10 Mar
2023
10 Mar
'23
5:55 p.m.
Dave Horsfall wrote in
<alpine.BSF.2.21.9999.2303101657460.4881(a)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(a)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)