object-file: move logic to compute packed abbreviation length

Same as the preceding commit, move the logic that computes the minimum
required prefix length to make a given object ID unique for the packfile
store into a new function `packfile_store_find_abbrev_len()` that is
part of "packfile.c". This prepares for making the logic fully generic
via pluggable object databases.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 111 insertions, 0 deletions

diff --git a/packfile.c b/packfile.c
index 2539a371c1..ee9c7ea1d1 100644
--- a/packfile.c
+++ b/packfile.c
@@ -2597,6 +2597,117 @@ out:
 	return ret;
 }
 
+static int extend_abbrev_len(const struct object_id *a,
+			     const struct object_id *b,
+			     unsigned *out)
+{
+	unsigned len = oid_common_prefix_hexlen(a, b);
+	if (len != hash_algos[a->algo].hexsz && len >= *out)
+		*out = len + 1;
+	return 0;
+}
+
+static void find_abbrev_len_for_midx(struct multi_pack_index *m,
+				     const struct object_id *oid,
+				     unsigned min_len,
+				     unsigned *out)
+{
+	unsigned len = min_len;
+
+	for (; m; m = m->base_midx) {
+		int match = 0;
+		uint32_t num, first = 0;
+		struct object_id found_oid;
+
+		if (!m->num_objects)
+			continue;
+
+		num = m->num_objects + m->num_objects_in_base;
+		match = bsearch_one_midx(oid, m, &first);
+
+		/*
+		 * first is now the position in the packfile where we
+		 * would insert the object ID if it does not exist (or the
+		 * position of the object ID if it does exist). Hence, we
+		 * consider a maximum of two objects nearby for the
+		 * abbreviation length.
+		 */
+
+		if (!match) {
+			if (nth_midxed_object_oid(&found_oid, m, first))
+				extend_abbrev_len(&found_oid, oid, &len);
+		} else if (first < num - 1) {
+			if (nth_midxed_object_oid(&found_oid, m, first + 1))
+				extend_abbrev_len(&found_oid, oid, &len);
+		}
+		if (first > 0) {
+			if (nth_midxed_object_oid(&found_oid, m, first - 1))
+				extend_abbrev_len(&found_oid, oid, &len);
+		}
+	}
+
+	*out = len;
+}
+
+static void find_abbrev_len_for_pack(struct packed_git *p,
+				     const struct object_id *oid,
+				     unsigned min_len,
+				     unsigned *out)
+{
+	int match;
+	uint32_t num, first = 0;
+	struct object_id found_oid;
+	unsigned len = min_len;
+
+	num = p->num_objects;
+	match = bsearch_pack(oid, p, &first);
+
+	/*
+	 * first is now the position in the packfile where we would insert
+	 * the object ID if it does not exist (or the position of mad->hash if
+	 * it does exist). Hence, we consider a maximum of two objects
+	 * nearby for the abbreviation length.
+	 */
+	if (!match) {
+		if (!nth_packed_object_id(&found_oid, p, first))
+			extend_abbrev_len(&found_oid, oid, &len);
+	} else if (first < num - 1) {
+		if (!nth_packed_object_id(&found_oid, p, first + 1))
+			extend_abbrev_len(&found_oid, oid, &len);
+	}
+	if (first > 0) {
+		if (!nth_packed_object_id(&found_oid, p, first - 1))
+			extend_abbrev_len(&found_oid, oid, &len);
+	}
+
+	*out = len;
+}
+
+int packfile_store_find_abbrev_len(struct packfile_store *store,
+				   const struct object_id *oid,
+				   unsigned min_len,
+				   unsigned *out)
+{
+	struct packfile_list_entry *e;
+	struct multi_pack_index *m;
+
+	m = get_multi_pack_index(store->source);
+	if (m)
+		find_abbrev_len_for_midx(m, oid, min_len, &min_len);
+
+	for (e = packfile_store_get_packs(store); e; e = e->next) {
+		if (e->pack->multi_pack_index)
+			continue;
+		if (open_pack_index(e->pack) || !e->pack->num_objects)
+			continue;
+
+		find_abbrev_len_for_pack(e->pack, oid, min_len, &min_len);
+	}
+
+	*out = min_len;
+	return 0;
+}
+
 struct add_promisor_object_data {
 	struct repository *repo;
 	struct oidset *set;