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Fix conversion from bytes to fixed bytes

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This commit is contained in:
Leo Alt
2021-06-01 17:55:18 +02:00
parent 547a6915ad
commit bf21cd400c
5 changed files with 64 additions and 0 deletions
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libsolidity/formal/SMTEncoder.cpp
+30
View File
@@ -1022,6 +1022,17 @@ void SMTEncoder::visitTypeConversion(FunctionCall const& _funCall)
return;
}
ArrayType const* arrayType = dynamic_cast<ArrayType const*>(argType);
if (auto sliceType = dynamic_cast<ArraySliceType const*>(argType))
arrayType = &sliceType->arrayType();
if (arrayType && arrayType->isByteArray() && smt::isFixedBytes(*funCallType))
{
auto array = dynamic_pointer_cast<smt::SymbolicArrayVariable>(m_context.expression(*argument));
bytesToFixedBytesAssertions(*array, _funCall);
return;
}
// TODO Simplify this whole thing for 0.8.0 where weird casts are disallowed.
unsigned argSize = argType->storageBytes();
@@ -1206,6 +1217,25 @@ void SMTEncoder::addArrayLiteralAssertions(
m_context.addAssertion(smtutil::Expression::select(_symArray.elements(), i) == _elementValues[i]);
}
void SMTEncoder::bytesToFixedBytesAssertions(
smt::SymbolicArrayVariable& _symArray,
Expression const& _fixedBytes
)
{
auto const& fixed = dynamic_cast<FixedBytesType const&>(*_fixedBytes.annotation().type);
auto intType = TypeProvider::uint256();
string suffix = to_string(_fixedBytes.id()) + "_" + to_string(m_context.newUniqueId());
smt::SymbolicIntVariable k(intType, intType, "k_" + suffix, m_context);
m_context.addAssertion(k.currentValue() == 0);
size_t n = fixed.numBytes();
for (size_t i = 0; i < n; i++)
{
auto kPrev = k.currentValue();
m_context.addAssertion((smtutil::Expression::select(_symArray.elements(), i) * (u256(1) << ((n - i - 1) * 8))) + kPrev == k.increaseIndex());
}
m_context.addAssertion(expr(_fixedBytes) == k.currentValue());
}
void SMTEncoder::endVisit(Return const& _return)
{
if (_return.expression() && m_context.knownExpression(*_return.expression()))
libsolidity/formal/SMTEncoder.h
+5
View File
@@ -245,6 +245,11 @@ protected:
std::vector<smtutil::Expression> const& _elementValues
);
void bytesToFixedBytesAssertions(
smt::SymbolicArrayVariable& _symArray,
Expression const& _fixedBytes
);
/// @returns a pair of expressions representing _left / _right and _left mod _right, respectively.
/// Uses slack variables and additional constraints to express the results using only operations
/// more friendly to the SMT solver (multiplication, addition, subtraction and comparison).