[fpc-devel] Fix for SwapEndian

[Joost van der Sluis]

Hi all,

I've a problem with BeToN with smallints on a x86 system. When you use
BeToN on smallint's with values like $8000 and $8200 it will return
values like $FF80 and $FF82, instead or $0080 and $0082 respectively.
The patch below fixes this, but I'm not sure if it's a correct fix, or
that it's a bug in the compiler. (ie: is this behaviour of shr/shl
normal on signed smallints?)

If this patch is correct, how about the other signed integer-types?

Patch:

--- rtl/inc/generic.inc (revision 10836)
+++ rtl/inc/generic.inc (working copy)
@@ -1707,7 +1707,7 @@
 {$ifndef FPC_SYSTEM_HAS_SWAPENDIAN}
 function SwapEndian(const AValue: SmallInt): SmallInt;
   begin
-    Result := (AValue shr 8) or (AValue shl 8);
+    Result := (word(AValue) shr 8) or (word(AValue) shl 8);
   end;


test-program:

program swap;

uses sysutils;

var si1,si2 : smallint;

begin
  si1 := $8000;
  si2 := $0080;
  si1 := beton(si1);
  if si1<>si2 then
    begin
    writeln('Not good:');
    writeln(IntToHex(si1,2),' should be ', IntToHex(si2,2));
    end;
end.