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#!/usr/bin/perl 
...
    my ( $x, $y ) = ( $val->[$_][0], $val->[$_][1] );
    print same_sign( $x, $y ) ? '' : 'not ', "same sign\n";
}

 1  2 => same sign
-1  2 => not same sign
 1 -2 => not same sign
-1 -2 => same sign