[chongli]

In one sense, C is the unsafe code block for myriad other languages, like Python. Python users don’t want to deal with undefined behaviour either. They want to write their high level code in NumPy or PyTorch and just have everything work very fast.

Little do they know: they rely on C for those libraries and for things like ATLAS and LAPACK, which implement the underlying numerical linear algebra code. Well, it turns out that ATLAS relies pretty heavily on optimizing C compilers to generate optimal code on many different platforms. At the bottom of all this are the many loop optimizations included in compilers which, thanks to undefined behaviour in the C spec, are able to assume that code is always on the happy path.

It also turns out that Rust includes bindings to ATLAS and LAPACK. I would imagine at some point people might want to write a new linear algebra package in pure Rust. I think it’ll be quite difficult to match the performance of those two in safe Rust, but we’ll see.

[jamincan]

Isn't LAPACK written in Fortran?

[chongli]

You're right, and ATLAS is as well, but Fortran has undefined behaviour [1] for all the same reasons that C does.

[1] https://stackoverflow.com/a/57558908