From 2dd625d022074bb677bdd5caa5146cabaf726123 Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Date: Sat, 20 Dec 2008 13:05:47 +0100
Subject: [PATCH] Speed up git notes lookup

To avoid looking up each and every commit in the notes ref's tree
object, which is very expensive, speed things up by slurping the tree
object's contents into a hash_map.

The idea fo the hashmap singleton is from David Reiss, initial
benchmarking by Jeff King.

Note: the implementation allows for arbitrary entries in the notes
tree object, ignoring those that do not reference a valid object.  This
allows you to annotate arbitrary branches, or objects.

[jc: fixed an obvious error in initialize_hash_map()]

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 notes.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 102 insertions(+), 11 deletions(-)

diff --git a/notes.c b/notes.c
index 91ec77f3f0..ad43a2ed15 100644
--- a/notes.c
+++ b/notes.c
@@ -4,16 +4,112 @@
 #include "refs.h"
 #include "utf8.h"
 #include "strbuf.h"
+#include "tree-walk.h"
+
+struct entry {
+	unsigned char commit_sha1[20];
+	unsigned char notes_sha1[20];
+};
+
+struct hash_map {
+	struct entry *entries;
+	off_t count, size;
+};
 
 static int initialized;
+static struct hash_map hash_map;
+
+static int hash_index(struct hash_map *map, const unsigned char *sha1)
+{
+	int i = ((*(unsigned int *)sha1) % map->size);
+
+	for (;;) {
+		unsigned char *current = map->entries[i].commit_sha1;
+
+		if (!hashcmp(sha1, current))
+			return i;
+
+		if (is_null_sha1(current))
+			return -1 - i;
+
+		if (++i == map->size)
+			i = 0;
+	}
+}
+
+static void add_entry(const unsigned char *commit_sha1,
+		const unsigned char *notes_sha1)
+{
+	int index;
+
+	if (hash_map.count + 1 > hash_map.size >> 1) {
+		int i, old_size = hash_map.size;
+		struct entry *old = hash_map.entries;
+
+		hash_map.size = old_size ? old_size << 1 : 64;
+		hash_map.entries = (struct entry *)
+			xcalloc(sizeof(struct entry), hash_map.size);
+
+		for (i = 0; i < old_size; i++)
+			if (!is_null_sha1(old[i].commit_sha1)) {
+				index = -1 - hash_index(&hash_map,
+						old[i].commit_sha1);
+				memcpy(hash_map.entries + index, old + i,
+					sizeof(struct entry));
+			}
+		free(old);
+	}
+
+	index = hash_index(&hash_map, commit_sha1);
+	if (index < 0) {
+		index = -1 - index;
+		hash_map.count++;
+	}
+
+	hashcpy(hash_map.entries[index].commit_sha1, commit_sha1);
+	hashcpy(hash_map.entries[index].notes_sha1, notes_sha1);
+}
+
+static void initialize_hash_map(const char *notes_ref_name)
+{
+	unsigned char sha1[20], commit_sha1[20];
+	unsigned mode;
+	struct tree_desc desc;
+	struct name_entry entry;
+	void *buf;
+
+	if (!notes_ref_name || read_ref(notes_ref_name, commit_sha1) ||
+	    get_tree_entry(commit_sha1, "", sha1, &mode))
+		return;
+
+	buf = fill_tree_descriptor(&desc, sha1);
+	if (!buf)
+		die("Could not read %s for notes-index", sha1_to_hex(sha1));
+
+	while (tree_entry(&desc, &entry))
+		if (!get_sha1(entry.path, commit_sha1))
+			add_entry(commit_sha1, entry.sha1);
+	free(buf);
+}
+
+static unsigned char *lookup_notes(const unsigned char *commit_sha1)
+{
+	int index;
+
+	if (!hash_map.size)
+		return NULL;
+
+	index = hash_index(&hash_map, commit_sha1);
+	if (index < 0)
+		return NULL;
+	return hash_map.entries[index].notes_sha1;
+}
 
 void get_commit_notes(const struct commit *commit, struct strbuf *sb,
 		const char *output_encoding)
 {
 	static const char *utf8 = "utf-8";
-	struct strbuf name = STRBUF_INIT;
-	const char *hex;
-	unsigned char sha1[20];
+	unsigned char *sha1;
 	char *msg;
 	unsigned long msgoffset, msglen;
 	enum object_type type;
@@ -24,17 +120,12 @@ void get_commit_notes(const struct commit *commit, struct strbuf *sb,
 			notes_ref_name = getenv(GIT_NOTES_REF_ENVIRONMENT);
 		else if (!notes_ref_name)
 			notes_ref_name = GIT_NOTES_DEFAULT_REF;
-		if (notes_ref_name && read_ref(notes_ref_name, sha1))
-			notes_ref_name = NULL;
+		initialize_hash_map(notes_ref_name);
 		initialized = 1;
 	}
 
-	if (!notes_ref_name)
-		return;
-
-	strbuf_addf(&name, "%s:%s", notes_ref_name,
-			sha1_to_hex(commit->object.sha1));
-	if (get_sha1(name.buf, sha1))
+	sha1 = lookup_notes(commit->object.sha1);
+	if (!sha1)
 		return;
 
 	if (!(msg = read_sha1_file(sha1, &type, &msglen)) || !msglen ||