…this is not very efficient in Perl…
You may refer to some disappointing benchmark as this:
Rate goto_recur recursive tail_recur looping
goto_recur 3437/s -- -59% -60% -90%
recursive 8472/s 147% -- -1% -76%
tail_recur 8569/s 149% 1% -- -76%
looping 35417/s 931% 318% 313% --
where the benchmark is that of swampyankee above, adding ikegami's tail_recur and a derived version of that using your goto recipe:
sub _goto_recur {
my ($x, $y) = @_;
if ($x <= 1) {
return $y;
} else {
@_ = ($x - 1, $x * $y);
goto &_goto_recur;
}
}
sub goto_recur {
my ($x) = @_;
return _goto_recur($x, 1);
}
Then I was surprised that throwing out all lexicals and directly
messing with
@_ yields more pleasing results:
sub _goto_recur {
if ($_[0] <= 1) {
return $_[1];
} else {
$_[1] *= $_[0];
--$_[0];
goto &_goto_recur;
}
}
sub goto_recur {
my ($x, $y) = (shift, 1);
# We can't plug the constant 1 directly into $_[1]
# since we want to change that (alias!)
return _goto_recur($x, $y);
}
Gives on my machine:
Rate recursive tail_recur goto_recur looping
recursive 8456/s -- -1% -9% -77%
tail_recur 8519/s 1% -- -8% -76%
goto_recur 9278/s 10% 9% -- -74%
looping 36011/s 326% 323% 288% --
Of course that code does not look very desirable from a maintainers point of view.
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