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

From: Junio C Hamano <junkio@cox.net>
Date: Apr 4, 2007, 17:47 UTC
Message-ID: <7vbqi458vn.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <Pine.LNX.4.64.0704040935350.6730@woody.linux-foundation.org>

Linus Torvalds <torvalds@linux-foundation.org> writes:

Show 16 quoted lines

> On Wed, 4 Apr 2007, Johannes Schindelin wrote:
>> 
>> The subtle difference: your approach is _expensive_ in terms of CPU time, 
>> while the byte change approach is _dirt cheap_.
>
> Well, you could do a combination (still dirt cheap):
>  - show the size before/after (and yes, new/delete should be separate from 
>    "zero size before/after")
>  - show the size of the binary patch.
>
> No "X added bytes" vs "Y bytes deleted", just "size of binary patch". It 
> could be really small, even if 10k was deleted, or the file was totally 
> re-organized by moving chunks around.
>
> It would still be a meaningful thing to know - if only because it tells 
> you how much space the delta takes.

I agree wrt the kind of information to give, except that I am not so sure about new/delete vs zero before/after. We do not do that for a text file, and when people do care about the distinction, they would use --summary.

I often have wished that we could make --stat imply --summary; the only reason we did not do that is because the --stat option started its life as an imitation of "diffstat".

I've seen our diff-delta change its output size once. It was a nice improvement to make the delta much smaller than before, but I had to rewrite the rename similarity in diffcore not to depend on the diff-delta algorithm change, to keep it stable across diff-delta improvements (the alternative was to futz with the default threshold). I suspect we might see similar confusion if we show the delta size, depending on people's expectations. This is a very minor issue, but I thought I should mention it.

There is a machine readable output format for the same --stat information called --numstat. It currently signals the binary-ness by showing '-' instead of line count. We could extend it by showing '-' + number of bytes.

So here are some more suggestions:

 (1) --stat for binary files to show preimage and postimage
     sizes like this (if we were to do delta size -- otherwise
     drop " (.*" at the end):

	penguin.jpg |  Bin 745245 -> 660689 (delta: 4434)

 (2) --numstat for binary files to show preimage and postimage
     sizes like this:

	penguin.jpg	-745245	-660689

 (3) independent from all of the above, make --stat imply
     --summary and perhaps introduce --no-summary if people do not
     want --summary given when they say --stat;