[Dylan16807]

> Because safe code isn't fast enough to decode live video.

I strongly doubt that.

And if any implementation of AV2 can be "fast enough", then there should be no question at all that we can write "fast enough" safe decoders for every other codec. Absolutely no way safe code is inherently that much slower.

[cogman10]

Show me the AV1, H.265, or even H.264 decoder that doesn't ultimately rely heavily on hand written assembly to achieve "fast enough".

You can doubt all you like. Ultimately, there's a reason why dav1d includes hand coded SIMD for common platforms.

It's simply impossible to get a compiler to emit something like this [1].

[1] https://github.com/videolan/dav1d/blob/master/src/x86/ipred_...

[Dylan16807]

Is it simply impossible to get compiled code within a factor of five? That claim needs strong evidence.

More importantly, if you can show that your assembly code isn't altering pointers it shouldn't alter, and isn't going out of bounds on its reads, you're most of the way to having assembly in your verified safe code. And rough bounds checking with padding can as cheap as a bitmask.

[cogman10]

> Is it simply impossible to get compiled code within a factor of five? That claim needs strong evidence.

1. I didn't make that claim.

2. A negative assertion doesn't require evidence. If I say "this is impossible to do" the burden to disprove me is showing it's actually possible. You can't prove a negative. For example, if I say "the tooth fairy doesn't exist" I don't need to provide evidence of the tooth fairy's non-existence. If you disagree, you need to provide evidence to the contrary.

[Dylan16807]

> 1. I didn't make that claim.

Then you didn't read my previous comment correctly. AV2 must be "fast enough" if the designers aren't crazy. And AV2 is 5x slower than AV1. Therefore if compiled code is within a factor of five of hand-written assembly, it's "fast enough" for AV1, and h.264, and probably h.265 too.

You were disagreeing with my claim that other codecs could be "fast enough" with a safe compiler, right? If you weren't disagreeing, I don't know why you challenged me to show you some particular kind of code.

> 2. A negative assertion doesn't require evidence. If I say "this is impossible to do" the burden to disprove me is showing it's actually possible. You can't prove a negative. For example, if I say "the tooth fairy doesn't exist" I don't need to provide evidence of the tooth fairy's non-existence. If you disagree, you need to provide evidence to the contrary.

You're saying it's "simply impossible" for a compiler to optimize instructions to a certain level. But anything one person can code, another person can teach a compiler to do in similar situations. I don't need to show you an example, I just need to point you at the Church-Turing thesis and related documents.