Re: [PATCH 5/8] xdl_change_compact(): fix compaction heuristic to adjust io

From: Jeff King <peff@peff.net>
Date: Aug 11, 2016, 04:16 UTC
Message-ID: <20160811041603.xtkagaluyntawwue@sigill.intra.peff.net>
In-Reply-To: <7dea0a1e-a1b4-efe4-c86d-152f6c96604a@alum.mit.edu>

On Wed, Aug 10, 2016 at 06:58:06PM +0200, Michael Haggerty wrote:

Show 16 quoted lines

> > And it looks like rchgo[io] always ends the loop on a 0. So it seems
> > like we would just hit that condition again.
> 
> Correct...in this loop. But there is another place where `io` is
> incremented unconditionally. In the version before my changes, it is via
> the preincrement operator in this while statement conditional:
> 
> https://github.com/mhagger/git/blob/a28705da929ad746abcb34270947f738549d3246/xdiff/xdiffi.c#L502
> 
> After my changes, the unconditional increment is more obvious because I
> took it out of the while condition:
> 
> https://github.com/mhagger/git/blob/39a135da93834fd72ee923d95d0cebfe525dfe7a/xdiff/xdiffi.c#L541
> 
> (BTW, I think this is a good example of how patch 2/8 makes the code
> easier to reason about.)

Ah, yeah, I totally missed that case (and I agree the code after your 2/8 makes it much more obvious).

> I didn't do the hard work to determine whether `io` could *really* walk
> off the end of the array, but I don't see an obvious reason why it
> *couldn't*.

Yeah, I'm in agreement.

-Peff