What is it about ?

  Free Pascal supports the new MMX (Multi-Media extensions) instructions of Intel processors. The idea of MMX is to process multiple data with one instruction, for example the processor can add simultaneously 4 words. To implement this efficiently, the Pascal language needs to be extended. So Free Pascal allows to add for example two array[0..3] of word, if MMX support is switched on. The operation is done by the MMX unit and allows people without assembler knowledge to take advantage of the MMX extensions.

Here is an example:

uses
   MMX;   { include some predefined data types }

const
   { tmmxword = array[0..3] of word;, declared by unit MMX }
   w1 : tmmxword = (111,123,432,4356);
   w2 : tmmxword = (4213,63456,756,4);

var
   w3 : tmmxword;
   l : longint;

begin
   if is_mmx_cpu then  { is_mmx_cpu is exported from unit mmx }
     begin
{$mmx+}   { turn mmx on }
        w3:=w1+w2;
{$mmx-}
     end
   else
     begin
        for i:=0 to 3 do
          w3[i]:=w1[i]+w2[i];
     end;
end.