Functional gas estimator.

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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/>.
+*/
+/**
+ * @author Christian <c@ethdev.com>
+ * @date 2015
+ * Gas consumption estimator working alongside the AST.
+ */
+
+#pragma once
+
+#include <vector>
+#include <map>
+#include <array>
+#include <libsolidity/ASTForward.h>
+#include <libevmasm/GasMeter.h>
+#include <libevmasm/Assembly.h>
+
+namespace dev
+{
+namespace solidity
+{
+
+struct GasEstimator
+{
+public:
+	using GasConsumption = eth::GasMeter::GasConsumption;
+	using ASTGasConsumption = std::map<ASTNode const*, GasConsumption>;
+	using ASTGasConsumptionSelfAccumulated =
+		std::map<ASTNode const*, std::array<GasConsumption, 2>>;
+
+	/// Estimates the gas consumption for every assembly item in the given assembly and stores
+	/// it by source location.
+	/// @returns a mapping from each AST node to a pair of its particular and syntactically accumulated gas costs.
+	static ASTGasConsumptionSelfAccumulated structuralEstimation(
+		eth::AssemblyItems const& _items,
+		std::vector<ASTNode const*> const& _ast
+	);
+	/// @returns a mapping from nodes with non-overlapping source locations to gas consumptions such that
+	/// the following source locations are part of the mapping:
+	/// 1. source locations of statements that do not contain other statements
+	/// 2. maximal source locations that do not overlap locations coming from the first rule
+	static ASTGasConsumption breakToStatementLevel(
+		ASTGasConsumptionSelfAccumulated const& _gasCosts,
+		std::vector<ASTNode const*> const& _roots
+	);
+
+	/// @returns the estimated gas consumption by the (public or external) function with the
+	/// given signature. If no signature is given, estimates the maximum gas usage.
+	static GasConsumption functionalEstimation(
+		eth::AssemblyItems const& _items,
+		std::string const& _signature = ""
+	);
+
+private:
+	/// @returns the set of AST nodes which are the finest nodes at their location.
+	static std::set<ASTNode const*> finestNodesAtLocation(std::vector<ASTNode const*> const& _roots);
+};
+
+}
+}