// undo optimization shifting
if (shiftBefore > 0) {
RangeDifference first= (RangeDifference) diffs.get(0);
if (first.kind() == RangeDifference.NOCHANGE)
first.extendStart(-shiftBefore);
else
diffs.add(0, new RangeDifference(RangeDifference.NOCHANGE, first.rightStart() - shiftBefore, shiftBefore, first.leftStart() - shiftBefore, shiftBefore));
}
RangeDifference last= (RangeDifference) diffs.get(diffs.size() - 1);