Subject: [PATCH v5 11/11] pack-objects.h: reorder members to shrink struct object_entry

From: Nguyễn Thái Ngọc Duy <[email-masked]>
Date: Sat, 17 Mar 2018 15:10:33 +0100

Previous patches leave lots of holes and padding in this struct. This
patch reorders the members and shrinks the struct down to 80 bytes
(from 136 bytes, before any field shrinking is done) with 16 bits to
spare (and a couple more in in_pack_header_size when we really run out
of bits).

Signed-off-by: Nguyễn Thái Ngọc Duy <[email-masked]>
---
 pack-objects.h | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/pack-objects.h b/pack-objects.h
index 2507b157d5..8979289f5f 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -71,35 +71,36 @@ enum dfs_state {
  */
 struct object_entry {
 	struct pack_idx_entry idx;
-	/* object uncompressed size _if_ size_valid is true */
-	uint32_t size_;
-	unsigned size_valid:1;
-	unsigned in_pack_idx:OE_IN_PACK_BITS;	/* already in pack */
+	void *delta_data;	/* cached delta (uncompressed) */
 	off_t in_pack_offset;
+	uint32_t hash;			/* name hint hash */
+	uint32_t size_;	/* object uncompressed size _if_ size_valid is true */
 	uint32_t delta_idx;	/* delta base object */
 	uint32_t delta_child_idx; /* deltified objects who bases me */
 	uint32_t delta_sibling_idx; /* other deltified objects who
 				     * uses the same base as me
 				     */
-	void *delta_data;	/* cached delta (uncompressed) */
 	uint32_t delta_size_:OE_DELTA_SIZE_BITS; /* delta data size (uncompressed) */
 	uint32_t delta_size_valid:1;
+	unsigned in_pack_idx:OE_IN_PACK_BITS;	/* already in pack */
+	unsigned size_valid:1;
 	unsigned z_delta_size:OE_Z_DELTA_BITS;
+	unsigned type_valid:1;
 	unsigned type_:TYPE_BITS;
 	unsigned in_pack_type:TYPE_BITS; /* could be delta */
-	unsigned type_valid:1;
-	uint32_t hash;			/* name hint hash */
-	unsigned char in_pack_header_size;
 	unsigned preferred_base:1; /*
 				    * we do not pack this, but is available
 				    * to be used as the base object to delta
 				    * objects against.
 				    */
 	unsigned no_try_delta:1;
+	unsigned char in_pack_header_size;
 	unsigned tagged:1; /* near the very tip of refs */
 	unsigned filled:1; /* assigned write-order */
 	unsigned dfs_state:OE_DFS_STATE_BITS;
 	unsigned depth:OE_DEPTH_BITS;
+
+	/* size: 80, bit_padding: 16 bits */
 };
 
 struct packing_data {
-- 
2.17.0.rc0.347.gf9cf61673a