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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2021-02-18 13:46:59 -08:00
parent 00dab30ea0
commit ca9fcbd1df
3 changed files with 37 additions and 1 deletions
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4
src/ast/rewriter/seq_axioms.cpp
View file

@ -139,10 +139,12 @@ namespace seq {
extract_prefix_axiom(e, s, l);
return;
}
#if 0
if (is_extract_suffix(s, _i, _l)) {
extract_suffix_axiom(e, i, l);
extract_suffix_axiom(e, s, i);
return;
}
#endif
TRACE("seq", tout << s << " " << i << " " << l << "\n";);
expr_ref x = m_sk.mk_pre(s, i);
expr_ref ls = mk_len(_s);

32
src/smt/seq_axioms.cpp
View file

@ -128,6 +128,10 @@ void seq_axioms::add_extract_axiom(expr* e) {
add_extract_prefix_axiom(e, s, l);
return;
}
if (is_extract_suffix(s, i, l)) {
add_extract_suffix_axiom(e, s, i);
return;
}
expr_ref x = m_sk.mk_pre(s, i);
expr_ref ls = mk_len(s);
expr_ref lx = mk_len(x);
@ -213,6 +217,12 @@ bool seq_axioms::is_extract_prefix0(expr* s, expr* i, expr* l) {
return a.is_numeral(i, i1) && i1.is_zero();
}
bool seq_axioms::is_extract_suffix(expr* s, expr* i, expr* l) {
expr_ref len(a.mk_add(l, i), m);
m_rewrite(len);
return seq.str.is_length(len, l) && l == s;
}
/*
s = ey
@ -235,6 +245,28 @@ void seq_axioms::add_extract_prefix_axiom(expr* e, expr* s, expr* l) {
}
/*
s = xe
0 <= i <= len(s) => i = len(x)
i < 0 => e = empty
i > len(s) => e = empty
*/
void seq_axioms::add_extract_suffix_axiom(expr* e, expr* s, expr* i) {
TRACE("seq", tout << "suffix " << mk_bounded_pp(e, m, 2) << " " << mk_bounded_pp(s, m, 2) << "\n";);
expr_ref x = m_sk.mk_pre(s, i);
expr_ref lx = mk_len(x);
expr_ref ls = mk_len(s);
expr_ref xe = mk_concat(x, e);
literal emp = mk_eq_empty(e);
literal i_ge_0 = mk_ge(i, 0);
literal i_le_s = mk_le(mk_sub(i, ls), 0);
add_axiom(mk_eq(s, xe));
add_axiom(~i_ge_0, ~i_le_s, mk_eq(i, lx));
add_axiom(i_ge_0, emp);
add_axiom(i_le_s, emp);
}
/*
encode that s is not contained in of xs1
where s1 is all of s, except the last element.

2
src/smt/seq_axioms.h
View file

@ -60,7 +60,9 @@ namespace smt {
bool is_drop_last(expr* s, expr* i, expr* l);
bool is_tail(expr* s, expr* i, expr* l);
bool is_extract_prefix0(expr* s, expr* i, expr* l);
bool is_extract_suffix(expr* s, expr* i, expr* l);
void add_extract_prefix_axiom(expr* e, expr* s, expr* l);
void add_extract_suffix_axiom(expr* e, expr* s, expr* i);
void tightest_prefix(expr* s, expr* x);
void ensure_digit_axiom();
void add_clause(expr_ref_vector const& lits);