If I have four corners with the values 1,0,0,0 how would I go about building the index - for these values the result should be 7.

Erm. Binary 1000 is 8 not 7. Unless you invert the bits, but I don't see any call for that in a quick scan of the page you linked.

If you have an 4 element array containing the 1s & 0s, you could build the numeric value this way:

@b = qw[ 1 0 0 0 ];;

$n = 0; 
$n <<= 1, $n |= $_  for @b; 

print $n;;
8


@b = qw[ 0 1 1 1 ];;

$n = 0; 
$n <<= 1, $n |= $_  for @b; 

print $n;;
7
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