#!/usr/bin/perl -w

use Benchmark qw(cmpthese);
$s = "\bthis is an\b correct\b\b\b usage\b";

sub uk {
  $a = $s;
  $a =~ s[(?:[^\cH]\cH|^\cH)][]g while 1+index $a, chr(8);
  $a;
}

sub new1 {
  $a = $s;
  while ($a =~ s/(?:[^\cH]\cH|^\cH+)//g) {}
  $a;
}

sub smack {
  $a = $s;
  do 1 while ($a =~ s/(?:[^\cH]\cH|^\cH+)//g);
  $a;
}

cmpthese(-5,{uk=>\&uk,new1=>\&new1,smack=>\&smack});
$s x= 100;
cmpthese(-5,{uk=>\&uk,new1=>\&new1,smack=>\&smack});

__END__
Benchmark: running new1, smack, uk for at least 5 CPU seconds...
      new1:  5 wallclock secs ( 5.23 usr +  0.00 sys =  5.23 CPU) @ 31024.33/s (n=162393)
     smack:  6 wallclock secs ( 2.16 usr +  3.05 sys =  5.22 CPU) @ 2916.79/s (n=15222)
        uk:  5 wallclock secs ( 5.19 usr +  0.00 sys =  5.19 CPU) @ 36570.60/s (n=189710)
         Rate smack  new1    uk
smack  2917/s    --  -91%  -92%
new1  31024/s  964%    --  -15%
uk    36571/s 1154%   18%    --
Benchmark: running new1, smack, uk for at least 5 CPU seconds...
      new1:  6 wallclock secs ( 5.48 usr +  0.00 sys =  5.48 CPU) @ 368.11/s (n=2016)
     smack:  6 wallclock secs ( 5.01 usr +  0.41 sys =  5.41 CPU) @ 326.56/s (n=1768)
        uk:  5 wallclock secs ( 5.23 usr +  0.00 sys =  5.23 CPU) @ 462.14/s (n=2419)
       Rate smack  new1    uk
smack 327/s    --  -11%  -29%
new1  368/s   13%    --  -20%
uk    462/s   42%   26%    --