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0 pointsnextaccountic3y ago0 comments

There is if the algorithm contains race conditions that cause non-deterministic output. The submitted article goes above and beyond to guarantee that the code always output the same answer even though it has race conditions. But that's sometimes not possible or, if it's possible, it's too much of a hassle so it's rarely done.

For example, this project https://github.com/EmbarkStudios/texture-synthesis generates textures and if you run the same code with the same input various times, the results will be slightly different. Here https://github.com/EmbarkStudios/texture-synthesis#notes it says: "When using multiple threads for generation, the output image is not guaranteed to be deterministic with the same inputs. To have 100% determinism, you must use a thread count of one"

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mgaunard3y ago

I gave conditions upon which testing for equality is correct.

Of course if the result is non-deterministic it doesn't satisfy those conditions.

nextaccounticOP3y ago

Unfortunately it may be quite hard to certify that your program qualifies, specially if it's a high performance program that can't be single threaded. An innocuous-looking commit can completely undermine this property.

Doubly so if you must guarantee determinism across multiple platforms! IEEE 754-2008 helps but it defines cross-platform determinism for just a subset of operations. Compilers can also sometimes botch your FP code (there's a number of gotchas - for example, if any library anywhere in your program uses -ffast-math, it may infect the whole program https://stackoverflow.com/questions/68938175/what-happens-if...)

mgaunard3y ago

Achieving exact or correctly-rounded results is much more work than that.

You can look at the crlibm papers for example.

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0 pointsnextaccountic3y ago0 comments

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mgaunard3y ago

I gave conditions upon which testing for equality is correct.

Of course if the result is non-deterministic it doesn't satisfy those conditions.

nextaccounticOP3y ago

mgaunard3y ago

Achieving exact or correctly-rounded results is much more work than that.

You can look at the crlibm papers for example.

j / k navigate · click thread line to collapse