$s = eval
{
    $index = 0; # $O
    $commabyte = 0; # $C
    $textstr = 'This is my 100th PM post'; # $t

    sub{
        $index++;
        $commabyte = @_ ? $commabyte :

                eval pack( 'b*', vec( pack( 'b*', $_{64} ), $index-1, 1 ) ? $_{1} : $_{8} ) .
                    $commabyte .
                    pack( 'c', vec( pack( 'b*', $_{64} ), ($index-1)%3, 8 ) ) .
                    pack( 'b*', vec( pack( 'b*', $_{64} ), $index-1, 1 ) ? $_{8} : $_{1} ) .
                    vec( $textstr, $index-1, 8 );
        };
};

##</code><code>##

1: pack( 'b*', vec( '&|^', $index-1, 1 ) ? '~' : '' )
2: $commabyte
3: pack( 'c', vec( '&|^', ($index-1)%3, 8 ) )
4: pack( 'b*', vec( '&|^', $index-1, 1 ) ? '' : '~' )
5: vec( $textstr, $index-1, 8 ) )

##</code><code>##

[~](char) (operator) [~](char)

##</code><code>##

bit: 01234567  low nybbles
j =  01010110   0101
u =  10101110      1010
s =  11001110         1100
t =  00101110            0010

##</code><code>##

$c = $offset - ( ($offset - ($offset % 4))/4 + ($offset % 4 ? 1 : 0) ); # first frame

$i = (
        (vec( $bitstr, $c, 4 ) +        # low nybble
        (vec( $bitstr, $c + 1, 4 )<<4)) # high nybble
        >> 4 - ($offset % 4) - 4 * ( ($offset % 4) ? 0 : 1 ) # shift off extra bits
      );

##</code><code>##

$i += $i%2 ? -1 : 1
	if(
		(  (($offset + 1) % 12) &&
		  !(($offset + 1) % 3)     ) ||
		$offset + 1 == 22 
	);

##</code><code>##

$T = vec( pack( 'C', $i ), 0, 4 ) +
	 vec( pack( 'b*', $_{65} ), $offset, 1 ) * (1<<4) +
	 (1<<5);

##</code><code>##

print pack( 'c',
            ($T += $T == (1<<5) ? 0 : (1<<6))
                -= $offset % 13 == 0 ? (1<<5) : 0 );