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Merge branch 'unstable' of https://git01.codeplex.com/z3 into unstable

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Leonardo de Moura 2012-12-03 09:37:57 -08:00
parent b219b875b1 67485b8af7
commit 8744b26d06
9 changed files with 377 additions and 56 deletions
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33
src/muz_qe/equiv_proof_converter.cpp Normal file
View file

@ -0,0 +1,33 @@
/*++
Copyright (c) 2012 Microsoft Corporation
Module Name:
equiv_proof_converter.cpp
Abstract:
Proof converter that applies equivalence rule to leaves.
Author:
Nikolaj Bjorner (nbjorner) 2012-11-23
Revision History:
--*/
#include "equiv_proof_converter.h"
#include "ast_pp.h"
#include "dl_util.h"
void equiv_proof_converter::insert(expr* fml1, expr* fml2) {
datalog::scoped_fine_proof _sp(m);
proof_ref p1(m), p2(m), p3(m);
p1 = m.mk_asserted(fml1);
p2 = m.mk_rewrite(fml1, fml2);
p3 = m.mk_modus_ponens(p1, p2);
TRACE("proof_converter", tout << mk_pp(p3.get(), m) << "\n";);
SASSERT(m.has_fact(p3));
m_replace.insert(p3);
}

8
src/muz_qe/equiv_proof_converter.h
View file

@ -43,13 +43,7 @@ public:
return m_replace.translate(translator);
}
void insert(expr* fml1, expr* fml2) {
proof_ref p1(m), p2(m), p3(m);
p1 = m.mk_asserted(fml1);
p2 = m.mk_rewrite(fml1, fml2);
p3 = m.mk_modus_ponens(p1, p2);
m_replace.insert(p3);
}
void insert(expr* fml1, expr* fml2);
ast_manager& get_manager() { return m; }

78
src/muz_qe/pdr_context.cpp
View file

@ -162,9 +162,6 @@ namespace pdr {
}
}
void pred_transformer::find_predecessors(model_core const& model, ptr_vector<func_decl>& preds) const {
find_predecessors(find_rule(model), preds);
}
void pred_transformer::remove_predecessors(expr_ref_vector& literals) {
// remove tags
@ -740,6 +737,44 @@ namespace pdr {
return expr_ref(m.mk_app(f, args.size(), args.c_ptr()), m);
}
static bool is_ini(datalog::rule const& r) {
return r.get_uninterpreted_tail_size() == 0;
}
datalog::rule* model_node::get_rule() {
if (m_rule) {
return const_cast<datalog::rule*>(m_rule);
}
// only initial states are not set by the PDR search.
datalog::rule const& rl1 = pt().find_rule(*m_model);
if (is_ini(rl1)) {
set_rule(&rl1);
return const_cast<datalog::rule*>(m_rule);
}
ast_manager& m = pt().get_manager();
// otherwise, the initial state is reachable.
ptr_vector<datalog::rule> const& rules = pt().rules();
ptr_vector<datalog::rule> ini_rules;
expr_ref_vector tags(m);
expr_ref ini_tags(m), ini_state(m);
for (unsigned i = 0; i < rules.size(); ++i) {
datalog::rule* rl = rules[i];
if (is_ini(*rl)) {
tags.push_back(pt().rule2tag(rl));
}
}
SASSERT(!tags.empty());
ini_tags = m.mk_or(tags.size(), tags.c_ptr());
ini_state = m.mk_and(ini_tags, pt().initial_state(), state());
model_ref mdl;
pt().get_solver().set_model(&mdl);
VERIFY(l_true == pt().get_solver().check_conjunction_as_assumptions(ini_state));
datalog::rule const& rl2 = pt().find_rule(*mdl);
SASSERT(is_ini(rl2));
set_rule(&rl2);
return const_cast<datalog::rule*>(m_rule);
}
void model_node::mk_instantiate(datalog::rule_ref& r0, datalog::rule_ref& r1, expr_ref_vector& binding) {
ast_manager& m = pt().get_manager();
@ -763,7 +798,7 @@ namespace pdr {
model.insert(e, m.mk_true());
}
}
r0 = const_cast<datalog::rule*>(&pt().find_rule(*m_model.get()));
r0 = get_rule();
app_ref_vector& inst = pt().get_inst(r0);
TRACE("pdr", tout << mk_pp(state(), m) << " instance: " << inst.size() << "\n";);
for (unsigned i = 0; i < inst.size(); ++i) {
@ -1644,7 +1679,7 @@ namespace pdr {
switch (expand_state(n, cube, uses_level)) {
case l_true:
if (n.level() == 0) {
TRACE("pdr", tout << "reachable\n";);
TRACE("pdr", tout << "reachable at level 0\n";);
close_node(n);
}
else {
@ -1772,11 +1807,14 @@ namespace pdr {
expr* T = pt.get_transition(r);
expr* phi = n.state();
IF_VERBOSE(3, verbose_stream() << "Model:\n";
model_smt2_pp(verbose_stream(), m, *M, 0);
verbose_stream() << "\n";
verbose_stream() << "Transition:\n" << mk_pp(T, m) << "\n";
verbose_stream() << "Phi:\n" << mk_pp(phi, m) << "\n";);
n.set_rule(&r);
TRACE("pdr",
tout << "Model:\n";
model_smt2_pp(tout, m, *M, 0);
tout << "\n";
tout << "Transition:\n" << mk_pp(T, m) << "\n";
tout << "Phi:\n" << mk_pp(phi, m) << "\n";);
model_evaluator mev(m);
expr_ref_vector mdl(m), forms(m), Phi(m);
@ -1806,19 +1844,21 @@ namespace pdr {
qe_lite qe(m);
expr_ref phi1 = m_pm.mk_and(Phi);
qe(vars, phi1);
TRACE("pdr", tout << "Eliminated\n" << mk_pp(phi1, m) << "\n";);
if (!use_model_generalizer) {
reduce_disequalities(*M, 3, phi1);
TRACE("pdr", tout << "Reduced-eq\n" << mk_pp(phi1, m) << "\n";);
}
get_context().get_rewriter()(phi1);
IF_VERBOSE(2,
verbose_stream() << "Vars:\n";
for (unsigned i = 0; i < vars.size(); ++i) {
verbose_stream() << mk_pp(vars[i].get(), m) << "\n";
}
verbose_stream() << "Literals\n";
verbose_stream() << mk_pp(m_pm.mk_and(Phi), m) << "\n";
verbose_stream() << "Reduced\n" << mk_pp(phi1, m) << "\n";);
TRACE("pdr",
tout << "Vars:\n";
for (unsigned i = 0; i < vars.size(); ++i) {
tout << mk_pp(vars[i].get(), m) << "\n";
}
tout << "Literals\n";
tout << mk_pp(m_pm.mk_and(Phi), m) << "\n";
tout << "Reduced\n" << mk_pp(phi1, m) << "\n";);
if (!vars.empty()) {
// also fresh names for auxiliary variables in body?
@ -1833,7 +1873,7 @@ namespace pdr {
if (!rep) rep = mk_expr_simp_replacer(m);
rep->set_substitution(&sub);
(*rep)(phi1);
IF_VERBOSE(2, verbose_stream() << "Projected:\n" << mk_pp(phi1, m) << "\n";);
TRACE("pdr", tout << "Projected:\n" << mk_pp(phi1, m) << "\n";);
}
Phi.reset();
datalog::flatten_and(phi1, Phi);

9
src/muz_qe/pdr_context.h
View file

@ -132,7 +132,6 @@ namespace pdr {
bool is_reachable(expr* state);
void remove_predecessors(expr_ref_vector& literals);
void find_predecessors(datalog::rule const& r, ptr_vector<func_decl>& predicates) const;
void find_predecessors(model_core const& model, ptr_vector<func_decl>& preds) const;
datalog::rule const& find_rule(model_core const& model) const;
expr* get_transition(datalog::rule const& r) { return m_rule2transition.find(&r); }
ptr_vector<app>& get_aux_vars(datalog::rule const& r) { return m_rule2vars.find(&r); }
@ -163,6 +162,8 @@ namespace pdr {
void ground_free_vars(expr* e, app_ref_vector& vars, ptr_vector<app>& aux_vars);
prop_solver& get_solver() { return m_solver; }
};
@ -177,10 +178,11 @@ namespace pdr {
unsigned m_orig_level;
unsigned m_depth;
bool m_closed;
datalog::rule const* m_rule;
public:
model_node(model_node* parent, expr_ref& state, pred_transformer& pt, unsigned level):
m_parent(parent), m_pt(pt), m_state(state), m_model(0),
m_level(level), m_orig_level(level), m_depth(0), m_closed(false) {
m_level(level), m_orig_level(level), m_depth(0), m_closed(false), m_rule(0) {
if (m_parent) {
m_parent->m_children.push_back(this);
SASSERT(m_parent->m_level == level+1);
@ -217,6 +219,9 @@ namespace pdr {
void set_pre_closed() { m_closed = true; }
void reset() { m_children.reset(); }
void set_rule(datalog::rule const* r) { m_rule = r; }
datalog::rule* get_rule();
expr_ref get_trace() const;
void mk_instantiate(datalog::rule_ref& r0, datalog::rule_ref& r1, expr_ref_vector& binding);

37
src/muz_qe/pdr_quantifiers.cpp
View file

@ -105,7 +105,11 @@ namespace pdr {
}
void quantifier_model_checker::add_binding(quantifier* q, expr_ref_vector& binding) {
void quantifier_model_checker::add_binding(quantifier* q, expr_ref_vector& binding) {
if (binding.size() != q->get_num_decls()) {
// not a full binding. It may happen that the quantifier got simplified.
return;
}
apply_binding(q, binding);
vector<expr_ref_vector> bindings;
generalize_binding(binding, bindings);
@ -126,15 +130,18 @@ namespace pdr {
inst.append(var_inst.size(), (expr*const*)var_inst.c_ptr());
inst.reverse();
expr_abstract(m, 0, inst.size(), inst.c_ptr(), e, e);
if (m_instantiations.contains(to_app(e))) {
return;
}
m_instantiated_rules.push_back(m_current_rule);
m_instantiations.push_back(to_app(e));
TRACE("pdr", tout << mk_pp(q, m) << "\n";
tout << "binding\n";
tout << "binding: ";
for (unsigned i = 0; i < binding.size(); ++i) {
tout << mk_pp(binding[i].get(), m) << " ";
}
tout << "\n";
tout << "inst\n";
tout << "inst: ";
for (unsigned i = 0; i < var_inst.size(); ++i) {
tout << mk_pp(var_inst[i].get(), m) << " ";
}
@ -361,6 +368,7 @@ namespace pdr {
scoped_ptr<expr_replacer> rep = mk_default_expr_replacer(m);
for (unsigned j = 0; j < qis.size(); ++j) {
q = qis[j].get();
SASSERT(is_forall(q));
app_ref_vector& inst = pt.get_inst(m_current_rule);
TRACE("pdr",
tout << "q:\n" << mk_pp(q, m) << "\n";
@ -433,11 +441,16 @@ namespace pdr {
unsigned t_size = r.get_tail_size();
var_subst vs(m, false);
sort_ref_vector vars(m);
uint_set empty_index_set;
qe_lite qe(m);
r.get_vars(vars);
#if 1
if (qis) {
quantifier_ref_vector const& qi = *qis;
for (unsigned i = 0; i < qi.size(); ++i) {
fml = qi[i]->get_expr();
quantifier* q = qi[i];
fml = q->get_expr();
a = to_app(fml);
p = a->get_decl();
expr* p_reach = get_reachable(p);
@ -448,9 +461,17 @@ namespace pdr {
sub.insert(v, a->get_arg(j));
}
sub(p_reach, fml);
body.push_back(m.update_quantifier(qi[i], fml));
uint_set is;
for (unsigned j = 0; j < q->get_num_decls(); ++j) {
is.insert(j);
}
fml = m.mk_not(fml);
qe(is, true, fml);
fml = m.mk_not(fml);
body.push_back(m.update_quantifier(q, fml));
}
}
#endif
a = r.get_head();
for (unsigned i = 0; i < a->get_num_args(); ++i) {
v = m.mk_var(vars.size()+i, m.get_sort(a->get_arg(i)));
@ -489,8 +510,6 @@ namespace pdr {
SASSERT(is_well_sorted(m, fml));
if (!vars.empty()) {
fml = to_quantifier(fml)->get_expr();
uint_set empty_index_set;
qe_lite qe(m);
qe(empty_index_set, false, fml);
fml = m.mk_exists(vars.size(), vars.c_ptr(), names.c_ptr(), fml);
SASSERT(is_well_sorted(m, fml));
@ -498,7 +517,7 @@ namespace pdr {
}
SASSERT(is_well_sorted(m, fml));
IF_VERBOSE(0, verbose_stream() << "instantiate to\n:" << mk_pp(fml, m) << "\n";);
IF_VERBOSE(0, verbose_stream() << "instantiate to:\n" << mk_pp(fml, m) << "\n";);
return fml;
}
@ -517,7 +536,7 @@ namespace pdr {
if (!node.get_model_ptr()) {
return;
}
m_current_rule = &pt.find_rule(node.get_model());
m_current_rule = node.get_rule();
m_current_pt = &pt;
m_current_node = &node;
if (!m_current_rule) {

23
src/muz_qe/pdr_util.cpp
View file

@ -238,11 +238,13 @@ namespace pdr {
result.push_back(m.mk_not(e));
}
}
#if 0
select_elim_star select_elim(m, m_model);
for (unsigned i = 0; i < result.size(); ++i) {
select_elim(result[i].get(), tmp);
result[i] = tmp;
}
#endif
reset();
TRACE("pdr",
tout << "minimized model:\n";
@ -386,13 +388,12 @@ namespace pdr {
for_each_expr(*this, m_visited, tocollect[i]);
}
unsigned sz = m_model->get_num_constants();
expr_ref e(m), eq(m);
expr_ref e(m), eq(m), val(m);
expr_ref_vector model(m);
for (unsigned i = 0; i < sz; i++) {
func_decl * d = m_model->get_constant(i);
expr* val = m_model->get_const_interp(d);
e = m.mk_const(d);
e = m.mk_const(m_model->get_constant(i));
if (m_visited.is_marked(e)) {
val = eval(m_model, e);
eq = m.mk_eq(e, val);
model.push_back(eq);
}
@ -923,6 +924,20 @@ namespace pdr {
return !has_x;
}
expr_ref model_evaluator::eval(model_ref& model, func_decl* d) {
SASSERT(d->get_arity() == 0);
expr_ref result(m);
if (m_array.is_array(d->get_range())) {
expr_ref e(m);
e = m.mk_const(d);
result = eval(model, e);
}
else {
result = model->get_const_interp(d);
}
return result;
}
expr_ref model_evaluator::eval(model_ref& model, expr* e) {
expr_ref result(m);
m_model = model;

2
src/muz_qe/pdr_util.h
View file

@ -129,6 +129,8 @@ namespace pdr {
void operator()(expr* e) {}
expr_ref eval(model_ref& mdl, expr* e);
expr_ref eval(model_ref& mdl, func_decl* d);
};
/**

241
src/muz_qe/qe_lite.cpp
View file

@ -33,6 +33,8 @@ Revision History:
#include "dl_util.h"
#include "th_rewriter.h"
#include "dl_util.h"
#include "for_each_expr.h"
#include "expr_safe_replace.h"
class is_variable_proc {
@ -77,9 +79,10 @@ public:
namespace eq {
class der {
ast_manager & m;
arith_util a;
is_variable_proc* m_is_variable;
var_subst m_subst;
expr_ref_buffer m_new_exprs;
expr_ref_vector m_new_exprs;
ptr_vector<expr> m_map;
int_vector m_pos2var;
@ -225,7 +228,81 @@ namespace eq {
return false;
}
}
bool solve_arith_core(app * lhs, expr * rhs, expr * eq, var* & var, expr_ref & def) {
SASSERT(a.is_add(lhs));
bool is_int = a.is_int(lhs);
expr * a1;
expr * v;
rational a_val;
unsigned num = lhs->get_num_args();
unsigned i;
for (i = 0; i < num; i++) {
expr * arg = lhs->get_arg(i);
if (is_variable(arg)) {
a_val = rational(1);
v = arg;
break;
}
else if (a.is_mul(arg, a1, v) &&
is_variable(v) &&
a.is_numeral(a1, a_val) &&
!a_val.is_zero() &&
(!is_int || a_val.is_minus_one())) {
break;
}
}
if (i == num)
return false;
var = to_var(v);
expr_ref inv_a(m);
if (!a_val.is_one()) {
inv_a = a.mk_numeral(rational(1)/a_val, is_int);
rhs = a.mk_mul(inv_a, rhs);
}
ptr_buffer<expr> other_args;
for (unsigned j = 0; j < num; j++) {
if (i != j) {
if (inv_a)
other_args.push_back(a.mk_mul(inv_a, lhs->get_arg(j)));
else
other_args.push_back(lhs->get_arg(j));
}
}
switch (other_args.size()) {
case 0:
def = rhs;
break;
case 1:
def = a.mk_sub(rhs, other_args[0]);
break;
default:
def = a.mk_sub(rhs, a.mk_add(other_args.size(), other_args.c_ptr()));
break;
}
m_new_exprs.push_back(def);
return true;
}
bool arith_solve(expr * lhs, expr * rhs, expr * eq, var* & var, expr_ref & t) {
return
(a.is_add(lhs) && solve_arith_core(to_app(lhs), rhs, eq, var, t)) ||
(a.is_add(rhs) && solve_arith_core(to_app(rhs), lhs, eq, var, t));
}
bool trival_solve(expr* lhs, expr* rhs, expr* eq, var* & v, expr_ref& t) {
if (!is_variable(lhs)) {
std::swap(lhs, rhs);
}
if (!is_variable(lhs)) {
return false;
}
v = to_var(lhs);
t = rhs;
TRACE("der", tout << mk_pp(eq, m) << "\n";);
return true;
}
/**
@ -251,14 +328,13 @@ namespace eq {
TRACE("der", tout << mk_pp(e, m) << "\n";);
return true;
}
if (!is_variable(lhs))
std::swap(lhs, rhs);
if (!is_variable(lhs))
return false;
v = to_var(lhs);
t = rhs;
TRACE("der", tout << mk_pp(e, m) << "\n";);
return true;
if (trival_solve(lhs, rhs, e, v, t)) {
return true;
}
if (arith_solve(lhs, rhs, e, v, t)) {
return true;
}
return false;
}
// (ite cond (= VAR t) (= VAR t2)) case
@ -494,7 +570,7 @@ namespace eq {
}
public:
der(ast_manager & m): m(m), m_is_variable(0), m_subst(m), m_new_exprs(m), m_subst_map(m), m_new_args(m), m_rewriter(m) {}
der(ast_manager & m): m(m), a(m), m_is_variable(0), m_subst(m), m_new_exprs(m), m_subst_map(m), m_new_args(m), m_rewriter(m) {}
void set_is_variable_proc(is_variable_proc& proc) { m_is_variable = &proc;}
@ -538,20 +614,129 @@ namespace eq {
namespace ar {
class der {
ast_manager& m;
array_util a;
is_variable_proc* m_is_variable;
ptr_vector<expr> m_todo;
expr_mark m_visited;
bool is_variable(expr * e) const {
return (*m_is_variable)(e);
}
void mark_all(expr* e) {
for_each_expr(*this, m_visited, e);
}
void mark_all(expr_ref_vector const& fmls, unsigned j) {
for (unsigned i = 0; i < fmls.size(); ++i) {
if (i != j) {
mark_all(fmls[i]);
}
}
}
/**
Ex A. A[x] = t & Phi where x \not\in A, t.
=>
Ex A. Phi[store(A,x,t)]
*/
bool solve_select(expr_ref_vector& conjs, unsigned i, expr* e1, expr* e2) {
if (a.is_select(e1)) {
app* a1 = to_app(e1);
expr* A = a1->get_arg(0);
if (!is_variable(A)) {
return false;
}
m_visited.reset();
for (unsigned j = 1; j < a1->get_num_args(); ++j) {
mark_all(a1->get_arg(j));
}
mark_all(e2);
if (m_visited.is_marked(A)) {
return false;
}
ptr_vector<expr> args;
args.push_back(A);
args.append(a1->get_num_args()-1, a1->get_args()+1);
args.push_back(e2);
expr* B = a.mk_store(args.size(), args.c_ptr());
expr_safe_replace rep(m);
rep.insert(A, B);
expr_ref tmp(m);
for (unsigned j = 0; j < conjs.size(); ++j) {
if (i == j) {
conjs[j] = m.mk_true();
}
else {
rep(conjs[j].get(), tmp);
conjs[j] = tmp;
}
}
return true;
}
return false;
}
bool solve_select(expr_ref_vector& conjs, unsigned i, expr* e) {
expr* e1, *e2;
return
m.is_eq(e, e1, e2) &&
(solve_select(conjs, i, e1, e2) ||
solve_select(conjs, i, e2, e1));
}
/**
Ex x. A[x] != B[x] & Phi where x \not\in A, B, Phi
=>
A != B & Phi
*/
bool solve_neq_select(expr_ref_vector& conjs, unsigned i, expr* e) {
expr* e1, *a1, *a2;
if (m.is_not(e, e1) && m.is_eq(e1, a1, a2)) {
if (a.is_select(a1) &&
a.is_select(a2) &&
to_app(a1)->get_num_args() == to_app(a2)->get_num_args()) {
expr* e1 = to_app(a1)->get_arg(0);
expr* e2 = to_app(a2)->get_arg(0);
m_visited.reset();
mark_all(conjs, i);
mark_all(e1);
mark_all(e2);
for (unsigned j = 1; j < to_app(a1)->get_num_args(); ++j) {
expr* x = to_app(a1)->get_arg(j);
expr* y = to_app(a2)->get_arg(j);
if (!is_variable(x)) {
return false;
}
if (x != y) {
return false;
}
if (m_visited.is_marked(x)) {
return false;
}
}
conjs[i] = m.mk_not(m.mk_eq(e1, e2));
return true;
}
}
return false;
}
public:
der(ast_manager& m): m(m), m_is_variable(0) {}
der(ast_manager& m): m(m), a(m), m_is_variable(0) {}
void operator()(expr_ref_vector& fmls) {
IF_VERBOSE(1, verbose_stream() << "Todo: eliminate arrays\n";);
for (unsigned i = 0; i < fmls.size(); ++i) {
solve_select(fmls, i, fmls[i].get());
solve_neq_select(fmls, i, fmls[i].get());
}
}
void operator()(expr* e) {}
void set_is_variable_proc(is_variable_proc& proc) { m_is_variable = &proc;}
};
@ -1904,6 +2089,22 @@ class qe_lite::impl {
fm::fm m_fm;
ar::der m_array_der;
bool has_unique_non_ground(expr_ref_vector const& fmls, unsigned& index) {
index = fmls.size();
if (index <= 1) {
return false;
}
for (unsigned i = 0; i < fmls.size(); ++i) {
if (!is_ground(fmls[i])) {
if (index != fmls.size()) {
return false;
}
index = i;
}
}
return index < fmls.size();
}
public:
impl(ast_manager& m): m(m), m_der(m), m_fm(m, m_params), m_array_der(m) {}
@ -1970,9 +2171,21 @@ public:
void operator()(uint_set const& index_set, bool index_of_bound, expr_ref_vector& fmls) {
datalog::flatten_and(fmls);
unsigned index;
if (has_unique_non_ground(fmls, index)) {
expr_ref fml(m);
fml = fmls[index].get();
(*this)(index_set, index_of_bound, fml);
fmls[index] = fml;
return;
}
TRACE("qe_lite", for (unsigned i = 0; i < fmls.size(); ++i) {
tout << mk_pp(fmls[i].get(), m) << "\n";
});
IF_VERBOSE(3, for (unsigned i = 0; i < fmls.size(); ++i) {
verbose_stream() << mk_pp(fmls[i].get(), m) << "\n";
});
is_variable_test is_var(index_set, index_of_bound);
TRACE("qe_lite", for (unsigned i = 0; i < fmls.size(); ++i) tout << mk_pp(fmls[i].get(), m) << "\n";);
IF_VERBOSE(3, for (unsigned i = 0; i < fmls.size(); ++i) verbose_stream() << mk_pp(fmls[i].get(), m) << "\n";);
m_der.set_is_variable_proc(is_var);
m_fm.set_is_variable_proc(is_var);
m_array_der.set_is_variable_proc(is_var);

2
src/tactic/fpa/fpa2bv_converter.cpp
View file

@ -1403,7 +1403,7 @@ void fpa2bv_converter::mk_to_ieee_bv(func_decl * f, unsigned num, expr * const *
SASSERT(num == 1);
expr * sgn, * s, * e;
split(args[0], sgn, s, e);
result = m_bv_util.mk_concat(m_bv_util.mk_concat(sgn, s), e);
result = m_bv_util.mk_concat(m_bv_util.mk_concat(sgn, e), s);
}
void fpa2bv_converter::split(expr * e, expr * & sgn, expr * & sig, expr * & exp) const {