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Z3str3: Add consistency checks for string-integer conversion terms in model construction (#4551)

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* z3str3: check consistency of str.to_int in fixed length solver

* z3str3: add similar check for int.to_str as well

* z3str3: refactor string-integer conversion check and add post checks for model construction
This commit is contained in:
Murphy Berzish 2020-06-30 11:20:44 -05:00 • committed by GitHub
parent 8fda4f904d
commit fce1252145
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3 changed files with 199 additions and 35 deletions
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62
src/smt/theory_str.cpp
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@ -8134,6 +8134,31 @@ namespace smt {
return 0;
}
// Attempts to convert a string to a non-negative integer.
// Returns true if this can be done in a valid way, placing the converted value in the argument.
// Otherwise, returns false, if str is empty or contains non-digit characters.
bool theory_str::string_integer_conversion_valid(zstring str, rational& converted) const {
bool valid = true;
converted = rational::zero();
rational ten(10);
if (str.length() == 0) {
return false;
} else {
for (unsigned i = 0; i < str.length(); ++i) {
if (!('0' <= str[i] && str[i] <= '9')) {
return false;
} else {
// accumulate
char digit = (int)str[i];
std::string sDigit(1, digit);
int val = atoi(sDigit.c_str());
converted = (ten * converted) + rational(val);
}
}
return true;
}
}
// Check agreement between integer and string theories for the term a = (str.to-int S).
// Returns true if axioms were added, and false otherwise.
bool theory_str::finalcheck_str2int(app * a) {
@ -8189,27 +8214,9 @@ namespace smt {
if (S_hasEqcValue) {
zstring str;
u.str.is_string(S_str, str);
bool valid = true;
rational convertedRepresentation(0);
rational ten(10);
if (str.length() == 0) {
valid = false;
} else {
for (unsigned i = 0; i < str.length(); ++i) {
if (!('0' <= str[i] && str[i] <= '9')) {
valid = false;
break;
} else {
// accumulate
char digit = (int)str[i];
std::string sDigit(1, digit);
int val = atoi(sDigit.c_str());
convertedRepresentation = (ten * convertedRepresentation) + rational(val);
}
}
}
// TODO this duplicates code a bit, we can simplify the branch on "conclusion" only
if (valid) {
if (string_integer_conversion_valid(str, convertedRepresentation)) {
expr_ref premise(ctx.mk_eq_atom(S, mk_string(str)), m);
expr_ref conclusion(ctx.mk_eq_atom(a, m_autil.mk_numeral(convertedRepresentation, true)), m);
expr_ref axiom(rewrite_implication(premise, conclusion), m);
@ -8263,22 +8270,7 @@ namespace smt {
}
// nonempty string --> convert to correct integer value, or disallow it
rational convertedRepresentation(0);
rational ten(10);
bool conversionOK = true;
for (unsigned i = 0; i < Sval.length(); ++i) {
char digit = (int)Sval[i];
if (isdigit((int)digit)) {
std::string sDigit(1, digit);
int val = atoi(sDigit.c_str());
convertedRepresentation = (ten * convertedRepresentation) + rational(val);
} else {
// not a digit, invalid
TRACE("str", tout << "str.from-int argument contains non-digit character '" << digit << "'" << std::endl;);
conversionOK = false;
break;
}
}
if (conversionOK) {
if (string_integer_conversion_valid(Sval, convertedRepresentation)) {
expr_ref premise(ctx.mk_eq_atom(a, mk_string(Sval)), m);
expr_ref conclusion(ctx.mk_eq_atom(N, m_autil.mk_numeral(convertedRepresentation, true)), m);
expr_ref axiom(rewrite_implication(premise, conclusion), m);