mirror of
https://github.com/ethereum/solidity
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97 lines
3.2 KiB
C++
97 lines
3.2 KiB
C++
/*
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This file is part of cpp-ethereum.
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cpp-ethereum is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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cpp-ethereum is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
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*/
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/** @file GasMeter.cpp
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* @author Christian <c@ethdev.com>
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* @date 2015
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*/
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#pragma once
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#include <ostream>
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#include <tuple>
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#include <libevmasm/ExpressionClasses.h>
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#include <libevmasm/AssemblyItem.h>
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namespace dev
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{
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namespace eth
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{
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class KnownState;
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/**
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* Class that helps computing the maximum gas consumption for instructions.
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* Has to be initialized with a certain known state that will be automatically updated for
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* each call to estimateMax. These calls have to supply strictly subsequent AssemblyItems.
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* A new gas meter has to be constructed (with a new state) for control flow changes.
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*/
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class GasMeter
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{
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public:
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struct GasConsumption
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{
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GasConsumption(u256 _value = 0, bool _infinite = false): value(_value), isInfinite(_infinite) {}
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static GasConsumption infinite() { return GasConsumption(0, true); }
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GasConsumption& operator+=(GasConsumption const& _other);
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bool operator<(GasConsumption const& _other) const { return this->tuple() < _other.tuple(); }
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std::tuple<bool const&, u256 const&> tuple() const { return std::tie(isInfinite, value); }
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u256 value;
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bool isInfinite;
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};
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/// Constructs a new gas meter given the current state.
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explicit GasMeter(std::shared_ptr<KnownState> const& _state, u256 const& _largestMemoryAccess = 0):
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m_state(_state), m_largestMemoryAccess(_largestMemoryAccess) {}
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/// @returns an upper bound on the gas consumed by the given instruction and updates
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/// the state.
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GasConsumption estimateMax(AssemblyItem const& _item);
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u256 const& largestMemoryAccess() const { return m_largestMemoryAccess; }
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static u256 runGas(Instruction _instruction);
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private:
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/// @returns _multiplier * (_value + 31) / 32, if _value is a known constant and infinite otherwise.
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GasConsumption wordGas(u256 const& _multiplier, ExpressionClasses::Id _value);
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/// @returns the gas needed to access the given memory position.
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/// @todo this assumes that memory was never accessed before and thus over-estimates gas usage.
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GasConsumption memoryGas(ExpressionClasses::Id _position);
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/// @returns the memory gas for accessing the memory at a specific offset for a number of bytes
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/// given as values on the stack at the given relative positions.
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GasConsumption memoryGas(int _stackPosOffset, int _stackPosSize);
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std::shared_ptr<KnownState> m_state;
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/// Largest point where memory was accessed since the creation of this object.
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u256 m_largestMemoryAccess;
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};
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inline std::ostream& operator<<(std::ostream& _str, GasMeter::GasConsumption const& _consumption)
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{
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if (_consumption.isInfinite)
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return _str << "[???]";
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else
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return _str << std::dec << _consumption.value;
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}
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}
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}
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