TInterlocked.BitTestAndSet strangeness

[M.Joos 30]

Hi all, when running the following code

program Project105;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils, System.SyncObjs;
var
  Sync: Integer;
  Test: Boolean;

begin
  try
    TInterlocked.BitTestAndClear(Sync,0);
    Test := TInterlocked.BitTestAndSet(Sync,0);
    if Test then
      writeln('Why is Test true here ??') else
      writeln('Okay, That''s what I expected');
    readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Why is it that the variable Test is set to true, when the documentation says  ".... The method returns True if the bit is 1, False otherwise ". Clearly I have set the bit to 0 with TInterlocked.BitTestandClear, haven't I ? What am I missing.

Tested with Delphi 10.1 Berlin.

Edited December 6, 2019 by M.Joos

[Uwe Raabe 2057]

Works as expected in Rio...

[M.Joos 30]

1 hour ago, Uwe Raabe said:

Works as expected in Rio...

You are right, Uwe. Tested it in 10.3.2 and it works as expected.

Upon closer inspection it seems they fixed the Tinterlocked code which in Berlin looked like this:

$ELSEIF Defined(X86ASM)}
asm
  AND   EDX,31
  LOCK BTS   [EAX],EDX
  SETNC  AL
end;
{$ELSE}
var

and in Rio looks like this:

{$ELSEIF Defined(X86ASM)}
asm
  AND   EDX,31
  LOCK BTS   [EAX],EDX
  SETC  AL
end;
{$ELSE}

Okay, and I thought I would be crazy or something

[Alain Weber 0]

Try

  Sync := $FFFFFFFF;
  TInterlocked.BitTestAndClear(Sync, 1);