Stack Space & Ackermann

[rikki cattermole via Digitalmars-d-learn]

On 05/01/2017 7:03 PM, Era Scarecrow wrote:
> On Thursday, 5 January 2017 at 04:53:23 UTC, rikki cattermole wrote:
>> Well, you could create a fiber[0].
>>
>> Fibers allow you to set the stack size at runtime.
>>
>> [0] http://dlang.org/phobos/core_thread.html#.Fiber.this
>
>  Well that certainly does seem to do the trick. Unfortunately I didn't
> get the next output because I ran out of memory to allocate/reallocate
> over 2Gb :P
>
>  I suppose with a 64bit compiling the program might run a bit longer and
> succeed further (with 24Gigs of ram), however the sheer amount of memory
> required will make this little exercise more or less a waste of time.
>
>  Still that was an interesting way around the (stackframe) problem, one
> I'll keep I mind (should i need it again).
>
> void m() {
>     foreach(i; iota(6))
>         foreach(j; iota(6)) {
>             writefln("Ackerman (%d,%d) is : %d", i,j,ack(i,j));
>     }
> }
>
> int main(string[] args) {
>     Fiber composed = new Fiber(&m, 2<<28); //512MB
>     composed.call();
>
>     return 0;
> }
>
> results:
>
> Ackerman (3,5) is : 253
> Ackerman (4,0) is : 13
> Ackerman (4,1) is : 65533
>
> core.exception.OutOfMemoryError at src\core\exception.d(693): Memory
> allocation failed
>

You're using more memory then need to:

foreach(i; 0 .. 6)

No need for iota.