RangeList<T> subtract (Range<T> range, RangeList<T> sub)
{
/* Start with the input range */
RangeList<T> result;
result.add (range);
if (sub.empty () || range.empty()) {
return result;
}
typename RangeList<T>::List s = sub.get ();
/* The basic idea here is to keep a list of the result ranges, and subtract
the bits of `sub' from them one by one.
*/
for (typename RangeList<T>::List::const_iterator i = s.begin(); i != s.end(); ++i) {
/* Here's where we'll put the new current result after subtracting *i from it */
RangeList<T> new_result;
typename RangeList<T>::List r = result.get ();
/* Work on all parts of the current result using this range *i */
for (typename RangeList<T>::List::const_iterator j = r.begin(); j != r.end(); ++j) {
switch (coverage (j->from, j->to, i->from, i->to)) {
case OverlapNone:
/* The thing we're subtracting (*i) does not overlap this bit of the result (*j),
so pass it through.
*/
new_result.add (*j);
break;
case OverlapInternal:
/* Internal overlap of the thing we're subtracting (*i) from this bit of the result,
so we should end up with two bits of (*j) left over, from the start of (*j) to
the start of (*i), and from the end of (*i) to the end of (*j).
*/
assert (j->from < i->from);
assert (j->to > i->to);
new_result.add (Range<T> (j->from, i->from - 1));
new_result.add (Range<T> (i->to + 1, j->to));
break;
case OverlapStart:
/* The bit we're subtracting (*i) overlaps the start of the bit of the result (*j),
* so we keep only the part of of (*j) from after the end of (*i)
*/
assert (i->to < j->to);
new_result.add (Range<T> (i->to + 1, j->to));
break;
case OverlapEnd:
/* The bit we're subtracting (*i) overlaps the end of the bit of the result (*j),
* so we keep only the part of of (*j) from before the start of (*i)
*/
assert (j->from < i->from);
new_result.add (Range<T> (j->from, i->from - 1));
break;
case OverlapExternal:
/* total overlap of the bit we're subtracting with the result bit, so the
result bit is completely removed; do nothing */
break;
}
}
new_result.coalesce ();
result = new_result;
}
return result;
}
// Not empty set
inline bool
empty() const {
return ranges.empty();
}
