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https://github.com/Z3Prover/z3
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77350d97da
* Coding style * Simplify bddv class * mk_eq: run loop from below * Add unit test for bddv unsigned comparison * Add test that shows contains_num/find_num fail after reordering * Add BDD vector subtraction * Call apply_rec in mk_ite_rec instead of apply * Question about mk_quant * Implement quot_rem over BDD vectors * Move shl/shr to bddv * Make unit test smaller * Add class dd::fdd to manage association between BDDs and numbers * Remove contains_num/find_num from bdd_manager
128 lines
3.8 KiB
C++
128 lines
3.8 KiB
C++
/*++
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Copyright (c) 2021 Microsoft Corporation
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Module Name:
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polysat eq_constraints
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Author:
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Nikolaj Bjorner (nbjorner) 2021-03-19
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Jakob Rath 2021-04-6
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--*/
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#include "math/polysat/constraint.h"
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#include "math/polysat/solver.h"
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#include "math/polysat/log.h"
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namespace polysat {
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std::ostream& eq_constraint::display(std::ostream& out) const {
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return out << p() << " == 0";
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}
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bool eq_constraint::propagate(solver& s, pvar v) {
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LOG_H3("Propagate " << s.m_vars[v] << " in " << *this);
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SASSERT(!vars().empty());
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unsigned idx = 0;
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if (vars()[idx] != v)
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idx = 1;
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SASSERT(v == vars()[idx]);
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// find other watch variable.
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for (unsigned i = vars().size(); i-- > 2; ) {
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if (!s.is_assigned(vars()[i])) {
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std::swap(vars()[idx], vars()[i]);
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return true;
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}
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}
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LOG("Assignments: " << s.m_search);
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auto q = p().subst_val(s.m_search);
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LOG("Substituted: " << p() << " := " << q);
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TRACE("polysat", tout << p() << " := " << q << "\n";);
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if (q.is_zero())
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return false;
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if (q.is_never_zero()) {
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LOG("Conflict (never zero under current assignment)");
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s.set_conflict(*this);
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return false;
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}
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// at most one variable remains unassigned.
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auto other_var = vars()[1 - idx];
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SASSERT(!q.is_val() && q.var() == other_var);
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// Detect and apply unit propagation.
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if (try_narrow_with(q, s)) {
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rational val;
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switch (s.find_viable(other_var, val)) {
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case dd::find_t::empty:
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s.set_conflict(*this);
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return false;
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case dd::find_t::singleton:
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s.propagate(other_var, val, *this);
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return false;
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case dd::find_t::multiple:
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/* do nothing */
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break;
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}
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}
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return false;
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}
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constraint* eq_constraint::resolve(solver& s, pvar v) {
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if (s.m_conflict.size() != 1)
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return nullptr;
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constraint* c = s.m_conflict[0];
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if (c->is_eq()) {
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pdd a = c->to_eq().p();
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pdd b = p();
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pdd r = a;
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if (!a.resolve(v, b, r))
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return nullptr;
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p_dependency_ref d(s.m_dm.mk_join(c->dep(), dep()), s.m_dm);
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unsigned lvl = std::max(c->level(), level());
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return constraint::eq(lvl, r, d);
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}
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return nullptr;
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}
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bool eq_constraint::try_narrow_with(pdd const& q, solver& s) {
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if (q.is_linear() && q.free_vars().size() == 1) {
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// a*x + b == 0
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pvar v = q.var();
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rational a = q.hi().val();
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rational b = q.lo().val();
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bddv const& x = s.sz2bits(s.size(v)).var();
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bdd xs = (a * x + b == rational(0));
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s.intersect_viable(v, xs);
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s.push_cjust(v, this);
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return true;
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}
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// TODO: what other constraints can be extracted cheaply?
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return false;
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}
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void eq_constraint::narrow(solver& s) {
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// NSB code review:
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// This should also use the current assignment so be similar to propagate.
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// The idea is that narrow is invoked when the constraint is first added
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// and also when the constraint is used in a conflict.
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// When it is used in a conflict, there could be a partial assignment in s.m_search
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// that fixes variables in p().
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//
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(void)try_narrow_with(p(), s);
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}
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bool eq_constraint::is_always_false() {
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return p().is_never_zero();
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}
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bool eq_constraint::is_currently_false(solver& s) {
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pdd r = p().subst_val(s.m_search);
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return r.is_never_zero();
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}
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}
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