presto-main/src/main/java/io/prestosql/operator/project/DictionaryAwarePageFilter.java/DictionaryAwarePageFilter/toPositionsMask
class DictionaryAwarePageFilter:    private static boolean[] toPositionsMask(SelectedPositions selectedPositions, int positionCount)
    {
        boolean[] positionsMask = new boolean[positionCount];
        if (selectedPositions.isList()) {
            int offset = selectedPositions.getOffset();
            int[] positions = selectedPositions.getPositions();
            for (int index = offset; index < offset + selectedPositions.size(); index++) {
                positionsMask[positions[index]] = true;
            }
        }
        else {
            int offset = selectedPositions.getOffset();
            for (int position = offset; position < offset + selectedPositions.size(); position++) {
                positionsMask[position] = true;
            }
        }
        return positionsMask;
    }