Opportunity: Software Execution Time Determinism

[Andrei Alexandrescu via Digitalmars-d]

On 4/13/16 6:58 PM, 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?
>
> Andrei has done some great work on determining big O complexity, but
> that's only a small part of this problem.
>
> I don't know about any work in this area, but I can see it would be
> valuable.

Tarjan was among the first to study the problem: 
http://www.cs.princeton.edu/courses/archive/spr06/cos423/Handouts/Amortized.pdf. 
He assigned "computational credits" to functions and designed a type 
system in which functions cannot consume more credits than assigned.

One simpler thing we can do is add an attribute:

void fun() @credits(2);

meaning fun() consumes two computational credits. Then a function that 
calls fun() n times consumes n*2 credits etc. Generally we wouldn't aim 
for automatically determining credits consumed, but we can define a 
library that allows the user to declare credits appropriately.


Andrei