void CommutativeRExpTest::testStar()
{
// 0* = 1
CPPUNIT_ASSERT( CommutativeRExp::null().star() == CommutativeRExp::one() );
CPPUNIT_ASSERT( a->star() == CommutativeRExp(CommutativeRExp::Star, std::shared_ptr<CommutativeRExp>(new CommutativeRExp(*a))));
}
// star the whole RExp
CommutativeRExp CommutativeRExp::star() const
{
if(this->type == Star)
return *this; // absorb the star
else if (this->type == Empty)
return one(); // {}* = ε
else
return CommutativeRExp(Star, std::shared_ptr<CommutativeRExp>(new CommutativeRExp(*this))); // star the element
}
void CommutativeRExpTest::testStar()
{
// 0* = 1
CPPUNIT_ASSERT( CommutativeRExp::null().star() == CommutativeRExp::one() );
CPPUNIT_ASSERT( a->star() == CommutativeRExp(CommutativeRExp::Star, std::shared_ptr<CommutativeRExp>(new CommutativeRExp(*a))));
// a.b^* != a.(a+b)^*
CPPUNIT_ASSERT( (*a) * (*b).star() != (*a) * ((*a) + (*b)).star());
}
// try to find a case of xx^* and convert it to x^+
void CommutativeRExp::optimize_starplus()
{
// we have to be careful, we will modify the set_copy!
// loop over all elements in the set and find the stared elements
std::shared_ptr<std::multiset<CommutativeRExp>> set_copy(new std::multiset<CommutativeRExp>());
*set_copy = *this->setm;
bool changed = false;
for(auto it = this->setm->begin(); it != this->setm->end(); ++it)
{
if(it->type == Star) // we found a stared element
{
// distinguish on the nested type
switch(it->rexp->type)
{
case Element: // easy, just try to find this element on the outer set, fall through case
case Addition: // addition behaves like an element in the original multiplication set
{
auto elem = set_copy->find(*it->rexp);
if(elem != set_copy->end())
{
// create x^+
auto plus_elem = CommutativeRExp(Plus, it->rexp);
// delete both x and x^*
set_copy->erase(*elem);
set_copy->erase(*it);
// then insert x^+
set_copy->insert(plus_elem);
changed = true;
}
break;
}
case Multiplication: // more tricky case, because the inner stared elements are distributed in the original multiplication set
{
bool found_all_elements = true;
// for every element in the starred multiplication
for(auto it2 = it->rexp->setm->begin(); it2 != it->rexp->setm->end(); ++it2)
{
auto elem = set_copy->find(*it2);
if(elem == set_copy->end())
{
found_all_elements = false;
break;
}
}
if(found_all_elements)
{
// create x^+
auto plus_elem = CommutativeRExp(Plus, it->rexp);
// delete both x and x^*
for(auto it2 = it->rexp->setm->begin(); it2 != it->rexp->setm->end(); ++it2)
set_copy->erase(*it2);
set_copy->erase(*it);
// then insert x^+
set_copy->insert(plus_elem);
changed = true;
}
break;
}
case Star: // should not happen, fall through
case Plus: // no idea, what to do, fall through
case Empty: // should not happen
assert(false); // we should have been optimizing this, debug more!
break;
}
}
}
if(changed)
this->setm = set_copy;
}
