Merge branch 'ds/find-unique-abbrev-optim'

Optimize the code to find shortest unique prefix of object names.

* ds/find-unique-abbrev-optim:
  sha1_name: minimize OID comparisons during disambiguation
  sha1_name: parse less while finding common prefix
  sha1_name: unroll len loop in find_unique_abbrev_r()
  p4211-line-log.sh: add log --online --raw --parents perf test

Author: gitster

sha1_name.c

@@ -153,7 +153,9 @@ static void unique_in_pack(struct packed_git *p,
 	uint32_t num, last, i, first = 0;
 	const struct object_id *current = NULL;
 
-	open_pack_index(p);
+	if (open_pack_index(p) || !p->num_objects)
+		return;
+
 	num = p->num_objects;
 	last = num;
 	while (first < last) {
@@ -474,10 +476,104 @@ static unsigned msb(unsigned long val)
 	return r;
 }
 
-int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
+struct min_abbrev_data {
+	unsigned int init_len;
+	unsigned int cur_len;
+	char *hex;
+	const unsigned char *hash;
+};
+
+static inline char get_hex_char_from_oid(const struct object_id *oid,
+					 unsigned int pos)
 {
-	int status, exists;
+	static const char hex[] = "0123456789abcdef";
 
+	if ((pos & 1) == 0)
+		return hex[oid->hash[pos >> 1] >> 4];
+	else
+		return hex[oid->hash[pos >> 1] & 0xf];
+}
+
+static int extend_abbrev_len(const struct object_id *oid, void *cb_data)
+{
+	struct min_abbrev_data *mad = cb_data;
+
+	unsigned int i = mad->init_len;
+	while (mad->hex[i] && mad->hex[i] == get_hex_char_from_oid(oid, i))
+		i++;
+
+	if (i < GIT_MAX_RAWSZ && i >= mad->cur_len)
+		mad->cur_len = i + 1;
+
+	return 0;
+}
+
+static void find_abbrev_len_for_pack(struct packed_git *p,
+				     struct min_abbrev_data *mad)
+{
+	int match = 0;
+	uint32_t num, last, first = 0;
+	struct object_id oid;
+
+	if (open_pack_index(p) || !p->num_objects)
+		return;
+
+	num = p->num_objects;
+	last = num;
+	while (first < last) {
+		uint32_t mid = first + (last - first) / 2;
+		const unsigned char *current;
+		int cmp;
+
+		current = nth_packed_object_sha1(p, mid);
+		cmp = hashcmp(mad->hash, current);
+		if (!cmp) {
+			match = 1;
+			first = mid;
+			break;
+		}
+		if (cmp > 0) {
+			first = mid + 1;
+			continue;
+		}
+		last = mid;
+	}
+
+	/*
+	 * first is now the position in the packfile where we would insert
+	 * mad->hash if it does not exist (or the position of mad->hash if
+	 * it does exist). Hence, we consider a maximum of three objects
+	 * nearby for the abbreviation length.
+	 */
+	mad->init_len = 0;
+	if (!match) {
+		nth_packed_object_oid(&oid, p, first);
+		extend_abbrev_len(&oid, mad);
+	} else if (first < num - 1) {
+		nth_packed_object_oid(&oid, p, first + 1);
+		extend_abbrev_len(&oid, mad);
+	}
+	if (first > 0) {
+		nth_packed_object_oid(&oid, p, first - 1);
+		extend_abbrev_len(&oid, mad);
+	}
+	mad->init_len = mad->cur_len;
+}
+
+static void find_abbrev_len_packed(struct min_abbrev_data *mad)
+{
+	struct packed_git *p;
+
+	prepare_packed_git();
+	for (p = packed_git; p; p = p->next)
+		find_abbrev_len_for_pack(p, mad);
+}
+
+int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
+{
+	struct disambiguate_state ds;
+	struct min_abbrev_data mad;
+	struct object_id oid_ret;
 	if (len < 0) {
 		unsigned long count = approximate_object_count();
 		/*
@@ -503,19 +599,26 @@ int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
 	sha1_to_hex_r(hex, sha1);
 	if (len == GIT_SHA1_HEXSZ || !len)
 		return GIT_SHA1_HEXSZ;
-	exists = has_sha1_file(sha1);
-	while (len < GIT_SHA1_HEXSZ) {
-		struct object_id oid_ret;
-		status = get_short_oid(hex, len, &oid_ret, GET_OID_QUIETLY);
-		if (exists
-		    ? !status
-		    : status == SHORT_NAME_NOT_FOUND) {
-			hex[len] = 0;
-			return len;
-		}
-		len++;
-	}
-	return len;
+
+	mad.init_len = len;
+	mad.cur_len = len;
+	mad.hex = hex;
+	mad.hash = sha1;
+
+	find_abbrev_len_packed(&mad);
+
+	if (init_object_disambiguation(hex, mad.cur_len, &ds) < 0)
+		return -1;
+
+	ds.fn = extend_abbrev_len;
+	ds.always_call_fn = 1;
+	ds.cb_data = (void *)&mad;
+
+	find_short_object_filename(&ds);
+	(void)finish_object_disambiguation(&ds, &oid_ret);
+
+	hex[mad.cur_len] = 0;
+	return mad.cur_len;
 }
 
 const char *find_unique_abbrev(const unsigned char *sha1, int len)

t/perf/p4211-line-log.sh

@@ -31,4 +31,8 @@ test_perf 'git log -L (renames on)' '
 	git log -M -L 1:"$file" >/dev/null
 '
 
+test_perf 'git log --oneline --raw --parents' '
+	git log --oneline --raw --parents >/dev/null
+'
+
 test_done