Looking at the Wikipedia page it should be straightforward. That's what I thought until I saw your example. Why should the result be 7? Should it not be 8? I would think you should do

my @corners = ( 1, 0, 0, 0 );
my $index = 0;
( $index <<= 1 ) |= $_ for @corners;
print "$index\n";
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which is nothing but translating binary 1000 into decimal (and which can be achieved in a zillion ways in Perl...