From dec67df8d8e1446e6dfa94e2418889f18da5c3b9 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Thu, 3 Feb 2022 11:41:55 +0100
Subject: [PATCH] Refactor.

---
 libsolutil/LP.cpp             | 17 +++++++++--------
 libsolutil/LinearExpression.h |  6 +++++-
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/libsolutil/LP.cpp b/libsolutil/LP.cpp
index ef9da97b0..a1d6ae8a2 100644
--- a/libsolutil/LP.cpp
+++ b/libsolutil/LP.cpp
@@ -394,6 +394,8 @@ void removeColumns(SolvingState& _state, vector<bool> const& _columnsToRemove)
 	eraseIndices(_state.variableNames, _columnsToRemove);
 }
 
+// TODO move this into a simplifier class
+
 /// Turn constraints of the form ax <= b into an upper bound on x.
 /// @returns false if the system is infeasible.
 bool extractDirectConstraints(SolvingState& _state, bool& _changed)
@@ -416,8 +418,8 @@ bool extractDirectConstraints(SolvingState& _state, bool& _changed)
 		{
 			// 0 <= b or 0 = b
 			if (
-				constraint.data.factors.front() < 0 ||
-				(constraint.equality && constraint.data.factors.front() != 0)
+				constraint.data.front().numerator() < 0 ||
+				(constraint.equality && constraint.data.front())
 			)
 				return false; // Infeasible.
 		}
@@ -468,7 +470,7 @@ bool removeFixedVariables(SolvingState& _state, map<string, rational>& _model, b
 
 		// substitute variable
 		for (Constraint& constraint: _state.constraints)
-			if (constraint.data.factors.at(index) != 0)
+			if (constraint.data[index])
 			{
 				constraint.data[0] -= constraint.data[index] * lower;
 				constraint.data[index] = 0;
@@ -601,7 +603,7 @@ struct ProblemSplitter
 			Constraint splitRow{{}, state.constraints[i].equality};
 			for (size_t j = 0; j < state.constraints[i].data.size(); j++)
 				if (j == 0 || includedColumns[j])
-					splitRow.data.factors.push_back(state.constraints[i].data[j]);
+					splitRow.data.push_back(state.constraints[i].data[j]);
 			splitOff.constraints.push_back(move(splitRow));
 		}
 
@@ -730,7 +732,7 @@ string SolvingState::toString() const
 		result +=
 			joinHumanReadable(line, " + ") +
 			(constraint.equality ? "  = " : " <= ") +
-			::toString(constraint.data.factors.front()) +
+			::toString(constraint.data.front()) +
 			"\n";
 	}
 	result += "Bounds:\n";
@@ -779,9 +781,8 @@ pair<LPResult, map<string, rational>> LPSolver::check(SolvingState _state)
 			else
 			{
 				LinearExpression objectives;
-				objectives.factors =
-					vector<rational>(1, rational(bigint(0))) +
-					vector<rational>(split.constraints.front().data.size() - 1, rational(bigint(1)));
+				objectives.resize(1);
+				objectives.resize(split.constraints.front().data.size(), rational(bigint(1)));
 				tie(lpResult, solution) = simplex(split.constraints, move(objectives));
 			}
 			m_cache.emplace(move(orig), make_pair(lpResult, solution));
diff --git a/libsolutil/LinearExpression.h b/libsolutil/LinearExpression.h
index 57a245ee3..add117f1a 100644
--- a/libsolutil/LinearExpression.h
+++ b/libsolutil/LinearExpression.h
@@ -41,8 +41,9 @@ using rational = boost::rational<bigint>;
  * factors[0] + factors[1] * X1 + factors[2] * X2 + ...
  * The set and order of variables is implied.
  */
-struct LinearExpression
+class LinearExpression
 {
+public:
 	/// Creates the expression "_factor * X_index"
 	static LinearExpression factorForVariable(size_t _index, rational _factor)
 	{
@@ -74,6 +75,8 @@ struct LinearExpression
 	auto begin() const { return factors.begin(); }
 	auto end() const { return factors.end(); }
 
+	rational const& front() const { return factors.front(); }
+
 	void push_back(rational _value) { factors.push_back(move(_value)); }
 
 	size_t size() const { return factors.size(); }
@@ -169,6 +172,7 @@ struct LinearExpression
 		return _x;
 	}
 
+private:
 	std::vector<rational> factors;
 };