The current documentation does not mention the ofs_delta pack
object type. This patch is also supposed to make the text a bit
more readable, since it moves the object entry header
description earlier.
I fixes one error in these lines:
If it is DELTA, then
20-byte base object name SHA1 (the size above is the
size of the delta data that follows).
The size given in the object header is actually the inflated size
of the delta data that follows, since the call chain goes like
this:
For delta objects:
unpack_entry()
unpack_object_header()
unpack_delta_entry()
unpack_compressed_entry()
For non-delta objects:
unpack_entry()
unpack_object_header()
unpack_compressed_entry()
unpack_compressed_entry() allocates a buffer of the size
given in its last argument, and inflates the data into
this buffer.
So all objects have in fact their inflated size given
in the packed object header.
Signed-off-by: Peter Eriksen <s022018@xxxxxxxxxxxxxx>
---
Documentation/technical/pack-format.txt | 43
++++++++++++++++--------------
1 files changed, 23 insertions(+), 20 deletions(-)
Did I understand this right especially the part
with what the length field in the packed objects
headers mean?
diff --git a/Documentation/technical/pack-format.txt
b/Documentation/technical/pack-format.txt
index aa87756..35ee01d 100644
--- a/Documentation/technical/pack-format.txt
+++ b/Documentation/technical/pack-format.txt
@@ -19,15 +19,34 @@ GIT pack format
- The header is followed by number of object entries, each of
which looks like this:
+
+ An n-byte header encoding the
+ type of the object
+ length of the object before compression
+
+ The format of the header:
+ 1-byte size extension bit (MSB)
+ type (next 3 bit)
+ size0 (lower 4-bit)
+ n-byte sizeN (as long as MSB is set, each 7-bit)
+ size0..sizeN form 4+7+7+..+7 bit integer, size0
+ is the least significant part, and sizeN is the
+ most significant part.
+
- (undeltified representation)
- n-byte type and length (3-bit type, (n-1)*7+4-bit length)
+ The header is followed by:
+
+ (for object types: commit, tree, blob, and tag)
compressed data
- (deltified representation)
- n-byte type and length (3-bit type, (n-1)*7+4-bit length)
+ (for object type ref_delta)
20-byte base object name
compressed delta data
+
+ (for object type ofs_delta)
+ n-byte offset (n*7-bit as above, but with size0 being 7 bit)
+ compressed delta data
+
Observation: length of each object is encoded in a variable
length format and is not constrained to 32-bit or anything.
@@ -92,22 +111,6 @@ trailer | | packfile checksum |
|
Pack file entry: <+
- packed object header:
- 1-byte size extension bit (MSB)
- type (next 3 bit)
- size0 (lower 4-bit)
- n-byte sizeN (as long as MSB is set, each 7-bit)
- size0..sizeN form 4+7+7+..+7 bit integer, size0
- is the least significant part, and sizeN is the
- most significant part.
- packed object data:
- If it is not DELTA, then deflated bytes (the size above
- is the size before compression).
- If it is DELTA, then
- 20-byte base object name SHA1 (the size above is the
- size of the delta data that follows).
- delta data, deflated.
-
= Version 2 pack-*.idx files support packs larger than 4 GiB, and
have some other reorganizations. They have the format:
--
1.5.5-rc3.GIT
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
