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inf

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-06-30 21:29:28 -07:00
parent 7d5a1acb61
commit 5edc939b85
2 changed files with 111 additions and 25 deletions
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134
src/math/dd/dd_fdd.cpp
View file

@ -120,6 +120,47 @@ namespace dd {
return out;
}
bool fdd::contains(bdd const& x, bool_vector const& value) const {
bdd b = x;
while (!b.is_true()) {
unsigned const pos = var2pos(b.var());
SASSERT(pos != UINT_MAX && "Unexpected BDD variable");
if (value[pos] && b.hi().is_false())
return false;
if (!value[pos] && b.lo().is_false())
return false;
if (value[pos])
b = b.hi();
else
b = b.lo();
}
return true;
}
// subtract one from x
static void dec(bool_vector& x) {
for (auto& b : x) {
b = !b;
if (!b)
break;
}
}
// add one to x
static void inc(bool_vector& x) {
for (auto& b : x) {
b = !b;
if (b)
break;
}
}
static void reset(bool_vector& x, bool value) {
for (auto& b : x)
b = value;
}
bool fdd::sup(bdd const& x, bool_vector& lo) const {
SASSERT(lo.size() == num_bits());
@ -128,20 +169,8 @@ namespace dd {
// after re-ordering. Then co-factoring is relatively cheap.
//
// this segment checks that lo is included in x
bdd b = x;
while (!b.is_true()) {
unsigned const pos = var2pos(b.var());
SASSERT(pos != UINT_MAX && "Unexpected BDD variable");
if (lo[pos] && b.hi().is_false())
return false;
if (!lo[pos] && b.lo().is_false())
return false;
if (lo[pos])
b = b.hi();
else
b = b.lo();
}
if (!contains(x, lo))
return false;
//
// find minimal index where b is false for some
@ -161,7 +190,7 @@ namespace dd {
unsigned idx = UINT_MAX;
vector<bdd> trail;
b = x;
bdd b = x;
for (unsigned i = lo.size(); i-- > 0; ) {
trail.push_back(b);
unsigned v = m_pos2var[i];
@ -181,8 +210,7 @@ namespace dd {
}
if (idx == UINT_MAX) {
// all values above lo satisfy x
for (auto& b : lo)
b = true;
reset(lo, true);
return true;
}
@ -205,19 +233,75 @@ namespace dd {
b = b.lo();
}
// subtract one from resulting vector:
for (auto& b : lo) {
b = !b;
if (!b)
break;
}
dec(lo);
return true;
}
bool fdd::inf(bdd const& b, bool_vector& hi) const {
bool fdd::inf(bdd const& x, bool_vector& hi) const {
SASSERT(hi.size() == num_bits());
return false;
if (!contains(x, hi))
return false;
// Let ub(x hi) be shorthand for "unbounded-below" of variable
// x with bit-string hi.
//
// we have the following identities:
// ub(_ []) = true
// ub(x 0 ++ hi) = lo(x) = T or ub(lo(x), hi)
// ub(x 1 ++ hi) = lo(x) = T and ub(hi(x), hi)
//
unsigned idx = UINT_MAX;
vector<bdd> trail;
bdd b = x;
for (unsigned i = hi.size(); i-- > 0; ) {
trail.push_back(b);
unsigned v = m_pos2var[i];
bdd nw = m->mk_nvar(v);
bdd lo = b.cofactor(nw);
if (!hi[i]) {
if (lo.is_true())
break;
SASSERT(!lo.is_false());
b = lo;
}
else {
if (!lo.is_true())
idx = i;
b = b.cofactor(m->mk_var(v));
}
}
if (idx == UINT_MAX) {
// all values below hi satisfy x
reset(hi, false);
return true;
}
SASSERT(hi[idx]);
trail.reverse();
hi[idx] = false;
unsigned v = m_pos2var[idx];
b = trail[idx].cofactor(m->mk_nvar(v));
// Check logic, TBD
for (unsigned i = idx; i-- > 0; ) {
SASSERT(!b.is_true());
if (b.is_false()) {
for (unsigned j = 0; j <= i; ++j)
hi[j] = true;
break;
}
hi[i] = b.lo().is_true();
if (hi[i])
b = b.hi();
else
b = b.lo();
}
inc(hi);
return true;
}

2
src/math/dd/dd_fdd.h
View file

@ -45,6 +45,8 @@ namespace dd {
unsigned var2pos(unsigned var) const;
bool contains(bdd const& b, bool_vector const& value) const;
public:
/** Initialize FDD using BDD variables from 0 to num_bits-1. */
fdd(bdd_manager& manager, unsigned num_bits, unsigned start = 0, unsigned step = 1) : fdd(manager, seq(num_bits, start, step)) { }