← Back to context

Comment by Aurornis

3 days ago

> It doesn’t work like that. If an image processing algorithm takes 2 instructions per pixel, adding a check to every access could 3-4x the cost.

Your understanding of how bounds checking works in modern languages and compilers is not up to date. You're not going to find a situation where bounds checking causes an algorithm to take 3-4X longer.

A lot of people are surprised when the bounds checking in Rust is basically negligible, maybe 5% at most. In many cases if you use iterators you might not see a hit at all.

Then again, if you have an image processing algorithm that is literally reading every single pixel one-by-one to perform a 2-instruction operation and calculating bounds check on every access in the year 2025, you're doing a lot of things very wrong.

> This is why if you dictate bounds checking then the language becomes uncompetitive for certain tasks.

Do you have any examples at all? Or is this just speculation?

6 comments

Aurornis

Reply
monkeyelite  3 days ago

> Your understanding of how bounds checking works in modern languages and compilers is not up to date.

One I am familiar with is Swift - which does exactly this because it’s a library feature of Array.

Which languages will always be able to determine through function calls, indirect addressing, etc whether it needs to bounds check or not?

And how will I know if it succeeded or whether something silently failed?

> if you have an image processing algorithm that is literally reading every single pixel one-by-one to perform a 2-instruction operation and calculating bounds check on every access in the year 2025, you're doing a lot of things very wrong

I agree. And note this is an example of a scenario you can encounter in other forms.

> Do you have any examples at all? Or is this just speculation?

Yes. Java and python are not competitive for graphics and audio processing.

  • Aurornis  2 days ago

    > Yes. Java and python are not competitive for graphics and audio processing.

    Because Python is an interpreted language and Java has garbage collection, not because they have bounds checking.

    Using a language like Rust the bounds checking overhead compared to C code is usually minimal, like 0-5%. The compiler can even optimize away many bounds checks (safely) if you structure your code properly, such as with iterators.

    Here's an example article : https://shnatsel.medium.com/how-to-avoid-bounds-checks-in-ru...

    Make sure you read the note about how the author was mistaken about the 15% speedup from bounds checking. The actual bounds check change was much less, like a couple percent. You can even structure your code so that the bounds check disappears altogether when the compiler can confirm safety at compile time.