[ncmncm]

Making a system Turing-complete, even accidentally, does not make it proof against analysis. A system or input for the system may be built out of parts that could be used to make an undecidable system. But that does not mean you can only build undecidable systems with those parts.

It is in fact extremely common to build wholly deterministic machines out of the same parts as our unreliable computers, that are correct by construction. And they may implement a Turing-complete language and still be wholly deterministic, just by limiting the input to what can be proven deterministic in a strictly limited time. Again, this is normally by construction, where the proof is always trivial.

Such a proven-correct system can model literally any space-constrained algorithm.

[mkleczek]

> It is in fact extremely common to build wholly deterministic machines out of the same parts as our unreliable computers, that are correct by construction.

It is neither common nor easy but actually provably impossible. Please read this piece carefully: https://pron.github.io/posts/correctness-and-complexity

[ncmncm]

Yet, it is done, thousands of times every day, all over the world.

You must be misunderstanding the work if you believe that what is being done routinely is impossible.

[mkleczek]

> You must be misunderstanding the work if you believe that what is being done routinely is impossible.

Quite possibly I don't understand what you mean by "work". If by "work" you mean creating provably correct software then no, it is not done routinely.

[ncmncm]

The work is the paper you cited.

People create wholly deterministic state machines all the damn time.

[mkleczek]

> People create wholly deterministic state machines all the damn time.

What do you mean by "wholly deterministic"?

[ncmncm]

All possible states are well-understood, all possible paths through states are mapped.

You can buy an 8-bit adder/accumulator from a catalog.