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

Linus Torvalds [off-list ref] writes:

On Wed, 4 Apr 2007, Johannes Schindelin wrote:

quoted

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;