[PATCH/RFC v3 05/12] pack-objects: note about in_pack_header_size

From: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Date: Mar 8, 2018, 11:42 UTC
Message-ID: <20180308114232.10508-6-pclouds@gmail.com>
In-Reply-To: <20180308114232.10508-1-pclouds@gmail.com>

Object header in a pack is packed really tight (see pack-format.txt). Even with 8 bytes length, we need 9-10 bytes most, plus a hash (20 bytes). Which means this field only needs to store a number as big as 32 (5 bits).

This is trickier to pack tight though since a new hash algorithm is coming, the number of bits needed may quickly increase. So leave it for now.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 pack-objects.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pack-objects.h b/pack-objects.h
index 4b17402953..2ccd6359d2 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -78,7 +78,7 @@ struct object_entry {
 	unsigned long z_delta_size;	/* delta data size (compressed) */
 	uint32_t hash;			/* name hint hash */
 	unsigned int in_pack_pos;
-	unsigned char in_pack_header_size;
+	unsigned char in_pack_header_size; /* note: spare bits available! */
 	unsigned type:TYPE_BITS;
 	unsigned in_pack_type:TYPE_BITS; /* could be delta */
 	unsigned preferred_base:1; /*

-- 
2.16.2.873.g32ff258c87