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Multiply by inverse to detect more parity constraints

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Clemens Eisenhofer 2023-02-18 14:15:51 +01:00
parent ae70a8e9f0
commit e8b4875a17
3 changed files with 21 additions and 9 deletions
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22
src/math/polysat/simplify_clause.cpp
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@ -349,7 +349,7 @@ namespace polysat {
}
// decomposes into a plain constant and a part containing variables. e.g., 2*x*y + 3*z - 2 gets { 2*x*y + 3*z, -2 }
static std::pair<pdd, pdd> decompose_constant(const pdd& p) {
static std::pair<pdd, pdd> decouple_constant(const pdd& p) {
for (const auto& m : p) {
if (m.vars.empty())
return { p - m.coeff, p.manager().mk_val(m.coeff) };
@ -358,10 +358,9 @@ namespace polysat {
}
// 2^(k - d) * x = m * 2^(k - d)
// TODO: Factor out constant factors from x and put them to the rhs
bool simplify_clause::get_trailing_mask(pdd lhs, pdd rhs, pdd& p, trailing_bits& mask, bool pos) {
auto lhs_decomp = decompose_constant(lhs);
auto rhs_decomp = decompose_constant(rhs);
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;
@ -371,7 +370,7 @@ namespace polysat {
unsigned k = lhs.manager().power_of_2();
unsigned d = lhs.max_pow2_divisor();
unsigned span = k - d;
if (span == 0)
if (span == 0 || lhs.is_val())
return false;
p = lhs.div(rational::power_of_two(d));
@ -379,6 +378,19 @@ namespace polysat {
mask.bits = rhs_val / rational::power_of_two(d);
if (!mask.bits.is_int())
return false;
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;
mask.bits *= inv;
}
mask.length = span;
mask.positive = pos;
return true;

7
src/math/polysat/variable_elimination.cpp
View file

@ -764,9 +764,9 @@ namespace polysat {
if (a_parity > 0) {
shift = s.lshr(a1, a1.manager().mk_val(a_parity));
signed_constraint least_parity = s.parity_at_least(a1, a_parity);
signed_constraint shift_right_left = s.eq(rational::power_of_two(a_parity) * shift, a1);
s.add_clause(~least_parity, shift_right_left, true);
//signed_constraint least_parity = s.parity_at_least(a1, a_parity);
//signed_constraint shift_right_left = s.eq(rational::power_of_two(a_parity) * shift, a1);
//s.add_clause(~least_parity, shift_right_left, true);
// s.add_clause(~shift_right_left, least_parity, true); Might be interesting as well [although not needed]; needs to consider special case 0
// [nsb cr: this pre-condition is already implied from the parity explanations]
// precondition.insert_eval(~shift_right_left);
@ -778,7 +778,6 @@ namespace polysat {
LOG("pseudo inverse: " << a_pi);
LOG("-b: " << (-b));
LOG("shifted a" << shift);
LOG("Forced elimination: " << a_pi * (-b) * shift + b1);
return { a_pi * (-b) * shift + b1, true };
#endif
}

1
src/math/polysat/viable.cpp
View file

@ -913,6 +913,7 @@ namespace {
do {
if (e->src.size() != 1) {
// We just consider the ordinary constraints and not already contracted ones
e = e->next();
continue;
}