Abstract: A data structure includes an array having at least a first element, a second element and a third element. The first element represents a first bit of a first entry and a first bit of a second entry, wherein the first bit of the first entry is at the same position as, but has a different value from, the first bit of the entry. The first element stores a reference to only the second element. The second element represents a second bit of the first entry, the second bit of the first entry having a position next to the first bit of the first entry. The third element represents a second bit of the second entry, the second bit of the second entry having a position next to the first bit of the second entry. The third element is stored adjacent to the first element in the array.