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$_ = [
    [
...
    ]
];
(%_) = %{ ${ ${ $_; }[0]; }[1]; };

undef $_;
%_ = (
...
            65 => '011100001001010100000001'
#                  012345678901234567890123
);

$s = eval {
    do {
...

      }
};

$o = pack( 'b*', $_{9} );
foreach $_ ( 0 .. unpack( '%b*', $o ) - 2 ) {
# 16 bit checksum = 25, - 2 = 23

    $c = $_ - ( ( $_ - $_ % 4 ) / 4 + ( $_ % 4 ? 1 : 0 ) );
# print $c;
...
#    1010  0010  0000  1111  0001  0100  0000  0100  1000  1000  0101 
+ 0100
# J  u  r  t        n  o  u  h  e  r     P  d  r  l  a  h  a  b  j  e 
+ r
#       *        *        *                 *        *        *  *

    $i += $i % 2 ? -1 : 1 # $i ^= 1
      if ( $_ + 1 ) % 12 and not(( $_ + 1 ) % 3)
...
# print $i % 16;
# 10 5 3 4 0 1 14 15 4 8 5 2 0 0 5 2 12 0 8 1 3 11 5 2
# J  u s t   a n  o  t h e r   P e r l    h a c k  e r

    $T =
      vec( pack( 'C', $i ), 0, 4 ) + vec( pack( 'b*', $_{65} ), $_, 1 
+) * 16 +
...
# 0  1  1  1  0  0  0  0  1  0  0  1  0  1  0  1  0  0  0  0  0  0  0 
+ 1
# J  u  s  t     a  n  o  t  h  e  r     P  e  r  l     h  a  c  k  e 
+ r
# *  1  2  3  4  5  6  7  8  9  10 11 12 *  1  2  3  4  5  6  7  8  9 
+ 10

    print pack( 'c', ( $T += $T == 32 ? 0 : 64 ) -= $_ % 13 == 0 ? 32 
+: 0 );

#    &$s; # independent of rest of loop, unrolled
}
...
# 00   14294967295  2105  38   44294967263  573   68   74294967263  87
+7
# 94   104294967291 1153  120  134294967295 14116 1520 164294967263 17
+112
# 1813 194294967282 20125 2116 224294967295 23116

print pack( 'c', &$s(1) ^ unpack( 'c', pack( 'b*', $_{72} ) ) );