SLONG API_ROUTINE gds__vax_integer(const UCHAR* ptr, SSHORT length)
{
	if (!ptr || length <= 0 || length > 4)
		return 0;

	SLONG value = 0;
	int shift = 0;

	while (--length > 0)
	{
		value += ((SLONG) *ptr++) << shift;
		shift += 8;
	}

	value += ((SLONG)(SCHAR) *ptr) << shift;

	return value;
}

function gds__vax_integer(ptr: PChar; length: Smallint): Longint;
var
  value: Longint;
  shift: Integer;
begin
  Result := 0;
  if (ptr = nil) or (length <= 0) or (length > 4) then
    Exit;

  value := 0;
  shift := 0;

  while PreDec(length) > 0 do
    begin
      value := value + (Longint(PostInc(ptr)^) shl shift);
      shift := shift + 8;
    end;

  value := value + (Longint(Shortint(ptr^)) shl shift);
  Result := value;
end;

0000000000000000 = 00  (length 1)
0000000000000001 = 01  (length 1)
ffffffffffffffff = ff  (length 1)
000000000000007f = 7f  (length 1)
ffffffffffffff7f = 7f ff  (length 2)
0000000000000080 = 80 00  (length 2)
fffffffffffffed5 = d5 fe  (length 2)
0000000012345678 = 78 56 34 12  (length 4)

procedure Test_vax_integer;

  function DumpBuff(S: string): string;
  var
    i: Integer;
  begin
    Result := '';
    for i := 1 to Length(S) do
      if Result = '' then
        Result := Result + IntToHex(Ord(S[i]), 2)
      else
        Result := Result + ' ' + IntToHex(Ord(S[i]), 2);
  end;

  procedure DoTest(S: string);
  var
    Res: Integer;
    HexSrc: string;
    HexRes: string;
  begin
    HexSrc := DumpBuff(S);
    Res := gds__vax_integer(@S[1], Length(S));
    HexRes := IntToHex(Res, 8);
    Writeln(format('%s = %s (length %d)', [HexRes, HexSrc, Length(S)]));
  end;

begin
  DoTest(#0);
  DoTest(#1);
  DoTest(#$FF);
  DoTest(#$7F);
  DoTest(#$7F#$FF);
  DoTest(#$80#$00);
  DoTest(#$D5#$FE);
  DoTest(#$78#$56#$34#$12);
end;