Copyright (c) 2017 Microsoft Corporation
Module Name:
dd_bdd
Abstract:
Simple BDD package modeled after BuDDy, which is modeled after CUDD.
Author:
Nikolaj Bjorner (nbjorner) 2017-10-13
Revision History:
--*/
#pragma once
#include "util/vector.h"
#include "util/map.h"
#include "util/small_object_allocator.h"
namespace dd {
class bdd;
class bdd_manager {
friend bdd;
typedef unsigned BDD;
const BDD null_bdd = UINT_MAX;
enum bdd_op {
bdd_and_op = 2,
bdd_or_op = 3,
bdd_xor_op = 4,
bdd_not_op = 5,
bdd_and_proj_op = 6,
bdd_or_proj_op = 7,
bdd_no_op = 8,
};
struct bdd_node {
bdd_node(unsigned level, BDD lo, BDD hi):
m_refcount(0),
m_level(level),
m_lo(lo),
m_hi(hi),
m_index(0)
{}
bdd_node(): m_refcount(0), m_level(0), m_lo(0), m_hi(0), m_index(0) {}
unsigned m_refcount : 10;
unsigned m_level : 22;
BDD m_lo;
BDD m_hi;
unsigned m_index;
unsigned hash() const { return mk_mix(m_level, m_lo, m_hi); }
bool is_internal() const { return m_lo == 0 && m_hi == 0; }
void set_internal() { m_lo = 0; m_hi = 0; }
};
enum cost_metric {
cnf_cost,
dnf_cost,
bdd_cost
};
struct hash_node {
unsigned operator()(bdd_node const& n) const { return n.hash(); }
};
struct eq_node {
bool operator()(bdd_node const& a, bdd_node const& b) const {
return a.m_lo == b.m_lo && a.m_hi == b.m_hi && a.m_level == b.m_level;
}
};
typedef hashtable<bdd_node, hash_node, eq_node> node_table;
struct op_entry {
op_entry(BDD l, BDD r, BDD op):
m_bdd1(l),
m_bdd2(r),
m_op(op),
m_result(0)
{}
BDD m_bdd1;
BDD m_bdd2;
BDD m_op;
BDD m_result;
unsigned hash() const { return mk_mix(m_bdd1, m_bdd2, m_op); }
};
struct hash_entry {
unsigned operator()(op_entry* e) const { return e->hash(); }
};
struct eq_entry {
bool operator()(op_entry * a, op_entry * b) const {
return a->m_bdd1 == b->m_bdd2 && a->m_bdd2 == b->m_bdd2 && a->m_op == b->m_op;
}
};
typedef ptr_hashtable<op_entry, hash_entry, eq_entry> op_table;
svector<bdd_node> m_nodes;
op_table m_op_cache;
node_table m_node_table;
unsigned_vector m_apply_const;
svector<BDD> m_bdd_stack;
op_entry* m_spare_entry;
svector<BDD> m_var2bdd;
unsigned_vector m_var2level, m_level2var;
unsigned_vector m_free_nodes;
small_object_allocator m_alloc;
mutable svector<unsigned> m_mark;
mutable unsigned m_mark_level;
mutable svector<double> m_count;
mutable svector<BDD> m_todo;
bool m_disable_gc;
bool m_is_new_node;
unsigned m_max_num_bdd_nodes;
unsigned_vector m_S, m_T, m_to_free;
vector<unsigned_vector> m_level2nodes;
unsigned_vector m_reorder_rc;
cost_metric m_cost_metric;
BDD m_cost_bdd;
BDD make_node(unsigned level, BDD l, BDD r);
bool is_new_node() const { return m_is_new_node; }
BDD apply_const(BDD a, BDD b, bdd_op op);
BDD apply(BDD arg1, BDD arg2, bdd_op op);
BDD mk_quant(unsigned n, unsigned const* vars, BDD b, bdd_op op);
BDD apply_rec(BDD arg1, BDD arg2, bdd_op op);
BDD mk_not_rec(BDD b);
BDD mk_ite_rec(BDD a, BDD b, BDD c);
BDD mk_quant_rec(unsigned lvl, BDD b, bdd_op op);
void push(BDD b);
void pop(unsigned num_scopes);
BDD read(unsigned index);
op_entry* pop_entry(BDD l, BDD r, BDD op);
void push_entry(op_entry* e);
bool check_result(op_entry*& e1, op_entry const* e2, BDD a, BDD b, BDD c);
double count(BDD b, unsigned z);
void alloc_free_nodes(unsigned n);
void init_mark();
void set_mark(unsigned i) { m_mark[i] = m_mark_level; }
bool is_marked(unsigned i) { return m_mark[i] == m_mark_level; }
void init_reorder();
void reorder_incref(unsigned n);
void reorder_decref(unsigned n);
void sift_up(unsigned level);
void sift_var(unsigned v);
double current_cost();
bool is_bad_cost(double new_cost, double best_cost) const;
static const BDD false_bdd = 0;
static const BDD true_bdd = 1;
static const unsigned max_rc = (1 << 10) - 1;
inline bool is_true(BDD b) const { return b == true_bdd; }
inline bool is_false(BDD b) const { return b == false_bdd; }
inline bool is_const(BDD b) const { return b <= 1; }
inline unsigned level(BDD b) const { return m_nodes[b].m_level; }
inline unsigned var(BDD b) const { return m_level2var[level(b)]; }
inline BDD lo(BDD b) const { return m_nodes[b].m_lo; }
inline BDD hi(BDD b) const { return m_nodes[b].m_hi; }
inline void inc_ref(BDD b) { if (m_nodes[b].m_refcount != max_rc) m_nodes[b].m_refcount++; VERIFY(!m_free_nodes.contains(b)); }
inline void dec_ref(BDD b) { if (m_nodes[b].m_refcount != max_rc) m_nodes[b].m_refcount--; VERIFY(!m_free_nodes.contains(b)); }
inline BDD level2bdd(unsigned l) const { return m_var2bdd[m_level2var[l]]; }
double dnf_size(BDD b) { return count(b, 0); }
double cnf_size(BDD b) { return count(b, 1); }
unsigned bdd_size(bdd const& b);
bdd mk_not(bdd b);
bdd mk_and(bdd const& a, bdd const& b);
bdd mk_or(bdd const& a, bdd const& b);
bdd mk_xor(bdd const& a, bdd const& b);
void reserve_var(unsigned v);
bool well_formed();
struct scoped_push {
bdd_manager& m;
unsigned m_size;
scoped_push(bdd_manager& m) :m(m), m_size(m.m_bdd_stack.size()) {}
~scoped_push() { m.m_bdd_stack.shrink(m_size); }
};
public:
struct mem_out {};
bdd_manager(unsigned nodes);
~bdd_manager();
void set_max_num_nodes(unsigned n) { m_max_num_bdd_nodes = n; }
bdd mk_var(unsigned i);
bdd mk_nvar(unsigned i);
bdd mk_true();
bdd mk_false();
bdd mk_exists(unsigned n, unsigned const* vars, bdd const & b);
bdd mk_forall(unsigned n, unsigned const* vars, bdd const & b);
bdd mk_exists(unsigned v, bdd const& b);
bdd mk_forall(unsigned v, bdd const& b);
bdd mk_ite(bdd const& c, bdd const& t, bdd const& e);
std::ostream& display(std::ostream& out);
std::ostream& display(std::ostream& out, bdd const& b);
void gc();
void try_reorder();
void try_cnf_reorder(bdd const& b);
};
class bdd {
friend class bdd_manager;
unsigned root;
bdd_manager* m;
bdd(unsigned root, bdd_manager* m): root(root), m(m) { m->inc_ref(root); }
public:
bdd(bdd const & other): root(other.root), m(other.m) { m->inc_ref(root); }
bdd(bdd && other) noexcept : root(0), m(other.m) { std::swap(root, other.root); }
bdd& operator=(bdd const& other);
~bdd() { m->dec_ref(root); }
bdd lo() const { return bdd(m->lo(root), m); }
bdd hi() const { return bdd(m->hi(root), m); }
unsigned var() const { return m->var(root); }
bool is_true() const { return root == bdd_manager::true_bdd; }
bool is_false() const { return root == bdd_manager::false_bdd; }
bdd operator!() { return m->mk_not(*this); }
bdd operator&&(bdd const& other) { return m->mk_and(*this, other); }
bdd operator||(bdd const& other) { return m->mk_or(*this, other); }
bdd operator^(bdd const& other) { return m->mk_xor(*this, other); }
bdd operator|=(bdd const& other) { return *this = *this || other; }
bdd operator&=(bdd const& other) { return *this = *this && other; }
std::ostream& display(std::ostream& out) const { return m->display(out, *this); }
bool operator==(bdd const& other) const { return root == other.root; }
bool operator!=(bdd const& other) const { return root != other.root; }
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); }
};
std::ostream& operator<<(std::ostream& out, bdd const& b);
}