move libevmasm

1 files changed, 102 insertions, 0 deletions

diff --git a/libevmasm/GasMeter.h b/libevmasm/GasMeter.h
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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;
+}
+
+
+}
+}