From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>, Derrick Stolee <dstolee@microsoft.com>
Cc: git@vger.kernel.org, gitster@pobox.com
Subject: Re: [PATCH] cleanup: fix possible overflow errors in binary search
Date: Fri, 6 Oct 2017 10:41:12 -0400 [thread overview]
Message-ID: <bd3c5fe2-ac6a-b978-163b-da07208b879c@gmail.com> (raw)
In-Reply-To: <20171006141820.6vd3qt6iosxcgebm@sigill.intra.peff.net>
On 10/6/2017 10:18 AM, Jeff King wrote:
> On Fri, Oct 06, 2017 at 09:52:31AM -0400, Derrick Stolee wrote:
>
>> A common mistake when writing binary search is to allow possible
>> integer overflow by using the simple average:
>>
>> mid = (min + max) / 2;
>>
>> Instead, use the overflow-safe version:
>>
>> mid = min + (max - min) / 2;
> Great, thank you for picking this up!
>
>> The included changes were found using the following two greps:
>>
>> grep "/ 2;" *.c
>> grep "/ 2;" */*.c
>> grep "/2;" */*.c
> You can use[1]:
>
> git grep '/ 2;' '*.c'
>
> to have Git expand the wildcard. That catches a few extra cases in
> compat/regex/*.c. Even though it's imported code, it might be
> nice to cover those, too (since it's a possible bug, and also as a good
> example).
>
> [1] I'd actually write:
>
> git grep '/ *2;' '*.c'
>
> to do it all in one grep. :)
Thanks for the grep lesson! I knew there would be a simpler way to do
what I wanted.
>> ---
>> builtin/index-pack.c | 4 ++--
>> builtin/pack-objects.c | 2 +-
>> builtin/unpack-objects.c | 2 +-
>> cache-tree.c | 2 +-
>> packfile.c | 2 +-
>> sha1-lookup.c | 2 +-
>> sha1_name.c | 2 +-
>> string-list.c | 2 +-
>> utf8.c | 2 +-
>> xdiff/xpatience.c | 2 +-
>> 10 files changed, 11 insertions(+), 11 deletions(-)
> These all look good to me (really the only way the conversion could be
> bad is if "min" was higher than "max", and each case is just inside a
> loop condition which makes sure that is not the case).
>
> -Peff
I thought this should be simple enough. When we are all happy with the
idea of this cleanup, I'll re-roll with the missed examples.
Thanks,
-Stolee
next prev parent reply other threads:[~2017-10-06 14:41 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-25 9:54 [PATCH v2 0/5] Improve abbreviation disambiguation Derrick Stolee
2017-09-25 9:54 ` [PATCH v2 1/5] test-list-objects: List a subset of object ids Derrick Stolee
2017-09-26 9:24 ` Junio C Hamano
2017-10-05 8:42 ` Jeff King
2017-10-05 9:48 ` Junio C Hamano
2017-10-05 10:00 ` Jeff King
2017-10-05 10:16 ` Junio C Hamano
2017-10-05 12:39 ` Derrick Stolee
2017-10-06 14:11 ` Jeff King
2017-10-07 19:12 ` Derrick Stolee
2017-10-07 19:33 ` Jeff King
2017-10-08 1:46 ` Junio C Hamano
2017-09-25 9:54 ` [PATCH v2 2/5] p0008-abbrev.sh: Test find_unique_abbrev() perf Derrick Stolee
2017-09-26 9:27 ` Junio C Hamano
2017-10-05 8:55 ` Jeff King
2017-10-05 8:57 ` Jeff King
2017-09-25 9:54 ` [PATCH v2 3/5] sha1_name: Unroll len loop in find_unique_abbrev_r Derrick Stolee
2017-09-25 9:54 ` [PATCH v2 4/5] sha1_name: Parse less while finding common prefix Derrick Stolee
2017-09-25 23:42 ` Stefan Beller
2017-10-02 14:52 ` Derrick Stolee
2017-09-25 9:54 ` [PATCH v2 5/5] sha1_name: Minimize OID comparisons during disambiguation Derrick Stolee
2017-10-02 14:56 ` [PATCH v3 0/5] Improve abbreviation disambituation Derrick Stolee
2017-10-05 9:49 ` Jeff King
2017-10-02 14:56 ` [PATCH v3 1/5] test-list-objects: List a subset of object ids Derrick Stolee
2017-10-03 4:16 ` Junio C Hamano
2017-10-02 14:56 ` [PATCH v3 2/5] p0008-abbrev.sh: Test find_unique_abbrev() perf Derrick Stolee
2017-10-02 14:56 ` [PATCH v3 3/5] sha1_name: Unroll len loop in find_unique_abbrev_r Derrick Stolee
2017-10-03 10:49 ` Junio C Hamano
2017-10-03 11:26 ` Derrick Stolee
2017-10-04 6:10 ` Junio C Hamano
2017-10-04 13:06 ` Derrick Stolee
2017-10-04 6:07 ` Junio C Hamano
2017-10-04 13:19 ` Derrick Stolee
2017-10-05 1:26 ` Junio C Hamano
2017-10-05 9:13 ` Jeff King
2017-10-05 9:50 ` Junio C Hamano
2017-10-02 14:56 ` [PATCH v3 4/5] sha1_name: Parse less while finding common prefix Derrick Stolee
2017-10-04 6:14 ` Junio C Hamano
2017-10-02 14:56 ` [PATCH v3 5/5] sha1_name: Minimize OID comparisons during disambiguation Derrick Stolee
2017-10-03 15:55 ` Stefan Beller
2017-10-03 17:05 ` Derrick Stolee
2017-10-05 9:44 ` Jeff King
2017-10-06 13:52 ` [PATCH] cleanup: fix possible overflow errors in binary search Derrick Stolee
2017-10-06 14:18 ` Jeff King
2017-10-06 14:41 ` Derrick Stolee [this message]
2017-10-08 18:29 ` [PATCH v2] " Derrick Stolee
2017-10-09 13:33 ` Jeff King
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