use Benchmark;

$iterations = 1000000;     

$name1 = "Alternation"; 
$code1 = ' $_="ABBA"; s/(A|B)/X/g; ';

$name2 = "Class"; 
$code2 = ' $_="ABBA"; s/[AB]/X/g; ';

$name3 = "Substitution"; 
$code3 = ' $_="ABBA"; s/A/X/g; ';

$name4 = "Transliterate"; 
$code4 = ' $_="ABBA"; tr/A/X/; ';

timethese($iterations, {$name1 => $code1, 
						$name2 => $code2,
						$name3 => $code3,
						$name4 => $code4,
						} );

__END__

C:\>perl test.pl

Benchmark: timing 1000000 iterations of Alternation, Class, Substitution, Transliterate...

Alternation:   36 wallclock secs (35.92 usr +  0.00 sys = 35.92 CPU) @ 27839.64/s  (n=1000000)
     Class:    23 wallclock secs (23.12 usr +  0.00 sys = 23.12 CPU) @ 43252.60/s  (n=1000000)
Substitution:  20 wallclock secs (20.81 usr +  0.00 sys = 20.81 CPU) @ 48053.82/s  (n=1000000)
Transliterate:  8 wallclock secs ( 8.07 usr +  0.00 sys =  8.07 CPU) @ 123915.74/s (n=1000000)

C:\>


##</code><code>##

# mine.pl

sub show {
    my @data = @_;
    for (@data) {
        s/\266/%B6/g;
        s/\267/%B7/g;
        tr/ /\267/;
        s/\t/ -> /g;
        s/\n/\266\n/g;
    }
  return wantarray ? @data : join'',@data;
}

@data = (<DATA>)[0..7];
my $start = time;
for (0..100000) { my @new = show(@data) }
printf "Mine takes %d seconds", (time - $start);

__DATA__
	tab
    4 spaces, trailing tab	
	    tab and 4 spaces
		
 -> tab¶
····4·spaces,·trailing·tab -> ¶
 -> ····tab·and·4·spaces¶
 ->  -> ¶
¶


# yours.pl

my %mapping = (
    "\t"   => ' -> ',
    " "    => chr(0267),
    "\n"   => chr(0266)."\n",
    "\266" => '%B6',
    "\267" => '%B7',
	);

my $pattern = qr/([@{[join '', keys %mapping]}])/;

sub show {
    my @data = @_;
    s/$pattern/$mapping{$1}/g for (@data);
    return wantarray ? @data : join'',@data;
}

@data = (<DATA>)[0..7];
my $start = time;
for (0..100000) { my $new = show(@data) }
printf "Yours takes %d seconds", (time - $start);

__DATA__
	tab
    4 spaces, trailing tab	
	    tab and 4 spaces
		
 -> tab¶
····4·spaces,·trailing·tab -> ¶
 -> ····tab·and·4·spaces¶
 ->  -> ¶
¶