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Add BDD utilities; use them for narrowing/propagation of linear equality constraints (#5192)

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* Add a few helper methods for encoding sets of integers as BDDs

* Use BDD functions in solver

* Add bdd::find_int

* Use bdd::find_int in solver

* Add narrowing for linear equality constraints

* Simplify code for linear propagation

* Add test for later

* Narrowing can only handle linear constraints with a single variable

* Need to push_cjust
This commit is contained in:
Jakob Rath 2021-04-16 17:44:18 +02:00 • committed by GitHub
parent e970fe5034
commit f72e30e539
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10 changed files with 208 additions and 104 deletions
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26
src/math/dd/dd_bdd.h
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@ -21,11 +21,14 @@ Revision History:
#include "util/vector.h"
#include "util/map.h"
#include "util/small_object_allocator.h"
#include "util/rational.h"
namespace dd {
class bdd;
enum class find_int_t { empty, singleton, multiple };
class bdd_manager {
friend bdd;
@ -189,6 +192,9 @@ namespace dd {
bdd mk_or(bdd const& a, bdd const& b);
bdd mk_xor(bdd const& a, bdd const& b);
bool contains_int(BDD b, rational const& val, unsigned w);
find_int_t find_int(BDD b, unsigned w, rational& val);
void reserve_var(unsigned v);
bool well_formed();
@ -219,6 +225,20 @@ namespace dd {
bdd mk_forall(unsigned v, bdd const& b);
bdd mk_ite(bdd const& c, bdd const& t, bdd const& e);
/** Encodes the lower w bits of val as BDD, using variable indices 0 to w-1.
* The least-significant bit is encoded as variable 0.
* val must be an integer.
*/
bdd mk_int(rational const& val, unsigned w);
/** Encodes the solutions of the affine relation
*
* a*x + b == 0 (mod 2^w)
*
* as BDD.
*/
bdd mk_affine(rational const& a, rational const& b, unsigned w);
std::ostream& display(std::ostream& out);
std::ostream& display(std::ostream& out, bdd const& b);
@ -256,6 +276,12 @@ namespace dd {
double cnf_size() const { return m->cnf_size(root); }
double dnf_size() const { return m->dnf_size(root); }
unsigned bdd_size() const { return m->bdd_size(*this); }
/** Checks whether the integer val is contained in the BDD when viewed as set of integers (see also mk_int). */
bool contains_int(rational const& val, unsigned w) { return m->contains_int(root, val, w); }
/** Returns an integer contained in the BDD, if any, and whether the BDD is a singleton. */
find_int_t find_int(unsigned w, rational& val) { return m->find_int(root, w, val); }
};
std::ostream& operator<<(std::ostream& out, bdd const& b);