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@arr = qw ( up down in out left right );

@sel = ( 1, 3, 4 );

@my_items = Magic(@arr, @sel);

$bitmask = MoreMagic(@arr, @sel);

[...other work...]

@my_items = BetterMagic(@arr, $bitmask);

@arr = qw ( up down in out left right );  # 6 elements
@sel = ( 1, 3, 4 );
...
   printf("\$item: $item  \$mask: %0b\n", $mask);
}
printf("    final \$mask: %0b\n", $mask);