I don't think 25x speed difference can be attributed to safe code. In most cases safe code just means extra bounds checking or refcounting here and there, which aren't that bad even in hot loops.
The fragment of code in the article with `get_unchecked_mut()` shouldn't be necessary. It's a simple case that LLVM should be able to optimize. And if it didn't, it could be helped by either iterating both slices with `zip()` or a trick `let slice = &slice[0..len];` which proves to LLVM that you have the required length and it doesn't need to be checked again.
But overall the article seems in line what you'd expect from Rust: you have low-level control over memory layout and safety checks, and you can make trade-offs to squeeze maximum performance out of an algorithm if you need to.
The fragment of code in the article with `get_unchecked_mut()` shouldn't be necessary. It's a simple case that LLVM should be able to optimize. And if it didn't, it could be helped by either iterating both slices with `zip()` or a trick `let slice = &slice[0..len];` which proves to LLVM that you have the required length and it doesn't need to be checked again.
But overall the article seems in line what you'd expect from Rust: you have low-level control over memory layout and safety checks, and you can make trade-offs to squeeze maximum performance out of an algorithm if you need to.