Re: [PATCH 06/10] pack-objects: learn about pack index version 2

Support for large packs exceeding 31 bits in size won't impose an index
size bloat for packs within that range that don't need a 64-bit offset.
And because newer objects which are likely to be the most frequently used
are located at the beginning of the pack, they won't pay the 64-bit offset
lookup at run time either even if the pack is large.

Right now an index version 2 is created only when the biggest offset in a
pack reaches 31 bits.  It might be a good idea to always use index version
2 eventually to benefit from the CRC32 it contains when reusing pack data
while repacking.
...

@@ -582,6 +602,18 @@ static void write_index_file(void)
 	struct object_entry **list = sorted_by_sha;
 	struct object_entry **last = list + nr_result;
 	uint32_t array[256];
+	uint32_t index_version;
+
+	/* if last object's offset is >= 2^31 we should use index V2 */
+	index_version = (objects[nr_result-1].offset >> 31) ? 2 : 1;