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Re: Tail recursion using goto ⊂ (was: Re^3: Trinary Operator Semantics)

by Roy Johnson (Monsignor)
on May 27, 2005 at 17:07 UTC ( #461155=note: print w/replies, xml ) Need Help??


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

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% --

    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

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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