From: "René Scharfe" <l.s.r@web.de>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Junio C Hamano" <gitster@pobox.com>
Cc: Git List <git@vger.kernel.org>
Subject: Re: [PATCH 3/9] test-mergesort: add test subcommand
Date: Sun, 3 Oct 2021 12:15:21 +0200 [thread overview]
Message-ID: <850aa059-61d9-0eba-5809-e0c27a19dfb4@web.de> (raw)
In-Reply-To: <87o887q0s9.fsf@evledraar.gmail.com>
Am 02.10.21 um 10:35 schrieb Ævar Arnfjörð Bjarmason:
>
> On Fri, Oct 01 2021, Junio C Hamano wrote:
>
>> René Scharfe <l.s.r@web.de> writes:
>>
>>> +static void dist_rand(int *arr, int n, int m)
>>> +{
>>> + int i;
>>> + for (i = 0; i < n; i++)
>>> + arr[i] = rand() % m;
>>> +}
>>> ...
>>> +static void dist_shuffle(int *arr, int n, int m)
>>> +{
>>> + int i, j, k;
>>> + for (i = j = 0, k = 1; i < n; i++)
>>> + arr[i] = (rand() % m) ? (j += 2) : (k += 2);
>>> +}
>>
>> I briefly wondered if we want to seed the rand() in some way to make
>> the tests reproducible, but we'd need to ship our own rand() if we
>> wanted to go that route, which would probably be too much.
>
> Wouldn't calling srand() with some constant value suffice on most
> platforms? I'm aware of it being a NOOP and rand() always being randomly
> seeded on (IIRC) OpenBSD, but that should work on e.g. glibc.
Right, so we'd need to ship our own random number generator.
Repeatable tests are not essential (the original paper didn't mention
seeding), but shouldn't be much trouble to implement and would simplify
comparisons across versions, systems and among testers.
The only downside I can think of is that it may perhaps also simplify
over-fitting, i.e. I might find micro-tweaks that only work for our
specific rand() sequence and then misinterpret them as general
improvements..
René
next prev parent reply other threads:[~2021-10-03 10:15 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 9:07 [PATCH 0/9] mergesort: improve tests and performance René Scharfe
2021-10-01 9:10 ` [PATCH 1/9] test-mergesort: use strbuf_getline() René Scharfe
2021-10-02 9:08 ` Ævar Arnfjörð Bjarmason
2021-10-02 16:56 ` René Scharfe
2021-10-01 9:11 ` [PATCH 2/9] test-mergesort: add sort subcommand René Scharfe
2021-10-01 20:26 ` Junio C Hamano
2021-10-01 9:12 ` [PATCH 3/9] test-mergesort: add test subcommand René Scharfe
2021-10-01 20:26 ` Junio C Hamano
2021-10-02 8:35 ` Ævar Arnfjörð Bjarmason
2021-10-03 10:15 ` René Scharfe [this message]
2021-10-03 17:33 ` Junio C Hamano
2021-10-07 20:00 ` René Scharfe
2021-10-08 4:04 ` [PATCH 10/9 v2] test-mergesort: use repeatable random numbers René Scharfe
2021-10-08 4:17 ` Jeff King
2021-10-08 7:23 ` Ævar Arnfjörð Bjarmason
2021-10-08 17:30 ` René Scharfe
2021-10-08 19:00 ` Ævar Arnfjörð Bjarmason
2021-10-03 10:15 ` [PATCH 3/9] test-mergesort: add test subcommand René Scharfe
2021-10-01 9:14 ` [PATCH 4/9] test-mergesort: add generate subcommand René Scharfe
2021-10-01 9:16 ` [PATCH 5/9] test-mergesort: add unriffle mode René Scharfe
2021-10-01 9:17 ` [PATCH 6/9] test-mergesort: add unriffle_skewed mode René Scharfe
2021-10-01 9:19 ` [PATCH 7/9] p0071: measure sorting of already sorted and reversed files René Scharfe
2021-10-01 9:19 ` [PATCH 8/9] p0071: test performance of llist_mergesort() René Scharfe
2021-10-01 9:22 ` [PATCH 9/9] mergesort: use ranks stack René Scharfe
2022-01-17 17:43 ` Ævar Arnfjörð Bjarmason
2022-01-17 18:22 ` René Scharfe
2022-01-18 5:07 ` René Scharfe
2022-01-18 10:40 ` Ævar Arnfjörð Bjarmason
2022-01-18 12:27 ` René Scharfe
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