mirrors/z3
3
0
Fork 0
mirror of https://github.com/Z3Prover/z3 synced 2025-05-14 03:04:44 +00:00
Code Activity

add new file for eq_constraint

Browse source 
Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-04-15 14:34:01 -07:00
parent c733789467
commit 2eadcd586a
6 changed files with 161 additions and 149 deletions
Download patch file Download diff file Expand all files Collapse all files

123
src/math/polysat/constraint.cpp
View file

@ -29,127 +29,4 @@ namespace polysat {
return alloc(eq_constraint, lvl, p, d);
}
std::ostream& eq_constraint::display(std::ostream& out) const {
return out << p() << " == 0";
}
bool eq_constraint::propagate(solver& s, pvar v) {
LOG_H3("Propagate " << s.m_vars[v] << " in " << *this);
SASSERT(!vars().empty());
auto var = s.m_vars[v].var();
unsigned idx = 0;
if (vars()[idx] != v)
idx = 1;
SASSERT(v == vars()[idx]);
// find other watch variable.
for (unsigned i = vars().size(); i-- > 2; ) {
if (!s.is_assigned(vars()[i])) {
std::swap(vars()[idx], vars()[i]);
return true;
}
}
LOG("Assignments: " << s.m_search);
auto q = p().subst_val(s.m_search);
LOG("Substituted: " << p() << " := " << q);
TRACE("polysat", tout << p() << " := " << q << "\n";);
if (q.is_zero())
return false;
if (q.is_never_zero()) {
LOG("Conflict (never zero under current assignment)");
// we could tag constraint to allow early substitution before
// swapping watch variable in case we can detect conflict earlier.
s.set_conflict(*this);
return false;
}
// at most one variable remains unassigned.
auto other_var = vars()[1 - idx];
// Detect and apply unit propagation.
if (!q.is_linear())
return false;
// a*x + b == 0
rational a = q.hi().val();
rational b = q.lo().val();
rational inv_a;
if (a.is_odd()) {
// v1 = -b * inverse(a)
unsigned sz = q.power_of_2();
VERIFY(a.mult_inverse(sz, inv_a));
rational val = mod(inv_a * -b, rational::power_of_two(sz));
s.m_cjust[other_var].push_back(this);
s.propagate(other_var, val, *this);
return false;
}
SASSERT(!b.is_odd()); // otherwise p.is_never_zero() would have been true above
// TBD
// constrain viable using condition on x
// 2*x + 2 == 0 mod 4 => x is odd
//
// We have:
// 2^j*a'*x + 2^j*b' == 0 mod m, where a' is odd (but not necessarily b')
// <=> 2^j*(a'*x + b') == 0 mod m
// <=> a'*x + b' == 0 mod (m-j)
// <=> x == -b' * inverse_{m-j}(a') mod (m-j)
// ( <=> 2^j*x == 2^j * -b' * inverse_{m-j}(a') mod m )
//
// x == c mod (m-j)
// Which x in 2^m satisfy this?
// => x \in { c + k * 2^(m-j) | k = 0, ..., 2^j - 1 }
unsigned rank_a = a.trailing_zeros(); // j
SASSERT(b == 0 || rank_a <= b.trailing_zeros());
rational aa = a / rational::power_of_two(rank_a); // a'
rational bb = b / rational::power_of_two(rank_a); // b'
rational inv_aa;
unsigned small_sz = q.power_of_2() - rank_a; // m - j
VERIFY(aa.mult_inverse(small_sz, inv_aa));
rational cc = mod(inv_aa * -bb, rational::power_of_two(small_sz));
LOG(m_vars[other_var] << " = " << cc << " + k * 2^" << small_sz);
// TODO: better way to update the BDD, e.g. construct new one (only if rank_a is small?)
vector<rational> viable;
for (rational k = rational::zero(); k < rational::power_of_two(rank_a); k += 1) {
rational val = cc + k * rational::power_of_two(small_sz);
viable.push_back(val);
}
LOG_V("still viable: " << viable);
unsigned i = 0;
for (rational r = rational::zero(); r < rational::power_of_two(q.power_of_2()); r += 1) {
while (i < viable.size() && viable[i] < r)
++i;
if (i < viable.size() && viable[i] == r)
continue;
if (s.is_viable(other_var, r)) {
s.add_non_viable(other_var, r);
}
}
LOG("TODO");
return false;
}
constraint* eq_constraint::resolve(solver& s, pvar v) {
if (s.m_conflict.size() != 1)
return nullptr;
constraint* c = s.m_conflict[0];
if (c->is_eq()) {
pdd a = c->to_eq().p();
pdd b = p();
pdd r = a;
if (!a.resolve(v, b, r))
return nullptr;
p_dependency_ref d(s.m_dm.mk_join(c->dep(), dep()), s.m_dm);
// d = ;
unsigned lvl = std::max(c->level(), level());
return constraint::eq(lvl, r, d);
}
return nullptr;
}
}