Re: [PATCH 1/8] xdl_change_compact(): rename some local variables for clarity

[Michael Haggerty <mhagger@alum.mit.edu>]

On 08/04/2016 09:06 AM, Jeff King wrote:
> On Thu, Aug 04, 2016 at 12:00:29AM +0200, Michael Haggerty wrote:
> 
>> * ix -> i
>> * ixo -> io
>> * ixs -> start
>> * grpsiz -> groupsize
> 
> After your change, I immediately understand three of them. But what is
> "io"?

The (pre-existing) convention in this function is that variable names
dealing with the "other" file have a trailing "o"; e.g., (xdf, xdfo),
(rchg, rchgo). There used to also be (i, io), the indexes tracking the
current line number in the file and the other file. But I renamed "i".

At first I was just going to add a comment for variable "io", but in
trying to figure out its exact semantics I realized that this code is
still pretty hard to follow. Part of the problem is that "the line in
the other file corresponding to a line in the to-be-compacted file" is
not a well-defined concept. In fact it is *groups of lines* that
correlate with each other. So I totally refactored the function, using a

    struct group {
            long start, end;
    };

as a kind of a cursor used to iterate through the groups on both sides.
I think the result is a lot easier to read, and while refactoring I
found and fixed another bug in the pre-existing code :-O

I hope to have v2 out soon.

Michael