From b3b460cae294ccf31b013fbd8d198939afb6abef Mon Sep 17 00:00:00 2001
From: fonsinchen <fonsinchen@openttd.org>
Date: Sat, 19 Oct 2013 17:15:19 +0000
Subject: (svn r25885) -Codechange: Keep paths sorted so that the ones with
 flow == 0 are in the back and don't have to be iterated over so often.

---
 src/linkgraph/flowmapper.cpp   |  2 +-
 src/linkgraph/linkgraphjob.cpp |  2 +-
 src/linkgraph/linkgraphjob.h   |  5 +++--
 src/linkgraph/mcf.cpp          | 26 +++++++++++++++++++++++---
 4 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/src/linkgraph/flowmapper.cpp b/src/linkgraph/flowmapper.cpp
index 70779e8ec..b9aa9cd59 100644
--- a/src/linkgraph/flowmapper.cpp
+++ b/src/linkgraph/flowmapper.cpp
@@ -28,7 +28,7 @@ void FlowMapper::Run(LinkGraphJob &job) const
 		for (PathList::iterator i = paths.begin(); i != paths.end(); ++i) {
 			Path *path = *i;
 			uint flow = path->GetFlow();
-			if (flow == 0) continue;
+			if (flow == 0) break;
 			/* compress to monthly value */
 			flow = max(1U, flow * 30 / runtime);
 			Node node = job[path->GetNode()];
diff --git a/src/linkgraph/linkgraphjob.cpp b/src/linkgraph/linkgraphjob.cpp
index dcdc7ba36..242689e8d 100644
--- a/src/linkgraph/linkgraphjob.cpp
+++ b/src/linkgraph/linkgraphjob.cpp
@@ -181,7 +181,7 @@ uint Path::AddFlow(uint new_flow, LinkGraphJob &job, uint max_saturation)
 		}
 		new_flow = this->parent->AddFlow(new_flow, job, max_saturation);
 		if (this->flow == 0 && new_flow > 0) {
-			job[this->parent->node].Paths().push_back(this);
+			job[this->parent->node].Paths().push_front(this);
 		}
 		edge.AddFlow(new_flow);
 	}
diff --git a/src/linkgraph/linkgraphjob.h b/src/linkgraph/linkgraphjob.h
index 79231c754..66aff3672 100644
--- a/src/linkgraph/linkgraphjob.h
+++ b/src/linkgraph/linkgraphjob.h
@@ -45,7 +45,7 @@ private:
 	 */
 	struct NodeAnnotation {
 		uint undelivered_supply; ///< Amount of supply that hasn't been distributed yet.
-		PathList paths;          ///< Paths through this node.
+		PathList paths;          ///< Paths through this node, sorted so that those with flow == 0 are in the back.
 		FlowStatMap flows;       ///< Planned flows to other nodes.
 		void Init(uint supply);
 	};
@@ -234,7 +234,8 @@ public:
 		const FlowStatMap &Flows() const { return this->node_anno.flows; }
 
 		/**
-		 * Get the paths this node is part of.
+		 * Get the paths this node is part of. Paths are always expected to be
+		 * sorted so that those with flow == 0 are in the back of the list.
 		 * @return Paths.
 		 */
 		PathList &Paths() { return this->node_anno.paths; }
diff --git a/src/linkgraph/mcf.cpp b/src/linkgraph/mcf.cpp
index d07f147b2..af9f6ce5f 100644
--- a/src/linkgraph/mcf.cpp
+++ b/src/linkgraph/mcf.cpp
@@ -351,7 +351,17 @@ void MCF1stPass::EliminateCycle(PathVector &path, Path *cycle_begin, uint flow)
 	do {
 		NodeID prev = cycle_begin->GetNode();
 		cycle_begin->ReduceFlow(flow);
-		cycle_begin = path[cycle_begin->GetNode()];
+		if (cycle_begin->GetFlow() == 0) {
+			PathList &node_paths = this->job[cycle_begin->GetParent()->GetNode()].Paths();
+			for (PathList::iterator i = node_paths.begin(); i != node_paths.end(); ++i) {
+				if (*i == cycle_begin) {
+					node_paths.erase(i);
+					node_paths.push_back(cycle_begin);
+					break;
+				}
+			}
+		}
+		cycle_begin = path[prev];
 		Edge edge = this->job[prev][cycle_begin->GetNode()];
 		edge.RemoveFlow(flow);
 	} while (cycle_begin != cycle_end);
@@ -379,18 +389,28 @@ bool MCF1stPass::EliminateCycles(PathVector &path, NodeID origin_id, NodeID next
 		 * in one path each. */
 		PathList &paths = this->job[next_id].Paths();
 		PathViaMap next_hops;
-		for (PathList::iterator i = paths.begin(); i != paths.end(); ++i) {
+		for (PathList::iterator i = paths.begin(); i != paths.end();) {
 			Path *new_child = *i;
+			uint new_flow = new_child->GetFlow();
+			if (new_flow == 0) break;
 			if (new_child->GetOrigin() == origin_id) {
 				PathViaMap::iterator via_it = next_hops.find(new_child->GetNode());
 				if (via_it == next_hops.end()) {
 					next_hops[new_child->GetNode()] = new_child;
+					++i;
 				} else {
 					Path *child = via_it->second;
-					uint new_flow = new_child->GetFlow();
 					child->AddFlow(new_flow);
 					new_child->ReduceFlow(new_flow);
+
+					/* We might hit end() with with the ++ here and skip the
+					 * newly push_back'ed path. That's good as the flow of that
+					 * path is 0 anyway. */
+					paths.erase(i++);
+					paths.push_back(new_child);
 				}
+			} else {
+				++i;
 			}
 		}
 		bool found = false;
-- 
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