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make semantics of extract/substr deterministic. Issue #781

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2016-11-15 18:29:51 +02:00
parent fa8427258a
commit e65d80dedd
1 changed files with 22 additions and 15 deletions
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37
src/smt/theory_seq.cpp
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@ -3259,15 +3259,18 @@ bool theory_seq::get_length(expr* e, rational& val) const {
let e = extract(s, i, l)
0 <= i <= len(s) -> prefix(xe,s)
0 <= i <= len(s) -> len(x) = i
0 <= i <= len(s) & 0 <= l <= len(s) - i -> len(e) = l
0 <= i <= len(s) & len(s) < l + i -> len(e) = len(s) - i
0 <= i <= len(s) & l < 0 -> len(e) = 0
* i < 0 -> e = empty
* i > len(s) -> e = empty
0 <= i <= |s| -> prefix(xe,s)
0 <= i <= |s| -> len(x) = i
0 <= i <= |s| & 0 <= l <= |s| - i -> |e| = l
0 <= i <= |s| & |s| < l + i -> |e| = |s| - i
0 <= i <= |s| & l < 0 -> |e| = 0
i >= |s| => |e| = 0
i < 0 => |e| = 0
l <= 0 => |e| = 0
It follows that:
|e| = min(l, |s| - i) for 0 <= i < |s| and 0 < |l|
*/
@ -3301,16 +3304,20 @@ void theory_seq::add_extract_axiom(expr* e) {
expr_ref zero(m_autil.mk_int(0), m);
literal i_ge_0 = mk_literal(m_autil.mk_ge(i, zero));
literal i_le_ls = mk_literal(m_autil.mk_le(mk_sub(i, ls), zero));
literal ls_le_i = mk_literal(m_autil.mk_le(mk_sub(i, ls), zero));
literal li_ge_ls = mk_literal(m_autil.mk_ge(ls_minus_i_l, zero));
literal l_ge_zero = mk_literal(m_autil.mk_ge(l, zero));
literal ls_le_0 = mk_literal(m_autil.mk_le(ls, zero));
// add_axiom(~i_ge_0, ~i_le_ls, mk_literal(m_util.str.mk_prefix(xe, s)));
add_axiom(~i_ge_0, ~i_le_ls, mk_seq_eq(xey, s));
add_axiom(~i_ge_0, ~i_le_ls, mk_eq(lx, i, false));
add_axiom(~i_ge_0, ~i_le_ls, ~l_ge_zero, ~li_ge_ls, mk_eq(le, l, false));
add_axiom(~i_ge_0, ~i_le_ls, li_ge_ls, mk_eq(le, mk_sub(ls, i), false));
add_axiom(~i_ge_0, ~i_le_ls, l_ge_zero, mk_eq(le, zero, false));
// add_axiom(~i_ge_0, ~ls_le_i, mk_literal(m_util.str.mk_prefix(xe, s)));
add_axiom(~i_ge_0, ~ls_le_i, mk_seq_eq(xey, s));
add_axiom(~i_ge_0, ~ls_le_i, mk_eq(lx, i, false));
add_axiom(~i_ge_0, ~ls_le_i, ~l_ge_zero, ~li_ge_ls, mk_eq(le, l, false));
add_axiom(~i_ge_0, ~ls_le_i, li_ge_ls, mk_eq(le, mk_sub(ls, i), false));
add_axiom(~i_ge_0, ~ls_le_i, l_ge_zero, mk_eq(le, zero, false));
add_axiom(i_ge_0, mk_eq(le, zero, false));
add_axiom(ls_le_i, mk_eq(le, zero, false));
add_axiom(~ls_le_0, mk_eq(le, zero, false));
}
void theory_seq::add_tail_axiom(expr* e, expr* s) {