for my $x (0 .. $rows ) { for my $y ( 0 .. $cols) { my $s = $table->[$x][$y] + ($y ? $table->[$x][$y-1] : 0) + ($x ? $table->[$x-1][$y] : 0) - (($x && $y) ? $table->[$x-1][$y-1] : 0); $table->[$x][$y]=$s; } }