From: "Daniel Shahaf" <d.s@daniel.shahaf.name>
To: zsh-workers@zsh.org
Subject: Re: [PATCH] zsh/random module [UPDATED]
Date: Thu, 24 Nov 2022 00:17:57 +0000 [thread overview]
Message-ID: <41712a61-75ab-4825-bbbc-d223823229ea@app.fastmail.com> (raw)
In-Reply-To: <aec52e64-dcd2-4893-8fca-4128e590e12b@app.fastmail.com>
Daniel Shahaf wrote on Wed, 23 Nov 2022 23:54 +00:00:
> dana wrote on Wed, 23 Nov 2022 21:42 +00:00:
>> On Wed 23 Nov 2022, at 13:46, Daniel Shahaf wrote:
>>> Oh, and bump that 16 to something 3 or 4 times as big, because a 1/65536
>>> chance isn't really enough in a world where automated builds (CI,
>>> distros' QA, etc.) is a thing.
>>
>> I feel like it should be very nearly impossible for a test to fail just for
>> randomness reasons. Maybe it's over-kill but in my draft reply to the patch i
>> was going to suggest something like this:
>>
>> () {
>> repeat $(( 10 ** 5 )); do
>> getrandom -L4 -U5 -c64 -a tmpa
>> [[ $tmpa[(r)5] == 5 ]] && return 0
>> done
>> return 1
>> }
>>
>
> No maybe about it :)
>
> With these parameters, the probability of a false positive is 2 to the
> power of minus the overall number of iterations, i.e., 2**(-6.4 million),
> which is 1/[a number that has 1.9M decimal digits].
>
> To be clear, it's not 1/1.9M, which is about the probability of a random
> Londoner being at 10 Downing Street right now. It's 1/[10 ** 1.9M],
> which is about the probability of correctly guessing the genders of all
> Londoners.
To be clear, I don't mean guessing the gender /ratio/. I mean filling
a spreadsheet with one row for each Londoner and having to guess each and
every row correctly, without any information about the particular Londoner.
> If you converted the entire Earth's mass to CPUs and ran «getrandom -L4
> -U5 -c64» on it repeatedly until Sol died, and the CPUs all operated at
> 4GHz, and there were no bugs in anything, the chance of getting a single
> run to not return a 5 would still be something like a billion to one
> (give or take several zeroes depending on CPU mass, the argument to -c,
> and so on).
>
> That's why in practice, if a single -c64 call ever doesn't return a 5,
> it's safe to assume there's a bug.
>
> Conversely, if you actually retain those 6.4 million iterations, what's
> the probability that the outer loop will return 0 on the first iteration
> and then a gamma ray will flip that to 0?
next prev parent reply other threads:[~2022-11-24 0:18 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-02 17:13 [PATCH] zsh/random module Clinton Bunch
2022-11-03 17:50 ` Bart Schaefer
2022-11-04 3:17 ` dana
2022-11-04 6:22 ` Clinton Bunch
2022-11-04 7:27 ` dana
2022-11-04 12:57 ` Clinton Bunch
2022-11-08 0:18 ` [PATCH] zsh/random module [UPDATED] Clinton Bunch
2022-11-18 14:30 ` Clinton Bunch
2022-11-19 6:42 ` Lawrence Velázquez
2022-11-18 16:23 ` Stephane Chazelas
2022-11-18 17:08 ` Clinton Bunch
2022-11-18 18:12 ` Stephane Chazelas
2022-11-18 18:38 ` Clinton Bunch
2022-11-23 19:52 ` Daniel Shahaf
2022-11-24 16:19 ` Stephane Chazelas
2022-11-24 16:30 ` Roman Perepelitsa
2022-11-24 22:39 ` Clinton Bunch
2022-11-25 8:53 ` Stephane Chazelas
2022-11-25 9:40 ` Stephane Chazelas
2022-11-28 16:37 ` further discussion of zsh/random (was [PATCH] zsh/random module [UPDATED]) Clinton Bunch
2022-11-21 1:07 ` [PATCH] zsh/random module [UPDATED] Matthew Martin
2022-11-21 1:59 ` Clinton Bunch
2022-11-21 2:21 ` Matthew Martin
2022-11-21 2:57 ` Clinton Bunch
2022-11-21 3:14 ` Lawrence Velázquez
2022-11-21 4:17 ` Bart Schaefer
2022-11-21 5:05 ` Clinton Bunch
2022-11-22 13:42 ` dana
2022-11-23 19:49 ` Daniel Shahaf
2022-11-22 17:44 ` Oliver Kiddle
2022-11-22 19:48 ` Clinton Bunch
2022-11-23 1:23 ` Matthew Martin
2022-11-23 2:58 ` Clinton Bunch
2022-11-23 4:14 ` Matthew Martin
2022-11-23 13:41 ` Clinton Bunch
2022-11-23 20:33 ` Daniel Shahaf
2022-11-23 21:42 ` dana
2022-11-23 23:54 ` Daniel Shahaf
2022-11-24 0:17 ` Daniel Shahaf [this message]
2022-11-24 1:05 ` dana
2022-11-24 13:52 ` Clinton Bunch
2022-11-23 19:46 ` Daniel Shahaf
2022-11-24 2:58 ` Clinton Bunch
2022-11-24 10:07 ` nimaje+zml
2022-11-24 13:19 ` Clinton Bunch
2022-11-24 14:33 ` Clinton Bunch
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=41712a61-75ab-4825-bbbc-d223823229ea@app.fastmail.com \
--to=d.s@daniel.shahaf.name \
--cc=zsh-workers@zsh.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/zsh/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).