elaborating:
Code:
program test;
begin
  WriteLn(BsfDword(0));
  WriteLn(BsfQWord(0));
  WriteLn({$I %FPCVERSION%});
end.
d:chentrahmodulestests>c:FPC2.6.4bini386-win32fpc bsfdword.pas
Free Pascal Compiler version 2.6.4 [2014/03/06] for i386
Copyright (c) 1993-2014 by Florian Klaempfl and others
Target OS: Win32 for i386
Compiling bsfdword.pas
Linking bsfdword.exe
7 lines compiled, 0.1 sec , 25616 bytes code, 1628 bytes data

d:chentrahmodulestests>bsfdword
0
4231860
2.6.4

d:chentrahmodulestests>c:FPC3.0.4bini386-win32fpc bsfdword.pas
Free Pascal Compiler version 3.0.4 [2017/10/06] for i386
Copyright (c) 1993-2017 by Florian Klaempfl and others
Target OS: Win32 for i386
Compiling bsfdword.pas
Linking bsfdword.exe
7 lines compiled, 0.1 sec, 25424 bytes code, 1252 bytes data

d:chentrahmodulestests>bsfdword
255
255
3.0.4