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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;