[TUHS] I can't drive 55: "GOTO considered harmful" 55th anniversary

[Steffen Nurpmeso]

Dave Horsfall wrote in
 <alpine.BSF.2.21.9999.2303101657460.4881 at aneurin.horsfall.org>:
 |On Thu, 9 Mar 2023, Warner Losh wrote:
 |> In C I use it all the time to do goto err for common error recovery 
 |> because C doesn't have anything better.
 |
 |<AOL>
 |Me too :-)
 |</AOL>
 |
 |Seriously, I also use setjmp()/longjmp() for a more elegant exit from a 

That is sheer unbelievable, really?  _So_ expensive!

 |deeply-nested loop; "break N" to break out of "N" loops, anyone?  I 
 |haven't found that yet...

Very often i find myself needing a restart necessity, so "continue
N" would that be.  Then again when "N" is a number instead of
a label this is a (let alone maintainance) mess but for shortest
code paths.

All the "replacements", like closures, plain inner functions, even
more contorted conditionals (i think in the last seven days i saw
at least three fixes fly by due to logic errors in contorted
conditionals, tiny C compiler, OpenBSD i think bpf/bgpd?, and some
FreeBSD commit, which sums up as "Pascal: no"), and "state machine
indicating variables" are not as elegant and cheap, and do not
allow an as human-receivable control flow (imho), as a simple
jump can be.  Like my always quoted exampe that adds unnecessary
conditionals which evaluate over and over again for nothing

                if(defined($nl = $self->begin_line)){
                        $self->begin_line(undef);
                        $self->seen_endl(1);
                        $ogoditisanewperl = 1 #goto jumpin;
                }

                while($ogoditisanewperl || ($nl = readline $self->infh)){
                        if(!$ogoditisanewperl){
                                ++${$self->__lineno};
                                $self->seen_endl($nl =~ s/(.*?)\s+$/$1/)
                        }
                        $ogoditisanewperl = 0; #jumpin:

 |Of course, in those days it was setexit() etc :-)

  ENTRY(setexit, 0)
          movab   setsav,r0
          movq    r6,(r0)+
          movq    r8,(r0)+
          movq    r10,(r0)+
          movq    8(fp),(r0)+             # ap, fp
          movab   4(ap),(r0)+             # sp
          movl    16(fp),(r0)             # pc
          clrl    r0
          ret
  ENTRY(reset, 0)
          movl    4(ap),r0        # returned value
          movab   setsav,r1
          movq    (r1)+,r6
          movq    (r1)+,r8
          movq    (r1)+,r10
          movq    (r1)+,r12
          movl    (r1)+,sp
          jmp     *(r1)
  setsav: .space  10*4
          .text

Cheap it is not.  But maybe cheaper than calling a closure or
inner function with all the (repeated) stack setup and unwinding.

 |-- Dave
 --End of <alpine.BSF.2.21.9999.2303101657460.4881 at aneurin.horsfall.org>

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)