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/*
This file is part of cpp-ethereum.
cpp-ethereum 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.
cpp-ethereum 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 cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
*/
/** @file GasMeter.cpp
* @author Christian <c@ethdev.com>
* @date 2015
*/
#pragma once
#include <ostream>
#include <tuple>
#include <libevmasm/ExpressionClasses.h>
#include <libevmasm/AssemblyItem.h>
#include <libethcore/ChainOperationParams.h>
namespace dev
{
namespace eth
{
class KnownState;
// TODO: FIXME: HOMESTEAD: XXX: @chfast populate m_schedule from an ExtVMFace instance via ExtVMFace::evmSchedule.
/**
* Class that helps computing the maximum gas consumption for instructions.
* Has to be initialized with a certain known state that will be automatically updated for
* each call to estimateMax. These calls have to supply strictly subsequent AssemblyItems.
* A new gas meter has to be constructed (with a new state) for control flow changes.
*/
class GasMeter
{
public:
struct GasConsumption
{
GasConsumption(u256 _value = 0, bool _infinite = false): value(_value), isInfinite(_infinite) {}
static GasConsumption infinite() { return GasConsumption(0, true); }
GasConsumption& operator+=(GasConsumption const& _other);
bool operator<(GasConsumption const& _other) const { return this->tuple() < _other.tuple(); }
std::tuple<bool const&, u256 const&> tuple() const { return std::tie(isInfinite, value); }
u256 value;
bool isInfinite;
};
/// Constructs a new gas meter given the current state.
explicit GasMeter(std::shared_ptr<KnownState> const& _state, u256 const& _largestMemoryAccess = 0):
m_state(_state), m_largestMemoryAccess(_largestMemoryAccess) {}
/// @returns an upper bound on the gas consumed by the given instruction and updates
/// the state.
GasConsumption estimateMax(AssemblyItem const& _item);
u256 const& largestMemoryAccess() const { return m_largestMemoryAccess; }
u256 runGas(Instruction _instruction) const { return runGas(_instruction, m_schedule); }
static u256 runGas(Instruction _instruction, EVMSchedule const& _es);
private:
/// @returns _multiplier * (_value + 31) / 32, if _value is a known constant and infinite otherwise.
GasConsumption wordGas(u256 const& _multiplier, ExpressionClasses::Id _value);
/// @returns the gas needed to access the given memory position.
/// @todo this assumes that memory was never accessed before and thus over-estimates gas usage.
GasConsumption memoryGas(ExpressionClasses::Id _position);
/// @returns the memory gas for accessing the memory at a specific offset for a number of bytes
/// given as values on the stack at the given relative positions.
GasConsumption memoryGas(int _stackPosOffset, int _stackPosSize);
std::shared_ptr<KnownState> m_state;
/// Largest point where memory was accessed since the creation of this object.
u256 m_largestMemoryAccess;
EVMSchedule m_schedule;
};
inline std::ostream& operator<<(std::ostream& _str, GasMeter::GasConsumption const& _consumption)
{
if (_consumption.isInfinite)
return _str << "[???]";
else
return _str << std::dec << _consumption.value;
}
}
}
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