/t/helper/test-dump-untracked-cache.c
@ -23,7 +23,7 @@ static void dump(struct untracked_cache_dir *ucd, struct strbuf *base)
 	len = base->len;
 	strbuf_addf(base, "%s/", ucd->name);
 	printf("%s %s", base->buf,
-	       sha1_to_hex(ucd->exclude_sha1));
+	       oid_to_hex(&ucd->exclude_oid));
 	if (ucd->recurse)
 		fputs(" recurse", stdout);
 	if (ucd->check_only)
--- a/templates/hooks--pre-commit.sample
+++ b/templates/hooks--pre-commit.sample
@ -12,7 +12,7 @@ then
 	against=HEAD
 else
 	# Initial commit: diff against an empty tree object
-	against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+	against=$(git hash-object -t tree /dev/null)
 fi

 # If you want to allow non-ASCII filenames set this variable to true.
--- a/tree-walk.c
+++ b/tree-walk.c
@ -105,7 +105,7 @@ static void entry_extract(struct tree_desc *t, struct name_entry *a)
 static int update_tree_entry_internal(struct tree_desc *desc, struct strbuf *err)
 {
 	const void *buf = desc->buffer;
-	const unsigned char *end = desc->entry.oid->hash + 20;
+	const unsigned char *end = desc->entry.oid->hash + the_hash_algo->rawsz;
 	unsigned long size = desc->size;
 	unsigned long len = end - (const unsigned char *)buf;

@ -488,7 +488,7 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 struct dir_state {
 	void *tree;
 	unsigned long size;
-	unsigned char sha1[20];
+	struct object_id oid;
 };

 static int find_tree_entry(struct tree_desc *t, const char *name, struct object_id *result, unsigned *mode)
@ -576,7 +576,7 @@ int get_tree_entry(const struct object_id *tree_oid, const char *name, struct ob
 * See the code for enum follow_symlink_result for a description of
 * the return values.
 */
-enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode)
+enum follow_symlinks_result get_tree_entry_follow_symlinks(struct object_id *tree_oid, const char *name, struct object_id *result, struct strbuf *result_path, unsigned *mode)
 {
 	int retval = MISSING_OBJECT;
 	struct dir_state *parents = NULL;
@ -589,7 +589,7 @@ enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_s

 	init_tree_desc(&t, NULL, 0UL);
 	strbuf_addstr(&namebuf, name);
-	hashcpy(current_tree_oid.hash, tree_sha1);
+	oidcpy(&current_tree_oid, tree_oid);

 	while (1) {
 		int find_result;
@ -609,11 +609,11 @@ enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_s
 			ALLOC_GROW(parents, parents_nr + 1, parents_alloc);
 			parents[parents_nr].tree = tree;
 			parents[parents_nr].size = size;
-			hashcpy(parents[parents_nr].sha1, root.hash);
+			oidcpy(&parents[parents_nr].oid, &root);
 			parents_nr++;

 			if (namebuf.buf[0] == '\0') {
-				hashcpy(result, root.hash);
+				oidcpy(result, &root);
 				retval = FOUND;
 				goto done;
 			}
@ -663,7 +663,7 @@ enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_s

 		/* We could end up here via a symlink to dir/.. */
 		if (namebuf.buf[0] == '\0') {
-			hashcpy(result, parents[parents_nr - 1].sha1);
+			oidcpy(result, &parents[parents_nr - 1].oid);
 			retval = FOUND;
 			goto done;
 		}
@ -677,7 +677,7 @@ enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_s

 		if (S_ISDIR(*mode)) {
 			if (!remainder) {
-				hashcpy(result, current_tree_oid.hash);
+				oidcpy(result, &current_tree_oid);
 				retval = FOUND;
 				goto done;
 			}
@ -687,7 +687,7 @@ enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_s
 				      1 + first_slash - namebuf.buf);
 		} else if (S_ISREG(*mode)) {
 			if (!remainder) {
-				hashcpy(result, current_tree_oid.hash);
+				oidcpy(result, &current_tree_oid);
 				retval = FOUND;
 			} else {
 				retval = NOT_DIR;
--- a/tree-walk.h
+++ b/tree-walk.h
@ -64,7 +64,7 @@ enum follow_symlinks_result {
 		       */
 };

-enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode);
+enum follow_symlinks_result get_tree_entry_follow_symlinks(struct object_id *tree_oid, const char *name, struct object_id *result, struct strbuf *result_path, unsigned *mode);

 struct traverse_info {
 	const char *traverse_path;
--- a/unpack-trees.c
+++ b/unpack-trees.c
@ -1298,7 +1298,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	} else {
 		o->result.split_index = init_split_index(&o->result);
 	}
-	hashcpy(o->result.sha1, o->src_index->sha1);
+	oidcpy(&o->result.oid, &o->src_index->oid);
 	o->merge_size = len;
 	mark_all_ce_unused(o->src_index);

--- a/upload-pack.c
+++ b/upload-pack.c
@ -444,7 +444,7 @@ static int get_common_commits(void)
 				break;
 			default:
 				got_common = 1;
-				memcpy(last_hex, oid_to_hex(&oid), 41);
+				oid_to_hex_r(last_hex, &oid);
 				if (multi_ack == 2)
 					packet_write_fmt(1, "ACK %s common\n", last_hex);
 				else if (multi_ack)
@ -486,7 +486,7 @@ static int do_reachable_revlist(struct child_process *cmd,
 		"rev-list", "--stdin", NULL,
 	};
 	struct object *o;
-	char namebuf[42]; /* ^ + SHA-1 + LF */
+	char namebuf[GIT_MAX_HEXSZ + 2]; /* ^ + hash + LF */
 	int i;

 	cmd->argv = argv;
@ -555,15 +555,17 @@ static int get_reachable_list(struct object_array *src,
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	int i;
 	struct object *o;
-	char namebuf[42]; /* ^ + SHA-1 + LF */
+	char namebuf[GIT_MAX_HEXSZ + 2]; /* ^ + hash + LF */
+	const unsigned hexsz = the_hash_algo->hexsz;

 	if (do_reachable_revlist(&cmd, src, reachable) < 0)
 		return -1;

-	while ((i = read_in_full(cmd.out, namebuf, 41)) == 41) {
+	while ((i = read_in_full(cmd.out, namebuf, hexsz + 1)) == hexsz + 1) {
 		struct object_id sha1;
+		const char *p;

-		if (namebuf[40] != '\n' || get_oid_hex(namebuf, &sha1))
+		if (parse_oid_hex(namebuf, &sha1, &p) || *p != '\n')
 			break;

 		o = lookup_object(sha1.hash);
@ -895,11 +897,9 @@ static void receive_needs(void)
 		}

 		if (!skip_prefix(line, "want ", &arg) ||
-		    get_oid_hex(arg, &oid_buf))
+		    parse_oid_hex(arg, &oid_buf, &features))
 			die("git upload-pack: protocol error, "
-			    "expected to get sha, not '%s'", line);
-
-		features = arg + 40;
+			    "expected to get object ID, not '%s'", line);

 		if (parse_feature_request(features, "deepen-relative"))
 			deepen_relative = 1;
--- a/wt-status.c
+++ b/wt-status.c
@ -609,7 +609,7 @@ static void wt_status_collect_changes_index(struct wt_status *s)

 	init_revisions(&rev, NULL);
 	memset(&opt, 0, sizeof(opt));
-	opt.def = s->is_initial ? EMPTY_TREE_SHA1_HEX : s->reference;
+	opt.def = s->is_initial ? empty_tree_oid_hex() : s->reference;
 	setup_revisions(0, NULL, &rev, &opt);

 	rev.diffopt.flags.override_submodule_config = 1;
@ -987,7 +987,7 @@ static void wt_longstatus_print_verbose(struct wt_status *s)
 	rev.diffopt.ita_invisible_in_index = 1;

 	memset(&opt, 0, sizeof(opt));
-	opt.def = s->is_initial ? EMPTY_TREE_SHA1_HEX : s->reference;
+	opt.def = s->is_initial ? empty_tree_oid_hex() : s->reference;
 	setup_revisions(0, NULL, &rev, &opt);

 	rev.diffopt.output_format |= DIFF_FORMAT_PATCH;