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add alternate str.at semantics check in seq_rewriter

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this rewrites to empty string if the index is negative or beyond the length of the string,
which is consistent with CVC4's semantics for this term
This commit is contained in:
Murphy Berzish 2017-03-13 14:39:12 -04:00
parent 5a79722071
commit 5c9d7538a0
1 changed files with 15 additions and 4 deletions
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19
src/ast/rewriter/seq_rewriter.cpp
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@ -598,14 +598,25 @@ br_status seq_rewriter::mk_seq_contains(expr* a, expr* b, expr_ref& result) {
return BR_FAILED;
}
/*
* (str.at s i), constants s/i, i < 0 or i >= |s| ==> (str.at s i) = ""
*/
br_status seq_rewriter::mk_seq_at(expr* a, expr* b, expr_ref& result) {
zstring c;
rational r;
if (m_util.str.is_string(a, c) && m_autil.is_numeral(b, r) && r.is_unsigned()) {
unsigned j = r.get_unsigned();
if (j < c.length()) {
result = m_util.str.mk_string(c.extract(j, 1));
if (m_util.str.is_string(a, c) && m_autil.is_numeral(b, r)) {
if (r.is_neg()) {
result = m_util.str.mk_string(symbol(""));
return BR_DONE;
} else if (r.is_unsigned()) {
unsigned j = r.get_unsigned();
if (j < c.length()) {
result = m_util.str.mk_string(c.extract(j, 1));
return BR_DONE;
} else {
result = m_util.str.mk_string(symbol(""));
return BR_DONE;
}
}
}
return BR_FAILED;