From: Junio C Hamano <gitster@pobox.com>
To: Michael Haggerty <mhagger@alum.mit.edu>
Cc: git@vger.kernel.org, "Stefan Beller" <sbeller@google.com>,
"Jeff King" <peff@peff.net>, "Jakub Narębski" <jnareb@gmail.com>,
"Jacob Keller" <jacob.keller@gmail.com>
Subject: Re: [PATCH 5/8] xdl_change_compact(): fix compaction heuristic to adjust io
Date: Thu, 04 Aug 2016 11:43:54 -0700 [thread overview]
Message-ID: <xmqqshuk2x3p.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <ae7590443737a3996ec4973fd868ce89dc78a576.1470259583.git.mhagger@alum.mit.edu> (Michael Haggerty's message of "Thu, 4 Aug 2016 00:00:33 +0200")
Michael Haggerty <mhagger@alum.mit.edu> writes:
> The code branch used for the compaction heuristic incorrectly forgot to
> keep io in sync while the group was shifted. I think that could have
> led to reading past the end of the rchgo array.
I had to read the first sentence three times as "incorrectly forgot"
was a bit strange thing to say (as if there is a situation where
'forgetting to do' is the correct thing to do, but in that case we
would phrase it to stress that not doing is a deliberate choice,
e.g. 'refraining from doing'). Perhaps s/incorrectly // is the
simplest readability improvement?
> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
> ---
> I didn't actually try to verify the presence of a bug, because it
> seems like more work than worthwhile. But here is my reasoning:
>
> If io is not decremented correctly during one iteration of the outer
> `while` loop, then it will loose sync with the `end` counter. In
> particular it will be too large.
>
> Suppose that the next iterations of the outer `while` loop (i.e.,
> processing the next block of add/delete lines) don't have any sliders.
> Then the `io` counter would be incremented by the number of
> non-changed lines in xdf, which is the same as the number of
> non-changed lines in xdfo that *should have* followed the group that
> experienced the malfunction. But since `io` was too large at the end
> of that iteration, it will be incremented past the end of the
> xdfo->rchg array, and will try to read that memory illegally.
I agree with Peff that these should be in the log message.
next prev parent reply other threads:[~2016-08-04 18:44 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-03 22:00 [PATCH 0/8] Better heuristics make prettier diffs Michael Haggerty
2016-08-03 22:00 ` [PATCH 1/8] xdl_change_compact(): rename some local variables for clarity Michael Haggerty
2016-08-04 7:06 ` Jeff King
2016-08-04 18:24 ` Junio C Hamano
2016-08-13 19:38 ` Michael Haggerty
2016-08-14 12:26 ` Jeff King
2016-08-03 22:00 ` [PATCH 2/8] xdl_change_compact(): clarify code Michael Haggerty
2016-08-03 22:11 ` Stefan Beller
2016-08-03 23:14 ` Michael Haggerty
2016-08-03 23:50 ` Stefan Beller
2016-08-04 7:13 ` Jeff King
2016-08-10 16:39 ` Michael Haggerty
2016-08-10 16:58 ` Stefan Beller
2016-08-03 22:00 ` [PATCH 3/8] xdl_change_compact(): rename i to end Michael Haggerty
2016-08-04 7:16 ` Jeff King
2016-08-03 22:00 ` [PATCH 4/8] xdl_change_compact(): do one final shift or the other, not both Michael Haggerty
2016-08-03 22:00 ` [PATCH 5/8] xdl_change_compact(): fix compaction heuristic to adjust io Michael Haggerty
2016-08-04 7:27 ` Jeff King
2016-08-10 16:58 ` Michael Haggerty
2016-08-10 17:09 ` Michael Haggerty
2016-08-11 4:16 ` Jeff King
2016-08-04 18:43 ` Junio C Hamano [this message]
2016-08-10 17:13 ` Michael Haggerty
2016-08-03 22:00 ` [PATCH 6/8] xdl_change_compact(): keep track of the earliest end Michael Haggerty
2016-08-04 18:46 ` Junio C Hamano
2016-08-10 17:16 ` Michael Haggerty
2016-08-03 22:00 ` [PATCH 7/8] is_blank_line: take a single xrecord_t as argument Michael Haggerty
2016-08-04 18:48 ` Junio C Hamano
2016-08-03 22:00 ` [PATCH 8/8] diff: improve positioning of add/delete blocks in diffs Michael Haggerty
2016-08-03 22:29 ` Jacob Keller
2016-08-03 22:36 ` Michael Haggerty
2016-08-04 4:47 ` Jacob Keller
2016-08-04 19:39 ` Junio C Hamano
2016-08-10 19:01 ` Michael Haggerty
2016-08-10 21:28 ` Junio C Hamano
2016-08-03 22:30 ` Stefan Beller
2016-08-03 22:41 ` Michael Haggerty
2016-08-03 22:51 ` Stefan Beller
2016-08-03 23:30 ` Michael Haggerty
2016-08-04 0:04 ` Stefan Beller
2016-08-10 19:12 ` Michael Haggerty
2016-08-04 7:56 ` Jeff King
2016-08-04 16:55 ` Stefan Beller
2016-08-04 19:47 ` Junio C Hamano
2016-08-13 0:09 ` Michael Haggerty
2016-08-12 23:25 ` Michael Haggerty
2016-08-13 8:59 ` Jeff King
2016-08-13 15:59 ` Junio C Hamano
2016-08-14 7:21 ` Jacob Keller
2016-08-15 6:33 ` Stefan Beller
2016-08-15 20:24 ` Junio C Hamano
2016-08-04 19:52 ` Junio C Hamano
2016-08-13 0:11 ` Michael Haggerty
2016-08-03 22:08 ` [PATCH 0/8] Better heuristics make prettier diffs Michael Haggerty
2016-08-04 7:38 ` Jeff King
2016-08-04 19:54 ` Junio C Hamano
2016-08-04 20:01 ` Jeff King
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