[fpc-pascal] Common OpenMP syntax?

Steve Williams stevewilliams at kromestudios.com
Thu Jul 20 11:41:25 CEST 2006

Florian Klaempfl wrote:
> I'am currently thinking about implementing OpenMP support in FPC.
> However, there is currently (to my knowledge) no pascal syntax defined
> for OpenMp support. Do you think we can find a common syntax to simplify
> things for users? I've some ideas how it be done, but I want to hear
> other ideas first so they are maybe better if they aren't influenced by
> my ideas :)
> I started also a wiki page about it
> http://www.freepascal.org/wiki/index.php/OpenMP_support where ideas can
> be written down and shared.

I would suggest something along the lines of the C/C++ implementation, 
but using the Pascal form of compiler directives.

Using some of the documented examples in the v2.5 spec:

Example A.1.1:
procedure a1(n: Integer; a: PSingleArray; b: PSingleArray);
  i: Integer;
  {$omp parallel for}
  for i := 1 to n - 1 do
    b^[i] := (a^[i] + a^[i - 1]) / 2.0;

Example A.5.1:
uses omp;

  {$omp parallel num_threads(10)}
    (* Do work here *)

Example A.13.1:

function dequeue(var a: Single): Integer;
procedure work(i: Integer; var a: Single);


procedure a13(var x: Single; var y: Single);
  ix_next, iy_next: Integer;
  {$omp parallel shared(x, y) private(ix_next, iy_next)}
    {$omp critical (xaxis)}
      ix_next := dequeue(x);
    work(ix_next, x);

    {$omp critical (yaxis)}
      iy_next := dequeue(y);
    work(iy_next, y);


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