Benchmark: timing 15000 iterations of his, mine, mine-less-lgnt, other
+...
       his:  5 wallclock secs ( 4.94 usr +  0.00 sys =  4.94 CPU) @ 30
+36.44/s (n=15000)
      mine:  5 wallclock secs ( 4.94 usr +  0.01 sys =  4.95 CPU) @ 30
+30.30/s (n=15000)
mine-less-lgnt:  3 wallclock secs ( 3.43 usr +  0.00 sys =  3.43 CPU) 
+@ 4373.18/s (n=15000)
     other: 22 wallclock secs (20.89 usr +  0.03 sys = 20.92 CPU) @ 71
+7.02/s (n=15000)
[download]

UpdateThis version is competely wrong!! It is quick because it does nothing at all. I benchmarked this, but verified the output of a completely different, correct, but much slower piece of code.

A subtle variation on my last version acheives a worthwhile speedup. It's about 50% quicker than my previous best and over twice as fast as the original.

I wish there was a way to put a big red cross through the code as well.

## !!! DO NOT USE !!! TOTALLY BOGUS CODE. !!!
sub peel2 {
    my( $s, $n ) = @_;
    my($start, $stop, $p, $q) = (length $s, 0, 0);
    ($start, $stop) = ($p, $q)
        while $p =  1+index( $s, ')', $stop  ) < 0
          and $q =   rindex( $s, '(', $start ) < 0
          and $n--;
    substr $s, $start, $stop - $start;
}

                 Rate            his mine-less-lgnt           buk2    
+      buk3
his             569/s             --           -35%           -45%    
+      -62%
mine-less-lgnt  875/s            54%             --           -15%    
+      -42%
buk2           1026/s            80%            17%             --    
+      -32%
buk3           1502/s           164%            72%            46%    
+        --
[download]

---

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller

As my original attempt was so crap, I thought I'd take another crack. Abandoning any attempt at validation and avoiding the regex engine completely, I came up with this which seems to be about 15% better than the best so far.

sub peel {
    my( $s, $n ) = @_;
    my( $start, $stop ) = ( 0, length $s );
    ($start,$stop) = (
        1 + index( $s, '(', $start   ),
           rindex( $s, ')', $stop -1 )

      # reformatting_for_posting error corrected
# Was    ) while $n-- > 0 and index( $s, '(', $start +1 ) > 0;

    ) while $n--    and index( $s, '(', $start +1 ) > 0;
    substr $s, $start, $stop - $start;
}
                 Rate mine-less-lgnt           buk2
mine-less-lgnt  918/s             --           -15%
buk2           1075/s            17%             --
[download]

---

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller

Not bad, but pluggiing it into Aristotle's magic machine (at here) yields:

not ok 8 - by substr for case -1
#     Failed test (./t53.pl at line 90)
#          got: 'hello(what(is(this(all(about)))))'
#     expected: 'about'
[download]

It's easy to be fast when you don't cover all the cases. ;-P

--Bob Niederman, http://bob-n.com

Oh well, worth a try:)

---

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller