Opportunity: Software Execution Time Determinism

[Walter Bright via Digitalmars-d]

On 4/13/2016 5:31 PM, Simen Kjaeraas wrote:
> On Wednesday, 13 April 2016 at 22:58:26 UTC, Walter Bright wrote:
>> The compiler could be fairly easily compute cyclomatic complexity, but how
>> that would be used to determine max time escapes me.
>>
>> For example, how many times would a particular loop be executed? Isn't this
>> the halting problem, i.e. not computable?
>
> The first step is simple - we care only about functions being
> constant-time. Let's invent a @keyword for that: @constanttime.
>
> @constanttime functions can only call other functions marked
> @constanttime, and may not contain conditionals, gotos or
> while-loops.
>
> @constanttime functions may contain for and foreach-loops, iff
> the number of iterations are known at compile-time, and 'break'
> is never used.

Very interesting. Recursion would have to be disallowed as well.


> The part about conditionals seems a bit harsh, but it's got to
> be there for determinism.

Understood.


> Not knowing Nordlöw's use case I can't say for sure what he
> actually needs.

Your ideas are good. Let's see what Nordlöw says.