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min_parity at most N

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This commit is contained in:
Jakob Rath 2023-03-11 23:23:32 +01:00
parent d4428c6cef
commit f7baba4091
1 changed files with 17 additions and 15 deletions
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32
src/math/polysat/saturation.cpp
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@ -913,26 +913,27 @@ namespace polysat {
* parity(x) <= i, parity(y) >= j => parity(a) >= j - i
* parity(x) >= i, parity(y) <= j => parity(a) <= j - i
* symmetric rules for swapping x, a
*
* min_parity(x) = number of trailing bits of x if x is a value
*
* min_parity(x) = N if x = 0
* min_parity(x) = number of trailing bits of x if x is a non-zero value
* min_parity(x) = k if 2^{N-k}*x == 0 is forced for max k
* min_parity(x1*x2) = min_parity(x1) + min_parity(x2)
* min_parity(x) = 0, otherwise
*
* max_parity(x) = number of trailing bits of x
*
* max_parity(x) = N if x = 0
* max_parity(x) = number of trailing bits of x if x is a non-zero value
* max_parity(x) = k if 2^{N-k-1}*x != 0 for min k
* max_parity(x1*x2) = max_parity(x1) + max_parity(x2)
* max_parity(x) = N, otherwise
*
*
*/
unsigned saturation::min_parity(pdd const& p, vector<signed_constraint>& explain) {
rational val;
auto& m = p.manager();
unsigned N = m.power_of_2();
unsigned const N = m.power_of_2();
if (p.is_val())
return p.val().parity(N);
rational val;
if (s.try_eval(p, val)) {
unsigned k = val.parity(N);
if (k > 0)
@ -941,20 +942,21 @@ namespace polysat {
}
unsigned min = 0;
unsigned sz = explain.size();
unsigned const sz = explain.size();
if (!p.is_var()) {
// parity of a product => sum of parities
// parity of sum => minimum of monomial's minimal parities
min = UINT32_MAX;
for (const auto& monomial : p) {
min = N;
for (auto const& monomial : p) {
SASSERT(!monomial.coeff.is_zero());
unsigned parity_sum = monomial.coeff.trailing_zeros();
for (pvar c : monomial.vars)
parity_sum += min_parity(m.mk_var(c), explain);
for (pvar v : monomial.vars)
parity_sum += min_parity(m.mk_var(v), explain);
min = std::min(min, parity_sum);
}
}
SASSERT(min <= N);
for (unsigned j = N; j > min; --j)
if (is_forced_true(s.parity_at_least(p, j))) {
explain.shrink(sz);