solidity/libsolidity/analysis/ConstantEvaluator.cpp

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/*
This file is part of solidity.
solidity is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
solidity is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with solidity. If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
* @author Christian <c@ethdev.com>
* @date 2015
* Evaluator for types of constant expressions.
*/
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#include <libsolidity/analysis/ConstantEvaluator.h>
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#include <libsolidity/ast/AST.h>
#include <libsolidity/ast/TypeProvider.h>
#include <liblangutil/ErrorReporter.h>
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#include <limits>
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using namespace solidity;
using namespace solidity::frontend;
using namespace solidity::langutil;
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using TypedRational = ConstantEvaluator::TypedRational;
namespace
{
/// Check whether (_base ** _exp) fits into 4096 bits.
bool fitsPrecisionExp(bigint const& _base, bigint const& _exp)
{
if (_base == 0)
return true;
solAssert(_base > 0, "");
std::size_t const bitsMax = 4096;
std::size_t mostSignificantBaseBit = static_cast<std::size_t>(boost::multiprecision::msb(_base));
if (mostSignificantBaseBit == 0) // _base == 1
return true;
if (mostSignificantBaseBit > bitsMax) // _base >= 2 ^ 4096
return false;
bigint bitsNeeded = _exp * (mostSignificantBaseBit + 1);
return bitsNeeded <= bitsMax;
}
/// Checks whether _mantissa * (2 ** _expBase10) fits into 4096 bits.
bool fitsPrecisionBase2(bigint const& _mantissa, uint32_t _expBase2)
{
return fitsPrecisionBaseX(_mantissa, 1.0, _expBase2);
}
}
std::optional<rational> ConstantEvaluator::evaluateBinaryOperator(Token _operator, rational const& _left, rational const& _right)
{
bool fractional = _left.denominator() != 1 || _right.denominator() != 1;
switch (_operator)
{
//bit operations will only be enabled for integers and fixed types that resemble integers
case Token::BitOr:
if (fractional)
return std::nullopt;
else
return _left.numerator() | _right.numerator();
case Token::BitXor:
if (fractional)
return std::nullopt;
else
return _left.numerator() ^ _right.numerator();
case Token::BitAnd:
if (fractional)
return std::nullopt;
else
return _left.numerator() & _right.numerator();
case Token::Add: return _left + _right;
case Token::Sub: return _left - _right;
case Token::Mul: return _left * _right;
case Token::Div:
if (_right == rational(0))
return std::nullopt;
else
return _left / _right;
case Token::Mod:
if (_right == rational(0))
return std::nullopt;
else if (fractional)
{
rational tempValue = _left / _right;
return _left - (tempValue.numerator() / tempValue.denominator()) * _right;
}
else
return _left.numerator() % _right.numerator();
break;
case Token::Exp:
{
if (_right.denominator() != 1)
return std::nullopt;
bigint const& exp = _right.numerator();
// x ** 0 = 1
// for 0, 1 and -1 the size of the exponent doesn't have to be restricted
if (exp == 0)
return 1;
else if (_left == 0 || _left == 1)
return _left;
else if (_left == -1)
{
bigint isOdd = abs(exp) & bigint(1);
return 1 - 2 * isOdd.convert_to<int>();
}
else
{
if (abs(exp) > std::numeric_limits<uint32_t>::max())
return std::nullopt; // This will need too much memory to represent.
uint32_t absExp = bigint(abs(exp)).convert_to<uint32_t>();
if (!fitsPrecisionExp(abs(_left.numerator()), absExp) || !fitsPrecisionExp(abs(_left.denominator()), absExp))
return std::nullopt;
static auto const optimizedPow = [](bigint const& _base, uint32_t _exponent) -> bigint {
if (_base == 1)
return 1;
else if (_base == -1)
return 1 - 2 * static_cast<int>(_exponent & 1);
else
return boost::multiprecision::pow(_base, _exponent);
};
bigint numerator = optimizedPow(_left.numerator(), absExp);
bigint denominator = optimizedPow(_left.denominator(), absExp);
if (exp >= 0)
return makeRational(numerator, denominator);
else
// invert
return makeRational(denominator, numerator);
}
break;
}
case Token::SHL:
{
if (fractional)
return std::nullopt;
else if (_right < 0)
return std::nullopt;
else if (_right > std::numeric_limits<uint32_t>::max())
return std::nullopt;
if (_left.numerator() == 0)
return 0;
else
{
uint32_t exponent = _right.numerator().convert_to<uint32_t>();
if (!fitsPrecisionBase2(abs(_left.numerator()), exponent))
return std::nullopt;
return _left.numerator() * boost::multiprecision::pow(bigint(2), exponent);
}
break;
}
// NOTE: we're using >> (SAR) to denote right shifting. The type of the LValue
// determines the resulting type and the type of shift (SAR or SHR).
case Token::SAR:
{
if (fractional)
return std::nullopt;
else if (_right < 0)
return std::nullopt;
else if (_right > std::numeric_limits<uint32_t>::max())
return std::nullopt;
if (_left.numerator() == 0)
return 0;
else
{
uint32_t exponent = _right.numerator().convert_to<uint32_t>();
if (exponent > boost::multiprecision::msb(boost::multiprecision::abs(_left.numerator())))
return _left.numerator() < 0 ? -1 : 0;
else
{
if (_left.numerator() < 0)
// Add 1 to the negative value before dividing to get a result that is strictly too large,
// then subtract 1 afterwards to round towards negative infinity.
// This is the same algorithm as used in ExpressionCompiler::appendShiftOperatorCode(...).
// To see this note that for negative x, xor(x,all_ones) = (-x-1) and
// therefore xor(div(xor(x,all_ones), exp(2, shift_amount)), all_ones) is
// -(-x - 1) / 2^shift_amount - 1, which is the same as
// (x + 1) / 2^shift_amount - 1.
return rational((_left.numerator() + 1) / boost::multiprecision::pow(bigint(2), exponent) - bigint(1), 1);
else
return rational(_left.numerator() / boost::multiprecision::pow(bigint(2), exponent), 1);
}
}
break;
}
default:
return std::nullopt;
}
}
std::optional<rational> ConstantEvaluator::evaluateUnaryOperator(Token _operator, rational const& _input)
{
switch (_operator)
{
case Token::BitNot:
if (_input.denominator() != 1)
return std::nullopt;
else
return ~_input.numerator();
case Token::Sub:
return -_input;
default:
return std::nullopt;
}
}
namespace
{
std::optional<TypedRational> convertType(rational const& _value, Type const& _type)
{
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if (_type.category() == Type::Category::RationalNumber)
return TypedRational{TypeProvider::rationalNumber(_value), _value};
else if (auto const* integerType = dynamic_cast<IntegerType const*>(&_type))
{
if (_value > integerType->maxValue() || _value < integerType->minValue())
return std::nullopt;
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else
return TypedRational{&_type, _value.numerator() / _value.denominator()};
}
else
return std::nullopt;
}
std::optional<TypedRational> convertType(std::optional<TypedRational> const& _value, Type const& _type)
{
return _value ? convertType(_value->value, _type) : std::nullopt;
}
std::optional<TypedRational> constantToTypedValue(Type const& _type)
{
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if (_type.category() == Type::Category::RationalNumber)
return TypedRational{&_type, dynamic_cast<RationalNumberType const&>(_type).value()};
else
return std::nullopt;
}
}
std::optional<TypedRational> ConstantEvaluator::evaluate(
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langutil::ErrorReporter& _errorReporter,
Expression const& _expr
)
{
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return ConstantEvaluator{_errorReporter}.evaluate(_expr);
}
std::optional<TypedRational> ConstantEvaluator::evaluate(ASTNode const& _node)
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{
if (!m_values.count(&_node))
{
if (auto const* varDecl = dynamic_cast<VariableDeclaration const*>(&_node))
{
solAssert(varDecl->isConstant(), "");
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// In some circumstances, we do not yet have a type for the variable.
if (!varDecl->value() || !varDecl->type())
m_values[&_node] = std::nullopt;
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else
{
m_depth++;
if (m_depth > 32)
m_errorReporter.fatalTypeError(
5210_error,
varDecl->location(),
"Cyclic constant definition (or maximum recursion depth exhausted)."
);
m_values[&_node] = convertType(evaluate(*varDecl->value()), *varDecl->type());
m_depth--;
}
}
else if (auto const* expression = dynamic_cast<Expression const*>(&_node))
{
expression->accept(*this);
if (!m_values.count(&_node))
m_values[&_node] = std::nullopt;
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}
}
return m_values.at(&_node);
}
void ConstantEvaluator::endVisit(UnaryOperation const& _operation)
{
std::optional<TypedRational> value = evaluate(_operation.subExpression());
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if (!value)
return;
Type const* resultType = value->type->unaryOperatorResult(_operation.getOperator());
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if (!resultType)
return;
value = convertType(value, *resultType);
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if (!value)
return;
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if (std::optional<rational> result = evaluateUnaryOperator(_operation.getOperator(), value->value))
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{
std::optional<TypedRational> convertedValue = convertType(*result, *resultType);
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if (!convertedValue)
m_errorReporter.fatalTypeError(
3667_error,
_operation.location(),
"Arithmetic error when computing constant value."
);
m_values[&_operation] = convertedValue;
}
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}
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void ConstantEvaluator::endVisit(BinaryOperation const& _operation)
{
std::optional<TypedRational> left = evaluate(_operation.leftExpression());
std::optional<TypedRational> right = evaluate(_operation.rightExpression());
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if (!left || !right)
return;
// If this is implemented in the future: Comparison operators have a "binaryOperatorResult"
// that is non-bool, but the result has to be bool.
if (TokenTraits::isCompareOp(_operation.getOperator()))
return;
Type const* resultType = left->type->binaryOperatorResult(_operation.getOperator(), right->type);
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if (!resultType)
{
m_errorReporter.fatalTypeError(
6020_error,
_operation.location(),
"Operator " +
std::string(TokenTraits::toString(_operation.getOperator())) +
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" not compatible with types " +
left->type->toString() +
" and " +
right->type->toString()
);
return;
}
left = convertType(left, *resultType);
right = convertType(right, *resultType);
if (!left || !right)
return;
if (std::optional<rational> value = evaluateBinaryOperator(_operation.getOperator(), left->value, right->value))
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{
std::optional<TypedRational> convertedValue = convertType(*value, *resultType);
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if (!convertedValue)
m_errorReporter.fatalTypeError(
2643_error,
_operation.location(),
"Arithmetic error when computing constant value."
);
m_values[&_operation] = convertedValue;
}
}
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void ConstantEvaluator::endVisit(Literal const& _literal)
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{
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if (Type const* literalType = TypeProvider::forLiteral(_literal))
m_values[&_literal] = constantToTypedValue(*literalType);
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}
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void ConstantEvaluator::endVisit(Identifier const& _identifier)
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{
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VariableDeclaration const* variableDeclaration = dynamic_cast<VariableDeclaration const*>(_identifier.annotation().referencedDeclaration);
if (variableDeclaration && variableDeclaration->isConstant())
m_values[&_identifier] = evaluate(*variableDeclaration);
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}
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void ConstantEvaluator::endVisit(TupleExpression const& _tuple)
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{
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if (!_tuple.isInlineArray() && _tuple.components().size() == 1)
m_values[&_tuple] = evaluate(*_tuple.components().front());
}