midx: write object offsets

The final pair of chunks for the multi-pack-index file stores the object
offsets. We default to using 32-bit offsets as in the pack-index version
1 format, but if there exists an offset larger than 32-bits, we use a
trick similar to the pack-index version 2 format by storing all offsets
at least 2^31 in a 64-bit table; we use the 32-bit table to point into
that 64-bit table as necessary.

We only store these 64-bit offsets if necessary, so create a test that
manipulates a version 2 pack-index to fake a large offset. This allows
us to test that the large offset table is created, but the data does not
match the actual packfile offsets. The multi-pack-index offset does match
the (corrupted) pack-index offset, so a future feature will compare these
offsets during a 'verify' step.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/midx.h b/midx.h
index 8572cf0f4b..e15966272f 100644
--- a/midx.h
+++ b/midx.h
@@ -17,6 +17,8 @@ struct multi_pack_index {
 	const unsigned char *chunk_pack_names;
 	const uint32_t *chunk_oid_fanout;
 	const unsigned char *chunk_oid_lookup;
+	const unsigned char *chunk_object_offsets;
+	const unsigned char *chunk_large_offsets;
 
 	const char **pack_names;
 	char object_dir[FLEX_ARRAY];