Re: Understanding Binary Deltas within Packfile

From: Duy Nguyen <pclouds@gmail.com>
Date: Mar 20, 2018, 16:03 UTC
Message-ID: <CACsJy8ABgZy=eJ7niUysb2XZ3qUr3J+jmh_5YWZ1ZDiFCrb0tA@mail.gmail.com>
In-Reply-To: <f301d093-af93-016b-79b9-3102475260cf@arlut.utexas.edu>

On Tue, Mar 20, 2018 at 4:43 PM, Luke Robison <robison@arlut.utexas.edu> wrote:

Show 6 quoted lines

> Is there any documentation of the contents of the binary delta datain a
> packfile, and how to interpret them?  I found
> https://github.com/git/git/blob/master/Documentation/technical/pack-format.txt
> documenting the packfile itself, but the "compressed delta data" seems
> largely undocumented.  The source code of
> https://github.com/git/git/blob/master/diff-delta.c is pretty dense.

The output is consumed by patch_delta() in patch-delta.c if I'm not mistaken. This function is less than 100 lines, probably much easier to see the delta format.

Show 19 quoted lines

>  This
> is what I've got so for:
>
> +-------------+
> | Varint src_size
> | Varint trg_size
> | 1-byte inscnt
> | N-bytes up to 16 bytes of trg_buf
> |
> | A series of Operations
> |
> +-------------
>
>
> Any details on how to interpret the opcodes would be greatly appreciated.
>
> Thanks,
> Luke
>

-- 
Duy