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From: Jeff King <peff@peff.net>
To: Michael Haggerty <mhagger@alum.mit.edu>
Cc: Junio C Hamano <gitster@pobox.com>,
	Kim Gybels <kgybels@infogroep.be>,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	git@vger.kernel.org
Subject: Re: [PATCH 3/6] find_reference_location(): make function safe for empty snapshots
Date: Wed, 24 Jan 2018 15:27:54 -0500	[thread overview]
Message-ID: <20180124202754.GA7773@sigill.intra.peff.net> (raw)
In-Reply-To: <e9f9ed1944c297a68c2b76f5d4ddd73e279bd207.1516791909.git.mhagger@alum.mit.edu>

On Wed, Jan 24, 2018 at 12:14:13PM +0100, Michael Haggerty wrote:

> diff --git a/refs/packed-backend.c b/refs/packed-backend.c
> index 08698de6ea..361affd7ad 100644
> --- a/refs/packed-backend.c
> +++ b/refs/packed-backend.c
> [...]
> @@ -551,7 +553,7 @@ static const char *find_reference_location(struct snapshot *snapshot,
>  	 */
>  	const char *hi = snapshot->eof;
>  
> -	while (lo < hi) {
> +	while (lo != hi) {
>  		const char *mid, *rec;
>  		int cmp;

This tightens the binary search termination condition. If we ever did
see "hi > lo", we'd want to terminate the loop. Is that ever possible?

I think the answer is "no". Our "hi" here is an exclusive bound, so we
should never go past it via find_end_of_record() when assigning "lo".
And "hi" is always assigned from the start of the current record. That
can never cross "lo", because find_start_of_record() ensures it.

So I think it's fine, but I wanted to double check.

-Peff

  reply	other threads:[~2018-01-24 20:28 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-13 16:11 [PATCH] packed_ref_cache: don't use mmap() for small files Kim Gybels
2018-01-13 18:56 ` Johannes Schindelin
2018-01-14 19:14 ` [PATCH v2] " Kim Gybels
2018-01-15 12:17   ` [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files" Michael Haggerty
2018-01-15 12:17     ` [PATCH 1/3] SQUASH? Mention that `snapshot::buf` can be NULL for empty files Michael Haggerty
2018-01-15 12:17     ` [PATCH 2/3] create_snapshot(): exit early if the file was empty Michael Haggerty
2018-01-15 12:17     ` [PATCH 3/3] find_reference_location(): don't invoke if `snapshot->buf` is NULL Michael Haggerty
2018-01-17 20:23     ` [PATCH 0/3] Supplements to "packed_ref_cache: don't use mmap() for small files" Johannes Schindelin
2018-01-17 21:52     ` Junio C Hamano
2018-01-15 21:15 ` [PATCH] packed_ref_cache: don't use mmap() for small files Jeff King
2018-01-15 23:37   ` Kim Gybels
2018-01-15 23:52     ` Jeff King
2018-01-16 19:38       ` [PATCH v3] " Kim Gybels
2018-01-17 22:09         ` Jeff King
2018-01-21  4:41           ` Michael Haggerty
2018-01-22 19:31             ` Junio C Hamano
2018-01-24 11:05               ` Michael Haggerty
2018-01-24 11:14                 ` [PATCH 0/6] Yet another approach to handling empty snapshots Michael Haggerty
2018-01-24 11:14                   ` [PATCH 1/6] struct snapshot: store `start` rather than `header_len` Michael Haggerty
2018-01-24 20:36                     ` Jeff King
2018-01-24 11:14                   ` [PATCH 2/6] create_snapshot(): use `xmemdupz()` rather than a strbuf Michael Haggerty
2018-01-24 11:14                   ` [PATCH 3/6] find_reference_location(): make function safe for empty snapshots Michael Haggerty
2018-01-24 20:27                     ` Jeff King [this message]
2018-01-24 21:11                       ` Junio C Hamano
2018-01-24 21:34                         ` Jeff King
2018-01-24 11:14                   ` [PATCH 4/6] packed_ref_iterator_begin(): make optimization more general Michael Haggerty
2018-01-24 20:32                     ` Jeff King
2018-01-24 11:14                   ` [PATCH 5/6] load_contents(): don't try to mmap an empty file Michael Haggerty
2018-01-24 11:14                   ` [PATCH 6/6] packed_ref_cache: don't use mmap() for small files Michael Haggerty
2018-01-24 20:38                   ` [PATCH 0/6] Yet another approach to handling empty snapshots Jeff King
2018-01-24 20:54                   ` Junio C Hamano
2018-02-15 16:54                   ` Johannes Schindelin
2018-01-24 18:05                 ` [PATCH v3] packed_ref_cache: don't use mmap() for small files Junio C Hamano

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