C:\test>1039630-b.pl14 -SHOW=0
Looking for 'fredfre' in 'fredfrefredfr'

       tye found 'fredfrefred'; excluded from further consideration


      svc4 found 'redfrefredf'; excluded from further consideration

Looking for 'fredfre' in 'fredfrefredf'
Looking for 'fredfre' in 'fredfrefred'

       hdb found 'none found'; excluded from further consideration

Looking for 'fredfre' in 'fredfrefre'
Looking for 'fredfre' in 'fredfrefr'
Looking for 'fredfre' in 'fredfref'
Looking for 'fredfre' in 'fredfre'
Looking for 'fredfre' in 'fredfrefredfrefredfr'

   choroba found 'fredfrefredfre'; excluded from further consideration

Looking for 'fredfre' in 'fredfrefredfrefredf'
Looking for 'fredfre' in 'fredfrefredfrefred'
Looking for 'fredfre' in 'fredfrefredfrefre'
Looking for 'fredfre' in 'fredfrefredfrefr'
Looking for 'fredfre' in 'fredfrefredfref'
Looking for 'fredfre' in 'fredfrefredfre'

      Eily found 'fredfrefred'; excluded from further consideration

Partisipants in performance tests: anomalous tobyink damianc

##</code><code>##

#! perl -slw
use strict;
use 5.014;
use Time::HiRes qw[ time ];

my %tests = (
    tye => sub {
        state $re = qr[^((.*?).*?)(?=.)\1*\2$];
        my $r = shift;
        $$r =~ $re and return $1;
        return;
    },
    choroba => sub {
        state $re = qr[^((.*).*)\1*\2$];
        my $r = shift;
        $$r =~ $re and return $1;
        return;
    },
    damianc => sub {
        state $re = qr[
            ^(.+?)(?{$^N}) ## $1 as $^R
            (?| \1+$()     ## Exact rep, no $2
              | \1*(.+)$   ## Partial rep as $2
                  ## Check its a proper prefix
                  (??{ $^N eq substr( $^R, 0, length($^N)) ? '' : '(?!)' })
            )
        ]x;
        my $r = shift;
        $$r =~ $re and return $1;
        return;
    },
    tobyink => sub {
        my $input  = shift;
        my $length = length $$input;

        for my $i ( 1 .. $length ) {
            my $possible = substr( $$input, 0, $i );
            my $repeated = $possible x ( 1 + int( $length / $i ) );
            return $possible if $$input eq substr( $repeated, 0, $length );
        }
        return;
    },
    hdb => sub {
        my $input = shift;
        my $length = length $$input;
        my $i = 0;
        my $possible;
        while( 1 ) {
            $possible = substr $$input, 0, $i+1; # increase length by 1
            $i = index $$input, $possible, $i+1; # find next occurence of candidate
            return if $i < 0;            # if not found return full string => no repetition
            $possible = substr $$input, 0, $i;   # this is the minimum length candidate
            return $possible if $$input eq substr( $possible x ( 1 + int( $length / $i ) ), 0, $length ); # success
        }
    },
    Eily => sub {
        my $input = shift;
        local $_ = reverse $$input;
        /^(.*)(.+?\1)\2*$/ and return reverse $2;
        return;
    },
    anomalous => sub {
        state $re = qr[ \A (.+?) \1* (.*) (?(?{ 0 != index $1, $2 }) (*FAIL)) \z ]xms;
        my $r = shift;
        $$r =~ $re and return $1;
        return
    },
    svc4 => sub {
        my $search = shift;
        my $tail_length = 1;
        my $tail_step   = int( length( $$search ) / 2 );

        while ($tail_step > 0) {
            $tail_length += $tail_step
                while substr( $$search, 0, $tail_length + $tail_step )
                eq    substr( $$search, -( $tail_length + $tail_step ), ( $tail_length + $tail_step ) )
            ;
            $tail_step = int( $tail_step / 2 );
        }

        my $body_length = length( $$search ) - $tail_length;
        my $longest = $body_length;
        my $n = $body_length - 1;
        while( $n > 1 ) {
            if( ( $body_length % $n ) == 0 ) {
                if( substr( $$search, 0, $n ) eq substr( $$search, $n, $n ) ) {
                    $longest = $n;
                    last;
                }
            }
            $n--;
        }
        return substr( $$search, 1, $longest );
    },
);

our $SHOW //= 1;

## basic functionality
my $base = 'fredfre';
for my $rep ( 2 .. 3 ) {
    my $full = $base x $rep;
    for my $x ( 1 .. length( $base ) ) {
        my $str = substr( $full, 0, -$x ); ## make partial
        print "Looking for '$base' in '$str'";
        for my $test ( keys %tests ) {
            my $res;
            eval {
                local $SIG{ALRM} = sub { die "timeout" };
                alarm 10;
                $res = $tests{ $test }->( \$str ) // 'none found';
                alarm 0;
            };
            $SHOW and printf "%10s -> %s\n", $test, $res // $@;
            if( $res ne $base and not $base eq $str
            or $@ eq 'timeout'
            ) {
                delete $tests{ $test };
                printf "\n%10s found '%s'; excluded from further consideration\n\n",
                    $test, $res // $@
                ;
            }
        }
    }
}
print "Partisipants in performance tests: @{[ keys %tests ]}";
exit;