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[deathshadow]

Still, you're swap32 function should be longword, not word, no?

word and $FFFF0000 === 0 -- ALWAYS
word shl 16 === 0 -- ALWAYS.

So in effect:

result:=(Swap16(x and $ffff) shl 16) or Swap16((x and $ffff0000) shr 16);

is the same thing as saying

result:=0;

Which means on big-endian systems when your swap function is called, you'll get nothing but zero.

Also, you're sending zero to your swap16 function...

function Swap32(x:longword):longword;
begin
 result:=(Swap16(x and $ffff) shl 16) or Swap16(x shr 16);
end;

Is what you should have there. What you have right now won't work... Thankfully it's only called on big endian systems -- and you've probably only tested little endian.

It may also need typecasting forced, since swap16 returns word, not longword meaning that shl 16 could STILL result in zero.