Re: [PATCH] Show binary file size change in diff --stat

From: Rogan Dawes <lists@dawes.za.net>
Date: Apr 4, 2007, 15:51 UTC
Message-ID: <4613C97C.9050600@dawes.za.net>
In-Reply-To: <200704041540.59977.andyparkins@gmail.com>

Andy Parkins wrote:

Show 21 quoted lines

> On Wednesday 2007 April 04 14:34, Rogan Dawes wrote:
> 
>> Well, how about my comments in <45E67978.9030805@dawes.za.net>,
>> suggesting that the edit difference (number of steps required to
>> transform one to the other) would be a better indication?
> 
> Perhaps.  There is certainly a difference between:
> 
>  somefile.bin  | 1000 -> 1000 bytes
> 
> and
> 
>  somefile.bin  | 500 bytes removed, 500 bytes added
> 
>> I think it is better because it is consistent with what we currently do
>> for text files: show the number of lines added/deleted.
> 
> The thing is, "lines" is an understandable unit for a text file, so it's 
> useful to show.  I'm not sure the same is true of "bytes" for a binary file.  
> Those bytes could represent anything; the true unit of a binary file is 
> dependent on its type.

I think bytes are the only reasonable unit for a binary file, since we have no idea what a meaningful divisor may be. So, defaulting to the smallest possible unit (other than going to the bit-level) makes perfect sense.

Show 13 quoted lines

>> For binary files, it would be consistent to show the number of bytes
>> added/deleted. I have not investigated the output format for the
>> libxdiff binary patch format, but hopefully it would not be too
>> difficult to calculate the deletions and additions.
> 
> I'm inclined to agree with Johannes, while it's certainly something 
> that /could/ be shown - is it more useful?  There is no guarantee that a 
> small change in the underlying content is represented by a small change in 
> the binary diff.
> 
> As an example: compress a file, change a byte, compress it again, perform a 
> binary diff; what is that diff telling you about the change?  (My answer is: 
> not much).

Well, at least as much as the resulting sizes tell you, if not more.

Here is a counter example for a text file, where lines changed do not actually reflect the real changes in the file: the contents of an XML file being wrapped in an additional tag.

Semantically, all that has changed is an opening and closing tag. But, we still show that on a line by line basis, the entire file has changed (because the indentation changes). So you'd have n lines deleted, and n+2 lines added (for the additional opening and closing tag).

> Andy

I still maintain that showing bytes changed is the only consistent thing to do, unless we have additional logic that allows us to do "per file-type" diff statistics. Maybe .gitattributes will allow/enable this?

Regards,

Rogan

P.S. I'm not volunteering to inflict my novice C-skills on the git community, so this is really "just my 2c"