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Fix lshr axioms

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This commit is contained in:
Jakob Rath 2022-11-17 17:04:04 +01:00
parent 80a2ac64de
commit 68707eefe7
1 changed files with 28 additions and 27 deletions
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55
src/math/polysat/op_constraint.cpp
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@ -158,28 +158,29 @@ namespace polysat {
/**
* Enforce basic axioms for r == p >> q:
*
* q >= k -> r[i] = 0 for i > K - k
* q >= K -> r = 0
* q >= k -> r <= 2^{K-k-1}
* q = k -> r[i - k] = p[i] for i <= K - k
* r <= p
* q != 0 => r <= p
* q = 0 => r = p
* q >= K -> r = 0
* q >= k -> r[i] = 0 for K - k <= i < K (bit indices range from 0 to K-1, inclusive)
* q >= k -> r <= 2^{K-k} - 1
* q = k -> r[i] = p[i+k] for 0 <= i < K - k
* r <= p
* q != 0 -> r <= p (subsumed by previous axiom)
* q != 0 /\ p > 0 -> r < p
* q = 0 -> r = p
*
* when q is a constant, several axioms can be enforced at activation time.
*
* Enforce also inferences and bounds
*
* TODO use also
* TODO: use also
* s.m_viable.min_viable();
* s.m_viable.max_viable()
* when r, q are variables.
*/
void op_constraint::narrow_lshr(solver& s) {
auto pv = s.subst(p());
auto qv = s.subst(q());
auto rv = s.subst(r());
unsigned K = p().manager().power_of_2();
auto const pv = s.subst(p());
auto const qv = s.subst(q());
auto const rv = s.subst(r());
unsigned const K = p().manager().power_of_2();
signed_constraint lshr(this, true);
@ -192,26 +193,23 @@ namespace polysat {
else if (qv.is_zero() && pv.is_val() && rv.is_val() && pv != rv)
// q = 0 -> p = r
s.add_clause(~lshr, ~s.eq(q()), s.eq(p(), r()), true);
else if (qv.is_val() && !qv.is_zero() && pv.is_val() && rv.is_val() && !pv.is_zero() && pv.val() <= rv.val())
// q != 0 & p > 0 => r < p
else if (qv.is_val() && !qv.is_zero() && pv.is_val() && rv.is_val() && !pv.is_zero() && rv.val() >= pv.val())
// q != 0 & p > 0 -> r < p
s.add_clause(~lshr, s.eq(q()), s.ule(p(), 0), s.ult(r(), p()), true);
else if (qv.is_val() && !qv.is_zero() && qv.val() < K && rv.is_val() &&
rv.val() > rational::power_of_two(K - qv.val().get_unsigned() - 1))
// q >= k -> r <= 2^{K-k-1}
s.add_clause(~lshr, ~s.ule(qv.val(), q()), s.ule(r(), rational::power_of_two(K - qv.val().get_unsigned() - 1)), true);
else if (qv.is_val() && qv.val() >= K && rv.is_val() && !rv.is_zero())
// q >= K -> r = 0
s.add_clause(~lshr, ~s.ule(K, q()), s.eq(r()), true);
// q = k -> r[i - k] = p[i] for K - k <= i < K
rv.val() > rational::power_of_two(K - qv.val().get_unsigned()) - 1)
// q >= k -> r <= 2^{K-k} - 1
s.add_clause(~lshr, ~s.ule(qv.val(), q()), s.ule(r(), rational::power_of_two(K - qv.val().get_unsigned()) - 1), true);
else if (pv.is_val() && rv.is_val() && qv.is_val() && !qv.is_zero()) {
unsigned k = qv.val().get_unsigned();
for (unsigned i = K - k; i < K; ++i) {
if (rv.val().get_bit(i - k) && !pv.val().get_bit(i)) {
s.add_clause(~lshr, ~s.eq(q(), k), ~s.bit(r(), i - k), s.bit(p(), i), true);
unsigned const k = qv.val().get_unsigned();
// q = k -> r[i] = p[i+k] for 0 <= i < K - k
for (unsigned i = 0; i < K - k; ++i) {
if (rv.val().get_bit(i) && !pv.val().get_bit(i + k)) {
s.add_clause(~lshr, ~s.eq(q(), k), ~s.bit(r(), i), s.bit(p(), i + k), true);
return;
}
if (!rv.val().get_bit(i - k) && pv.val().get_bit(i)) {
s.add_clause(~lshr, ~s.eq(q(), k), s.bit(r(), i - k), ~s.bit(p(), i), true);
if (!rv.val().get_bit(i) && pv.val().get_bit(i + k)) {
s.add_clause(~lshr, ~s.eq(q(), k), s.bit(r(), i), ~s.bit(p(), i + k), true);
return;
}
}
@ -225,6 +223,9 @@ namespace polysat {
lbool op_constraint::eval_lshr(pdd const& p, pdd const& q, pdd const& r) {
auto& m = p.manager();
if (q.is_zero() && p == r)
return l_true;
if (q.is_val() && q.val() >= m.power_of_2() && r.is_val())
return to_lbool(r.is_zero());