#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

my $stretch = 10;
my $mismatches = 1;

substr $reference_str, 0, 0, 'x' x (length($small_str) - 1);
$reference_str .= 'x' x (length($small_str) - 1);

for my $start_pos (0 .. length($reference_str) - length($small_str)) {
    my $substr = substr $reference_str, $start_pos, length($small_str);

    my ($from, $diffs) = (0, 0);
    for my $inner_pos (0 .. length($small_str) ) {
        ++$diffs if substr($substr, $inner_pos, 1)
                 ne substr $small_str, $inner_pos, 1;

        if ($diffs > $mismatches || $inner_pos == length($small_str) ) {
            say join "\n\t",
                $start_pos + $from + 1 - length $small_str,
                substr($small_str, $from, $inner_pos - $from),
                substr($reference_str, $from + $start_pos, $inner_pos - $from)
                if $inner_pos - $from >= $stretch;

            ++$from until (substr $small_str, $from, 1) ne substr($substr, $from, 1) || $from > $inner_pos;
            ++$from;
            --$diffs;
        }
    }
}


##</code><code>##

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,