Using Bit::Vector.
use Modern::Perl;
use Bit::Vector;
use Data::Dump qw/dump/;

my %conversion = (
    ' ' => 0,
    0   => 1,
    1   => 2,
    2   => 3,
    3   => 4,
    4   => 5,
    5   => 6,
    6   => 7,
    7   => 8,
    8   => 9,
    9   => 10,
    A   => 11,
    B   => 12,
    C   => 13,
    D   => 14,
    E   => 15,
    F   => 16,
    G   => 17,
    H   => 18,
    I   => 19,
    J   => 20,
    K   => 21,
    L   => 22,
    M   => 23,
    N   => 24,
    O   => 25,
    P   => 26,
    Q   => 27,
    R   => 28,
    S   => 29,
    T   => 30,
    U   => 31,
    V   => 32,
    W   => 33,
    X   => 34,
    Y   => 35,
    Z   => 36,
);
my %inverted;

my $vector = Bit::Vector->new(6);
for ( keys %conversion ) {
    $vector->from_Dec( $conversion{$_} );
    $conversion{$_} = $vector->to_Bin();
    $inverted{ $vector->to_Bin() } = $_;
}
while (<DATA>) {
    chomp;
    my $string = join '', map { $conversion{$_} } split //;
    my $vector = Bit::Vector->new_Bin( 36, $string );
    my $bits = $vector->to_Bin;
    $bits =~ s/([01]{6})/$inverted{$1}/ge;
    say $bits;
}

__DATA__
123456

ZZZZZZ
ABCDEF

[download]
I know, Bit::Vector is an XS-module, so it doesn't comply with your specs.

On my old laptop, it reads a file of 1 million strings, converts them to the compacted format and reconverts them to the original format (to make sure it worked) in 100 seconds.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: Fast - Compact That String by CountZero
in thread Fast - Compact That String by Limbic~Region

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