Structural gas estimator.

2 files changed, 171 insertions, 0 deletions

diff --git a/GasMeter.cpp b/GasMeter.cpp
new file mode 100644
index 00000000..e5fb0e09
--- /dev/null
+++ b/GasMeter.cpp
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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
+ */
+
+#include "GasMeter.h"
+#include <libevmcore/Params.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::eth;
+
+GasMeter::GasConsumption& GasMeter::GasConsumption::operator+=(GasConsumption const& _other)
+{
+	isInfinite = isInfinite || _other.isInfinite;
+	if (isInfinite)
+		return *this;
+	bigint v = bigint(value) + _other.value;
+	if (v > std::numeric_limits<u256>::max())
+		isInfinite = true;
+	else
+		value = u256(v);
+	return *this;
+}
+
+GasMeter::GasConsumption GasMeter::estimateMax(AssemblyItem const& _item)
+{
+	switch (_item.type()) {
+	case Push:
+	case PushTag:
+		return runGas(Instruction::PUSH1);
+	case Tag:
+		return runGas(Instruction::JUMPDEST);
+	case Operation:
+	{
+		GasConsumption gas = runGas(_item.instruction());
+		switch (_item.instruction())
+		{
+		case Instruction::SSTORE:
+			// @todo logic can be improved
+			gas += c_sstoreSetGas;
+			break;
+		case Instruction::SLOAD:
+			gas += c_sloadGas;
+			break;
+		case Instruction::MSTORE:
+		case Instruction::MSTORE8:
+		case Instruction::MLOAD:
+		case Instruction::RETURN:
+		case Instruction::SHA3:
+		case Instruction::CALLDATACOPY:
+		case Instruction::CODECOPY:
+		case Instruction::EXTCODECOPY:
+		case Instruction::LOG0:
+		case Instruction::LOG1:
+		case Instruction::LOG2:
+		case Instruction::LOG3:
+		case Instruction::LOG4:
+		case Instruction::CALL:
+		case Instruction::CALLCODE:
+		case Instruction::CREATE:
+		case Instruction::EXP:
+			// @todo logic can be improved
+			gas = GasConsumption::infinite();
+			break;
+		default:
+			break;
+		}
+		return gas;
+		break;
+	}
+	default:
+		break;
+	}
+
+	return GasConsumption::infinite();
+}
+
+GasMeter::GasConsumption GasMeter::runGas(Instruction _instruction)
+{
+	if (_instruction == Instruction::JUMPDEST)
+		return GasConsumption(1);
+
+	int tier = instructionInfo(_instruction).gasPriceTier;
+	return tier == InvalidTier ? GasConsumption::infinite() : c_tierStepGas[tier];
+}
+
+
diff --git a/GasMeter.h b/GasMeter.h
new file mode 100644
index 00000000..63dbc138
--- /dev/null
+++ b/GasMeter.h
@@ -0,0 +1,67 @@
+/*
+	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 <libevmasm/AssemblyItem.h>
+
+namespace dev
+{
+namespace eth
+{
+
+/**
+ * Class that helps computing the maximum gas consumption for instructions.
+ */
+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& _otherS);
+		std::ostream& operator<<(std::ostream& _str) const;
+
+		u256 value;
+		bool isInfinite;
+	};
+
+	/// Returns an upper bound on the gas consumed by the given instruction.
+	GasConsumption estimateMax(AssemblyItem const& _item);
+
+private:
+	static GasConsumption runGas(Instruction _instruction);
+};
+
+inline std::ostream& operator<<(std::ostream& _str, GasMeter::GasConsumption const& _consumption)
+{
+	if (_consumption.isInfinite)
+		return _str << "inf";
+	else
+		return _str << _consumption.value;
+}
+
+
+}
+}