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Frequent lsb special case

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This commit is contained in:
Clemens Eisenhofer 2023-03-07 18:07:39 +01:00
parent f059b5e16b
commit 60a405d134
2 changed files with 84 additions and 35 deletions
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100
src/math/polysat/simplify_clause.cpp
View file

@ -358,49 +358,78 @@ namespace polysat {
}
// 2^(k - d) * x = m * 2^(k - d)
// Special case [still seems to occur frequently]: -2^(k - 2) * x > 2^(k - 1) - TODO: Generalize [the obvious solution does not work] => lsb(x, 2) = 1
bool simplify_clause::get_lsb(pdd lhs, pdd rhs, pdd& p, trailing_bits& info, bool pos) {
auto lhs_decomp = decouple_constant(lhs);
auto rhs_decomp = decouple_constant(rhs);
lhs = lhs_decomp.first - rhs_decomp.first;
rhs = rhs_decomp.second - lhs_decomp.second;
SASSERT(rhs.is_val());
unsigned k = lhs.manager().power_of_2();
unsigned d = lhs.max_pow2_divisor();
unsigned span = k - d;
if (span == 0 || lhs.is_val())
return false;
p = lhs.div(rational::power_of_two(d));
rational rhs_val = rhs.val();
info.bits = rhs_val / rational::power_of_two(d);
if (!info.bits.is_int())
return false;
SASSERT(lhs.is_univariate() && lhs.degree() <= 1);
SASSERT(rhs.is_univariate() && rhs.degree() <= 1);
auto it = p.begin();
auto first = *it;
it++;
if (it == p.end()) {
// if the lhs contains only one monomial it is of the form: odd * x = mask. We can multiply by the inverse to get the mask for x
SASSERT(first.coeff.is_odd());
rational inv;
VERIFY(first.coeff.mult_inverse(lhs.power_of_2(), inv));
p *= inv;
info.bits = mod2k(info.bits * inv, span);
if (rhs.is_zero()) { // equality
auto lhs_decomp = decouple_constant(lhs);
lhs = lhs_decomp.first;
rhs = -lhs_decomp.second;
SASSERT(rhs.is_val());
unsigned k = lhs.manager().power_of_2();
unsigned d = lhs.max_pow2_divisor();
unsigned span = k - d;
if (span == 0 || lhs.is_val())
return false;
p = lhs.div(rational::power_of_two(d));
rational rhs_val = rhs.val();
info.bits = rhs_val / rational::power_of_two(d);
if (!info.bits.is_int())
return false;
SASSERT(lhs.is_univariate() && lhs.degree() <= 1);
auto it = p.begin();
auto first = *it;
it++;
if (it == p.end()) {
// if the lhs contains only one monomial it is of the form: odd * x = mask. We can multiply by the inverse to get the mask for x
SASSERT(first.coeff.is_odd());
rational inv;
VERIFY(first.coeff.mult_inverse(lhs.power_of_2(), inv));
p *= inv;
info.bits = mod2k(info.bits * inv, span);
}
info.length = span;
info.positive = pos;
return true;
}
else { // inequality - check for special case
if (pos || lhs.power_of_2() < 3)
return false;
auto it = lhs.begin();
if (it == lhs.end())
return false;
if (it->vars.size() != 1)
return false;
rational coeff = it->coeff;
it++;
if (it != lhs.end())
return false;
if ((mod2k(-coeff, lhs.power_of_2())) != rational::power_of_two(lhs.power_of_2() - 2))
return false;
p = lhs.div(coeff);
SASSERT(p.is_var());
info.bits = 1;
info.length = 2;
info.positive = true; // this is a conjunction
return true;
}
info.length = span;
info.positive = pos;
return true;
}
// 2^k - 2^(k - i) <= x -> first i bits 1
// 2^(k - i) > x -> first i bits 0
bool simplify_clause::get_msb(pdd lhs, pdd rhs, pdd& p, leading_bits& info, bool pos) {
SASSERT(lhs.is_univariate() && lhs.degree() <= 1);
SASSERT(rhs.is_univariate() && rhs.degree() <= 1);
if (lhs.is_var() && rhs.is_val()) {
if (rhs.is_zero())
return false;
@ -439,7 +468,10 @@ namespace polysat {
// 2^(k - 1) <= 2^(k - i - 1) * x (original definition)
// 2^(k - i - 1) * x + 2^(k - 1) <= 2^(k - 1) - 1 (rewritten)
bool simplify_clause::get_bit(const pdd& lhs, const pdd& rhs, pdd& p, single_bit& bit, bool pos) {
SASSERT(lhs.is_univariate() && lhs.degree() <= 1);
SASSERT(rhs.is_univariate() && rhs.degree() <= 1);
unsigned k = rhs.power_of_2();
if (rhs.is_val()) {
// 2^(k - i - 1) * x + 2^(k - 1) <= 2^(k - 1) - 1
rational rhs_val = rhs.val() + 1;

19
src/test/polysat.cpp
View file

@ -697,7 +697,22 @@ namespace polysat {
vector<ptr_vector<viable::entry>> justifications;
VERIFY(!s.m_viable.collect_bit_information(x.var(), false, fixed, justifications));
}
// parity(x) >= 1 and bit_1(x)
static void test_fi_quickcheck3() {
scoped_solver s(__func__);
auto x = s.var(s.add_var(256));
signed_constraint c1 = s.eq(rational::power_of_two(255) * x);
signed_constraint c2 = s.ult(rational::power_of_two(255), -rational::power_of_two(254) * x);
s.add_clause(c1, false);
s.add_clause(c2, false);
s.m_viable.intersect(x.var(), c1);
s.m_viable.intersect(x.var(), c2);
svector<lbool> fixed;
vector<ptr_vector<viable::entry>> justifications;
VERIFY(!s.m_viable.collect_bit_information(x.var(), false, fixed, justifications));
}
// 8 * x + 3 == 0 or 8 * x + 5 == 0 is unsat
static void test_parity1() {
scoped_solver s(__func__);
@ -2069,6 +2084,8 @@ void tst_polysat() {
RUN(test_polysat::test_fi_quickcheck1());
RUN(test_polysat::test_fi_quickcheck2());
RUN(test_polysat::test_fi_quickcheck3());
if (collect_test_records)
test_records.display(std::cout);
}