in reply to Tail recursion using goto ⊂ (was: Re^3: Trinary Operator Semantics)
in thread Trinary Operator Semantics

Oddly enough, "optimized" tail recursion is significantly slower than recursing the same way without the goto: 
sub faster {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    &faster;
}

[download]
Using this test: 
cmpthese( -10, {
        "normal" => sub { normal(50000) },
        "tail"   => sub {   tail(50000) },
        "faster" => sub { faster(50000) },
    }
);

[download]
I got these results: 
         Rate normal   tail faster
normal 2.34/s     --    -0%   -41%
tail   2.35/s     0%     --   -41%
faster 3.96/s    69%    68%     --

[download]
Caution: Contents may have been coded under pressure.

Replies are listed 'Best First'.
Re^2: Tail recursion using goto ⊂ (was: Re^3: Trinary Operator Semantics)
by demerphq (Chancellor) on May 27, 2005 at 17:59 UTC

    Of course a loop is even faster... 

    #!perl 
use strict;
use Benchmark qw(cmpthese);
my %counter;

sub normal {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    $counter{(caller(0))[3]}++;
    return normal(@_);
}

sub tail {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    $counter{(caller(0))[3]}++;
    goto &tail;
}

sub faster {
    return 0 unless $_[0];
    @_ = ($_[0] - 1);
    $counter{(caller(0))[3]}++;
    &faster;
}

sub loop {
    for (0..$_[0]) { $counter{(caller(0))[3]}++; }
    return 0;
}

cmpthese( -3, {
        "normal" => sub { normal(50000) },
        "tail"   => sub {   tail(50000) },
        "faster" => sub { faster(50000) },
        "loop"   => sub { loop(50000) },
    }
);

__END__
         Rate normal   tail faster   loop
normal 2.15/s     --    -8%   -18%   -38%
tail   2.35/s     9%     --   -11%   -32%
faster 2.64/s    23%    12%     --   -24%
loop   3.45/s    60%    47%    31%     --

    [download]

    I put the caller thingee in there to ensure that the for loop didnt get optimized away. Which is in itself also a good argument for just using a loop in the first place.

    ---
    $world=~s/war/peace/g

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[d/l]
Re^2: Tail recursion using goto ⊂ (was: Re^3: Trinary Operator Semantics)
by Joost (Canon) on May 27, 2005 at 17:21 UTC
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In Section Meditations