1 files changed, 84 insertions, 3 deletions

diff --git a/sha1_file.c b/sha1_file.c
index 110d696213..b0b21776e7 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1352,6 +1352,87 @@ static void *unpack_compressed_entry(struct packed_git *p,
 	return buffer;
 }
 
+#define MAX_DELTA_CACHE (256)
+
+static size_t delta_base_cached;
+static struct delta_base_cache_entry {
+	struct packed_git *p;
+	off_t base_offset;
+	unsigned long size;
+	void *data;
+	enum object_type type;
+} delta_base_cache[MAX_DELTA_CACHE];
+
+static unsigned long pack_entry_hash(struct packed_git *p, off_t base_offset)
+{
+	unsigned long hash;
+
+	hash = (unsigned long)p + (unsigned long)base_offset;
+	hash += (hash >> 8) + (hash >> 16);
+	return hash & 0xff;
+}
+
+static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
+	unsigned long *base_size, enum object_type *type, int keep_cache)
+{
+	void *ret;
+	unsigned long hash = pack_entry_hash(p, base_offset);
+	struct delta_base_cache_entry *ent = delta_base_cache + hash;
+
+	ret = ent->data;
+	if (ret && ent->p == p && ent->base_offset == base_offset)
+		goto found_cache_entry;
+	return unpack_entry(p, base_offset, type, base_size);
+
+found_cache_entry:
+	if (!keep_cache) {
+		ent->data = NULL;
+		delta_base_cached -= ent->size;
+	}
+	else {
+		ret = xmalloc(ent->size + 1);
+		memcpy(ret, ent->data, ent->size);
+		((char *)ret)[ent->size] = 0;
+	}
+	*type = ent->type;
+	*base_size = ent->size;
+	return ret;
+}
+
+static inline void release_delta_base_cache(struct delta_base_cache_entry *ent)
+{
+	if (ent->data) {
+		free(ent->data);
+		ent->data = NULL;
+		delta_base_cached -= ent->size;
+	}
+}
+
+static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
+	void *base, unsigned long base_size, enum object_type type)
+{
+	unsigned long i, hash = pack_entry_hash(p, base_offset);
+	struct delta_base_cache_entry *ent = delta_base_cache + hash;
+
+	release_delta_base_cache(ent);
+	delta_base_cached += base_size;
+	for (i = 0; delta_base_cached > delta_base_cache_limit
+		&& i < ARRAY_SIZE(delta_base_cache); i++) {
+		struct delta_base_cache_entry *f = delta_base_cache + i;
+		if (f->type == OBJ_BLOB)
+			release_delta_base_cache(f);
+	}
+	for (i = 0; delta_base_cached > delta_base_cache_limit
+		&& i < ARRAY_SIZE(delta_base_cache); i++)
+		release_delta_base_cache(delta_base_cache + i);
+
+	ent->p = p;
+	ent->base_offset = base_offset;
+	ent->type = type;
+	ent->data = base;
+	ent->size = base_size;
+}
+
 static void *unpack_delta_entry(struct packed_git *p,
 				struct pack_window **w_curs,
 				off_t curpos,
@@ -1365,7 +1446,7 @@ static void *unpack_delta_entry(struct packed_git *p,
 	off_t base_offset;
 
 	base_offset = get_delta_base(p, w_curs, &curpos, *type, obj_offset);
-	base = unpack_entry(p, base_offset, type, &base_size);
+	base = cache_or_unpack_entry(p, base_offset, &base_size, type, 0);
 	if (!base)
 		die("failed to read delta base object"
 		    " at %"PRIuMAX" from %s",
@@ -1378,7 +1459,7 @@ static void *unpack_delta_entry(struct packed_git *p,
 	if (!result)
 		die("failed to apply delta");
 	free(delta_data);
-	free(base);
+	add_delta_base_cache(p, base_offset, base, base_size, *type);
 	return result;
 }
 
@@ -1562,7 +1643,7 @@ static void *read_packed_sha1(const unsigned char *sha1,
 	if (!find_pack_entry(sha1, &e, NULL))
 		return NULL;
 	else
-		return unpack_entry(e.p, e.offset, type, size);
+		return cache_or_unpack_entry(e.p, e.offset, size, type, 1);
 }
 
 /*