Question about the pack OBJ_OFS_DELTA format

Hi all,

I'm trying to implement the Git pack format. Parsing the index file and unpacking undeltified objects already works. However I'm unable to get the offset, if the type is OBJ_OFS_DELTA.

The very much work-in-progress Go code and data can be found here: https://github.com/erikfastermann/notes/tree/wip/git

From the docs (https://git-scm.com/docs/pack-format) I assume, that the offset is a variable length integer, like the size. However my caclulation leads to a illogical result.

When trying the hash 8c40ff4767d973b672fe5aa431cb8ba0593dd26a with:

git verify-pack -v pack.pack

I get: offset: 138650 size: 30.

The base object 9b25d441c1bf358af01edc4eeba65870581a5ac1 (shown by verify-pack) has the offset 136887, which I think means the delta should be: 138650 - 136887 = 1763.

Using the command:

dd skip=138650 count=4 if=pack.pack bs=1 status=none | hexdump -C

I get: ee 01 8c 63

The first two bytes, the type and the size are correctly computed.

So the next varint should be the offset.

8c: 10001100 --- 63: 01100011

-> 1100011_0001100

-> 12684 ???

The result is the same when calculating it manually and with my program.

I probably have some crucial misunderstanding about the format, so a clarification would be nice.

Thank you for your help.

Erik