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Math.Pow(-1, 2) == -1 in Windows 11 Insider build

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“Both Math.Pow and std::pow invokes the pow function in UCRT, which is shipped with Windows. The issue should be reported to MSVC instead”

It’s not the job of a bug reporter to figure that out and to verify that nothing goes wrong in setting up stuff for invoking that function or in getting its output back into the C# world.

That’s even more true because the dynamic nature of .NET code makes it far from easy to verify by inspection that that function is just calling the pow function in UCRT. The C# compiler might do constant folding wrong and there might be several ways in which the runtime compiles the CLR code (fast compilation to start running it quickly, slower compilation that produces faster code later if it turns out to be called a lot, etc)

3 days agoby Someone

> If you need to contact us better, joining the osu! Discord server would be best

I really dislike how Discord is slowly eating up the web and being used as the primary channel for communication, when most of the community resources resides in their Discord, it makes it hard for me to find relevant information through the web thanks to Discords lock-in

3 days agoby Alifatisk

I've heard people moan that software is getting exponentially worse. Maybe they're right after all /joke

3 days agoby debo_

I'm surprised that an optimizing compiler lets this case even hit the general `pow` runtime function. I'd have expected it to replace this call by `x * x` so it doesn't hit the expensive general `pow` function.

I find it strange as well that no unit test caught this. Squaring a negative number is definitely a case I'd expect to be covered. Perhaps compiler optimization made this case work in the unit test, allowing the runtime function to break? And then it broken in .net where the JIT compiler is dumber than the C++ compiler?

3 days agoby CodesInChaos

I really want to know how this could have passed CI testing.

(Comments blame it on UCRT, not .NET but… that doesn’t matter much to me.)

3 days agoby fn-mote

Side note.

One of the advantages of using proprietary packaged software is supposed to be a unified support and product.

In this case the maintainer redirects the issue to some other team and passes the ball as if it were an open source project with 50 dependencies with thin responsibilities "no, if there's an issue with a button, you should report it to GUI-button, we do GUI-form and we just pass the button generation to their library"

3 days agoby TZubiri

Off by 2, not so bad

3 days agoby smidgeon

Looks like complex numbers are much simplified on Windows 11.

3 days agoby nkrisc

How did this happen? This feels like the easiest function in the world to write a unit test for?

3 days agoby AlienRobot

How does the OS still function with a basic bug like this?

3 days agoby comrade1234

No idea why this happened. Perhaps Math.Pow(x,y) was implemented as 2**(y*log2(x)) without writing special code to deal with the case where x is negative real and y is integer?

3 days agoby The_suffocated

Should we be surprised that Microsoft doesn't know maths? Was the code for that generated by an LLM?

3 days agoby tempodox

Anyone got a link to the actual OS bug that caused this? I would love to see an explanation of how it happened and what the code looked like.

2 days agoby shthed

30% of all code by Microsoft is written by AIs:

https://techcrunch.com/2025/04/29/microsoft-ceo-says-up-to-3...

So that is the result.

2 days agoby amai

From the response it is already fixed; no details on cause unfortunately: “This uCRT bug has been already reported through another channel a week ago and it got fixed since (OS #58189958: pow(-1, 2) returns -1). It might take a while to be available in the public insider builds”

3 days agoby jasonthorsness

This happens in both C# and C++ according to the report, but what's the link between OS and compiler here?

As far as I remember from days when I used Windows, the version of your visual studio (which has the compiler and standard libraries) was not related to the build of your operating system

3 days agoby Aardwolf

Reminds me of this 2005 paper: https://www.sciencedirect.com/science/article/abs/pii/S01679...

3 days agoby Qem

From the most recent issue comment: “This uCRT bug has been already reported through another channel a week ago and it got fixed since (OS #58189958: pow(-1, 2) returns -1). It might take a while to be available in the public insider builds”.

3 days agoby layer8

Since this seems to be in ucrt and hence a much more widespread problem, it would be nice to know the CRT/Windows versions affected

3 days agoby on_the_train

The good thing is, if (-1)^2=-1, we can prove anything! NP=P, every program halts, axiom of choice - math just becomes so much easier.

3 days agoby waldrews

TIL osu is open source

3 days agoby haunter

So they are vibecoding MSVC now?

Sweet.

2 days agoby gloosx