[fpc-pascal] Strange swap function, what does it do?

[Bo Berglund]

I am working on the conversion of a service application from
Windows/Delphi to Linux/FPC.

When going through the code I found this procedure, which I do not
quite understand the workings of, can someone please explain how it
operates?

procedure Swap2(var Source);
var
  H, L: word;
begin
  H := Hi(word(Source));
  L := Lo(word(Source));
  word(Source) := (L * 256) + H;
end;

It is used in the code like this where Hd is a record and numSteps is
a word sized field:

Swap2(Hd.numSteps);

In other places when word sized variables need to be swapped
(Little/Big-endian conversions) it is done like this instead where
CmdProgNum is a smallint value and the built-in swap function is used:

FR.CmdProgNum := Swap(FR.CmdProgNum);

So the code uses a mix of these and I do not understand what the
strange looking function does...


-- 
Bo Berglund
Developer in Sweden