Tony Finch

unix / internet / open source software bodger
• 🏳️‍🌈🇪🇺🇬🇧 • he/they • 🚴 • 🦀 • 💉😷 • 🏳️‍⚧️ • 🇺🇦 • 🇵🇸 • ✊🏿 • tfr

WEB: https://dotat.at
EMAIL: [email protected]
HOME: Cambridge
ELSEWHERE: https://dotat.at/social.html

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Last Notes

2026-08-13 01:58:04 GMT

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fun! i like the way you have both o.g. fisher-yates and credit durstenfeld’s version properly :-)
i guess you might enjoy my notes on shuffles https://dotat.at/@/2025-12-25-shuffle.html
worth noting that the sort shuffle is likely to crash (in C it’s undefined behaviour, good luck with the nasal demons) (rust says it can panic) (ecmascript says it’s implementation-defined what sort will do if the comparator is badly behaved; dunno how forgiving it is in practice!)

2026-07-28 21:34:52 GMT

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oh right, _three_ rekeying loops! the base crng rekeys itself and the per-cpu rngs, and each per-cpu rng rekeys itself and produces output (slide 25)
https://fsn1.your-objectstorage.com/drum/media_attachments/files/116/999/748/875/437/520/original/5ffac4d3f5e938e3.png

2026-07-28 20:49:05 GMT

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i think there are two rekeying loops: the first blocks of blake2s output rekeys the hash, and the first 32 bytes from chacha20 rekeys the cipher stream - slides 20-25 of https://www.zx2c4.com/projects/linux-rng-5.17-5.18/inside-linux-kernel-rng-presentation-sept-13-2022.pdf
(i re-checked because i thought it was unlikely that per-cpu data is fed back to the global state, for locking reasons)

2026-07-21 20:09:46 GMT

what ios mastodon clients are good?
i’m annoyed by ivory’s crappy ui for filters, which spams the server requesting userpics that i don’t want to see, and pegs the rate limiter
i’ve reported it as a bug but they don’t seem to be making improvements to ivory so i should probably look elsewhere

2026-07-17 20:42:05 GMT

from my link log —
Earth rotation records spur October vote to avert negative leap second.
https://www.techtimes.com/articles/320185/20260711/earth-rotation-records-spur-october-vote-avert-negative-leap-second.htm
saved 2026-07-17 https://dotat.at/:/09RM6.html

2026-07-14 14:42:04 GMT

from my link log —
Intel underestimates fsin error bounds by 1.3 quintillion.
https://randomascii.wordpress.com/2014/10/09/intel-underestimates-error-bounds-by-1-3-quintillion/
saved 2026-07-13 https://dotat.at/:/SL0J7.html

2026-06-16 12:45:42 GMT

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not too shabby!
Anthropeum.com · Jun 16 2026
🟩🟩🟩🟨🟩🟩🟩🟩🟥🟩
68,013 · top 7% of players today!

2026-06-15 00:09:05 GMT

this game is hard! i mostly got the right continent or millennium but not often much better than that
Anthropeum.com · Jun 15 2026
🟨🟩🟨🟨🟩🟩🟨🟥🟨🟩
58,923 · top 34% of players today!

2026-05-04 17:30:31 GMT

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was it you that did a thread on twitter years ago about the grid-like wall panels used in trek and b5 and aliens that were something like repurposed drying racks?

2026-05-02 22:33:21 GMT

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how would i find that page?

2026-05-02 20:47:29 GMT

is there a way on wikipedia to reset all of my account settings to the defaults?
i have a mess of display preferences that don’t work properly and i’m pretty sure there are some old settings in my account that the current ui doesn’t expose
at least, anything i do to change the font size has no effect

2026-04-17 19:28:03 GMT

“lunar hay fever” seems like a weird way to downplay acute silicosis https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/The_toxic_side_of_the_Moon

2026-02-25 18:42:03 GMT

from my link log —
Turing completeness of GNU find: from mkdir-assisted loops to standalone computation.
https://arxiv.org/abs/2602.20762
saved 2026-02-25 https://dotat.at/:/XR86F.html

2026-01-30 19:16:38 GMT

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i don’t remember seeing anything like that but it sounds right up my street

2026-01-02 18:42:02 GMT

from my link log —
The HP-35.
http://codex99.com/design/the-hp35.html
saved 2020-12-13 https://dotat.at/:/F9KEM.html

2025-11-12 19:02:07 GMT

heh https://h4x0r.org/funreliable/
https://fsn1.your-objectstorage.com/drum/media_attachments/files/115/538/272/175/013/876/original/a80c4a14377e6064.png

2025-09-20 20:42:03 GMT

from my link log —
Pnut: a C to POSIX shell compiler.
https://pnut.sh/
saved 2025-09-09 https://dotat.at/:/CPX64.html

2025-08-31 00:49:01 GMT

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have you seen guy steele’s talk on computer science metanotation? https://groups.csail.mit.edu/mac/users/gjs/6.945/readings/Steele-MIT-April-2017.pdf https://youtu.be/dCuZkaaou0Q

2025-08-08 11:58:33 GMT

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otoh, it’s wonderful to be remembered for something that’s both beautiful and useful, better than not to be remembered at all!

2025-08-08 11:51:42 GMT

john venn’s memorial window in gonville & caius college dining hall
https://fsn1.your-objectstorage.com/drum/media_attachments/files/114/992/997/957/868/349/original/9d6169f493b114b4.jpeg

2025-07-08 07:32:08 GMT

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this also has the abstract “No.” https://cds.cern.ch/record/242413/

2025-07-02 02:28:27 GMT

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I fear my internal monologue will use that voice when I read RFCs in the future…

2025-05-01 14:06:27 GMT

“due to a problem at Space-Track, the data portal of the US military tracking network, there have been no orbit updates since April 28. Hopefully orbit updates will resume soon, so that we can run new forecasts”
https://sattrackcam.blogspot.com/2025/04/kosmos-842-descent-craft-reentry.html

2025-04-29 19:26:07 GMT

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bentley & mcilroy, “engineering a sort function” says that was an old trick in 1993!
“Although Quicksort is efficient for large arrays, its overhead can be severe for small arrays. Hence we use the old trick of sorting small subarrays by insertion sort.”

2025-04-17 11:42:02 GMT

linkspam!
Database protocols are underwhelming.
https://byroot.github.io/performance/2025/03/21/database-protocols.html
saved 2025-03-25 https://dotat.at/:/9LRWW.html

2025-04-11 07:10:11 GMT

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that’s surprisingly slow from boringssl! what version numbers are you running?

2025-03-30 18:45:40 GMT

wow, 150 TB nvme storage modules the size of a 3.5” drive sled
who remembers the Sun X4500 “thumper” with 48 drives in 4U? i looked it up to remind myself of the capacity and the drives were only 0.5 TB each back then!
https://mendeddrum.org/system/media_attachments/files/114/252/863/062/739/508/original/9a3661d32e89b357.jpeg

2025-03-08 15:42:02 GMT

https://developers.redhat.com/articles/2024/12/11/making-memcpynull-null-0-well-defined - Making memcpy(NULL, NULL, 0) well-defined.

2025-01-24 15:42:02 GMT

https://www.bryanbraun.com/2024/10/25/before-you-buy-a-domain-name-first-check-to-see-if-its-haunted/ - Before you buy a domain name, first check to see if it's haunted.

2025-01-16 18:42:01 GMT

https://arxiv.org/abs/2310.09423 - QUIC is not quick enough over fast internet.

2025-01-11 09:42:02 GMT

2021 retro-link! https://lo.calho.st/posts/black-magic-buffer/ - Using black magic to make a fast circular buffer.

2024-11-29 21:42:02 GMT

https://okmij.org/ftp/ML/generalization.html - How OCaml type checker works, or, what polymorphism and garbage collection have in common.

2024-11-24 12:42:02 GMT

https://blog.dshr.org/2024/07/x-window-system-at-40.html - The X window system at 40.

2024-11-20 15:42:02 GMT

https://www.philpem.me.uk/code/3b1emu - FreeBee: AT&T 3B1 UNIX PC emulator.

2024-11-18 09:42:02 GMT

https://www.memorysafety.org/blog/rustls-performance-outperforms/ - Rustls outperforms OpenSSL and BoringSSL.

2024-10-29 21:42:02 GMT

https://www.unsw.edu.au/newsroom/news/2024/05/Ultrasonic_cold_brew_coffee_ready_under_three_minutes - Ultrasonic cold brew coffee.

2024-10-29 02:06:14 GMT

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i’m not even sure the internet is layered in the sense of OSI because there are so many cases where configuration for one layer is carried in a different layer which i am pretty sure OSI would not permi

2024-10-29 01:56:14 GMT

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truth https://dotat.at/@/2024-03-26-iso-osi-usw.html

2024-10-28 21:42:02 GMT

https://protomaps.com/ - Protomaps: an open source map of the world, deployable as a single static file.

2024-10-25 14:42:02 GMT

https://archive.org/details/byte-magazine-1983-08 - Byte magazine August 1983: The C Language.

2024-10-09 08:42:02 GMT

https://shadowoneboxing.wordpress.com/2024/07/02/objective-tests-for-aphantasia/ - Objective tests for aphantasia.

2024-10-08 21:01:35 GMT

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yeah
there’s a nice summary at https://domainincite.com/30406-five-times-icann-deleted-a-cctld-and-what-it-means-for-io
the crucial thing is how Mauritius decides to handle the territory
if i were them, i would arrange to keep chagos separate enough that ISO 3166 MA agree it can continue to have its own code, and name chagos so it can keep the code IO
then insist to IANA that chagos should have sovereign control over the .io TLD, while keeping everything working
then use the income to compensate the chagossians

2024-10-03 20:42:02 GMT

2021 retro-link! https://berthub.eu/articles/posts/cybersecurity-is-like-food-safety/ - Cybersecurity is like food safety: digital HACCP.

2024-10-01 23:44:01 GMT

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oh and re your point about userland csprng being bad, i agree, though i did not strongly emphasise the point in my blog post
the reason i did this benchmark was to see whether i could easily justify using getrandom() as first preference when it is available in postgres, or if it is not an easy decision, get some data on what the tradeoffs are

2024-10-01 23:19:21 GMT

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re macos i vaguely believe its syscall overhead isn’t great? which is sort of suggested by the relative performance numbers i got, though the differences in architecture are enough that i can’t make any clear judgments!

2024-10-01 23:14:00 GMT

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thank you for the kind review! i am glad you liked it :-)
re. chacha8, i was intrigued by aumasson’s “too much crypto” — and wow, what an arse tytso can be
thanks for pointing out the aesni vs chacha issue, that will be useful to know if i dig in further
i wonder if vgetrandom will make it easier to experiment with algorithm / performance choices, while keeping the secure rekeying - or is the key schedule too tied up with the choice of algorithm?

2024-10-01 14:30:17 GMT

on my blog!
https://dotat.at/@/2024-10-01-getentropy.html
getentropy() vs RAND_bytes()
in which i get some curious benchmark numbers
and i waffle on at length about getentropy() in case anyone needs a primer on its hows, whys, and wherefores

2024-09-15 20:42:02 GMT

2023 retro-link! https://brailleinstitute.org/freefont - Atkinson hyperlegible font.

2024-09-06 11:42:02 GMT

https://berthub.eu/articles/posts/simple-parallelism-idiom/ - A simple generic parallelism idiom and C++17 specifics.

2024-09-03 01:25:09 GMT

on my blog!
https://dotat.at/@/2024-09-02-ewma.html
exponential rate limiting
a new write-up of the rate limiting algorithm i developed in 2005-2006, shorn of all the email specifics that swamped my old notes from the time

2024-08-12 11:42:02 GMT

2023 retro-link! https://tavianator.com/2023/futex.html - You could have invented futexes.

2024-08-04 08:42:02 GMT

https://viralinstruction.com/posts/mojo/ - A look at the Mojo language for bioinformatics.

2024-07-12 14:42:02 GMT

2022 retro-link! https://db.cs.cmu.edu/mmap-cidr2022/ - Are you sure you want to use mmap() in your database management system?