UUID
ChessPositionRanking
| UUID | ChessPositionRanking | |
|---|---|---|
| 9 | 29 | |
| 12,338 | 132 | |
| - | - | |
| 7.8 | 2.5 | |
| 5 days ago | 5 months ago | |
| PHP | Haskell | |
| MIT License | MIT License |
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UUID
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Weekly help thread
I'd recommend using either Ramsey/uuid or generating a random number using random_bytes(32) then compressing it. 32 bits of randomness should be sufficient for most programs.
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eli5 With billions and billions of people over time, how can fingerprints be unique to each person. With the small amount of space, wouldn’t they eventually have to repeat the pattern?
Of course, theoretical math and applied math often work out differently. Here's a thread with a guy claiming his team's software is running into "Several hundred [UUID] collisions per day"
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weird php results microtime/hrtime
Or just use a library.
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UUIDs are a wonderful invention
I'll leave this here https://github.com/ramsey/uuid/issues/80
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What are types of bugs that only show up after thousands or millions of times of the code being run.
Not really in the realm of “thousands” of runs, but UUID collisions are possible and have been observed multiple times after only 1 million generations due to unknown reasons.
- Generating unique key code using PHP
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Sortable Collision-Free UUIDs
There's also the risk of bad randomness sources and/or bugs.
One popular UUID library got a bug report stating: "We are generating about 1M UUID4 a day, and we are getting several hundred collisions a day". And so they were; turned out to be a bug/weird interaction between the OpenSSL library they were using for randomness and forking. (Details here, although it was all fixed years ago of course: https://github.com/ramsey/uuid/issues/80)
On paper, you should never, ever, ever see a collision when generating a mere million v4 UUIDs a day, much less hundreds of collisions. But that doesn't mean it can't happen!
This is also an interesting bit of analysis; comes from a company that processed a lot of UUIDs generated in browsers, checked, and discovered about 5 collisions per million UUIDs. Again, not what you'd naively expect! (Turned out to be mostly driven by misbehaving crawlers.) https://medium.com/teads-engineering/generating-uuids-at-sca...
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Things You Should Do Now
just make sure you have everything configured correctly on your system if using UUIDs:
https://github.com/ramsey/uuid/issues/80
In the types of systems that need UUIDs there is probably no easy way to check for collisions. The prospect of mystery data corruption with no ability to trace it down frightens the hell out of me.
The only reason that issue was reported is because someone was actually doing the collision checking. That's not going to be the norm in UUID systems. Think about it.
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A UUID can have so many combinations that UUIDs are effectively unique. But it's possible to generate the same one twice, however small the chance. Is it best practice to take this chance into account, checking to be sure you haven't used it?
In theory the risk of collision is so small it can be written off, but implementations can have bugs.
ChessPositionRanking
- Chess Position Ranking
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How to Store a Chess Game in 26 Bytes Using Bit-Level Magic
3. There's extra nuanced things you might want to handle in the coding, like that pawns can't be on their own back row. That is significantly harder.
It looks to me like https://github.com/tromp/ChessPositionRanking has resolved these sorts of issues, but I haven't dug into exactly how.
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Permutation Iteration and Random Access
Multinomial rankings can be combined with a dozen others to rank a subset of all chess positions including all legal ones. This allows one to sample millions of random such positions, determine how many are legal, and thus obtain an accurate estimate of 4.8&10^44 legal chess positions [2].
[1] https://github.com/tromp/ChessPositionRanking/blob/main/src/...
[2] https://github.com/tromp/ChessPositionRanking
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The number of legal Chess diagrams is less than 4 × 10^37 which is an improvement on the previous upper bound of 2 × 10^40 by Steinerberger.
The key words being "without promotion". Both bounds, this one and Steinerberger's, only consider positions reachable without promotion. Allowing promotions, one estimate suggests that the number is close to 4.82 × 10^44.
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eli5 With billions and billions of people over time, how can fingerprints be unique to each person. With the small amount of space, wouldn’t they eventually have to repeat the pattern?
source
- Accurately estimating the number of legal chess positions
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"Chess too simple for my big brain, not like mobile strategy game"
This one as well as Shannon number wiki seem to say that possible sensible moves are about 10^40 while and 10^120 while taking any moves (maybe including some illogical / illegal ones) .
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How to build a Chess Engine, an interactive guide
Shannon's estimate was based on very primitive methods; by generating random positions and using fairly advanced methods to see whether they are legal or not (ie., can you construct a proof game for it, or prove that it could never happen), you will get much closer. A group of people have been working on this, and their current best estimate is (4.822 +- 0.028) * 10^44, or a bit over 148 bits. (Amazingly enough, Shannon wasn't all that far off on this account! His estimated number of legal games seems much more dodgy, though.)
http://talkchess.com/forum3/viewtopic.php?f=7&t=77685&sid=e3...
Practically speaking, https://github.com/tromp/ChessPositionRanking gives a number between 0 and approx. 8.7 * 10^45 for any legal position, so it's only a couple of bits away from optimality.
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Ask HN: Teach Me Something New
The number of chess positions has now been estimated with 2 digits of accuracy as ~ 4.8 x 10^44: https://github.com/tromp/ChessPositionRanking
What are some alternatives?
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