(svn r25345) -Add: implementation of SharesMap and FlowStatMap

2 files changed, 264 insertions, 0 deletions

diff --git a/src/station_base.h b/src/station_base.h
index 974caa063..200d97a97 100644
--- a/src/station_base.h
+++ b/src/station_base.h
@@ -12,12 +12,14 @@
 #ifndef STATION_BASE_H
 #define STATION_BASE_H
 
+#include "core/random_func.hpp"
 #include "base_station_base.h"
 #include "newgrf_airport.h"
 #include "cargopacket.h"
 #include "industry_type.h"
 #include "linkgraph/linkgraph_type.h"
 #include "newgrf_storage.h"
+#include <map>
 
 typedef Pool<BaseStation, StationID, 32, 64000> StationPool;
 extern StationPool _station_pool;
@@ -25,6 +27,87 @@ extern StationPool _station_pool;
 static const byte INITIAL_STATION_RATING = 175;
 
 /**
+ * Flow statistics telling how much flow should be sent along a link. This is
+ * done by creating "flow shares" and using std::map's upper_bound() method to
+ * look them up with a random number. A flow share is the difference between a
+ * key in a map and the previous key. So one key in the map doesn't actually
+ * mean anything by itself.
+ */
+class FlowStat {
+public:
+	typedef std::map<uint32, StationID> SharesMap;
+
+	/**
+	 * Invalid constructor. This can't be called as a FlowStat must not be
+	 * empty. However, the constructor must be defined and reachable for
+	 * FlwoStat to be used in a std::map.
+	 */
+	inline FlowStat() {NOT_REACHED();}
+
+	/**
+	 * Create a FlowStat with an initial entry.
+	 * @param st Station the initial entry refers to.
+	 * @param flow Amount of flow for the initial entry.
+	 */
+	inline FlowStat(StationID st, uint flow)
+	{
+		assert(flow > 0);
+		this->shares[flow] = st;
+	}
+
+	/**
+	 * Add some flow to the end of the shares map. Only do that if you know
+	 * that the station isn't in the map yet. Anything else may lead to
+	 * inconsistencies.
+	 * @param st Remote station.
+	 * @param flow Amount of flow to be added.
+	 */
+	inline void AppendShare(StationID st, uint flow)
+	{
+		assert(flow > 0);
+		this->shares[(--this->shares.end())->first + flow] = st;
+	}
+
+	uint GetShare(StationID st) const;
+
+	void ChangeShare(StationID st, int flow);
+
+	/**
+	 * Get the actual shares as a const pointer so that they can be iterated
+	 * over.
+	 * @return Actual shares.
+	 */
+	inline const SharesMap *GetShares() const { return &this->shares; }
+
+	/**
+	 * Get a station a package can be routed to. This done by drawing a
+	 * random number between 0 and sum_shares and then looking that up in
+	 * the map with lower_bound. So each share gets selected with a
+	 * probability dependent on its flow.
+	 * @return A station ID from the shares map.
+	 */
+	inline StationID GetVia() const
+	{
+		assert(!this->shares.empty());
+		return this->shares.upper_bound(RandomRange((--this->shares.end())->first - 1))->second;
+	}
+
+	StationID GetVia(StationID excluded, StationID excluded2 = INVALID_STATION) const;
+
+private:
+	SharesMap shares;  ///< Shares of flow to be sent via specified station (or consumed locally).
+};
+
+/** Flow descriptions by origin stations. */
+class FlowStatMap : public std::map<StationID, FlowStat> {
+public:
+	void AddFlow(StationID origin, StationID via, uint amount);
+	void PassOnFlow(StationID origin, StationID via, uint amount);
+	void DeleteFlows(StationID via);
+	void FinalizeLocalConsumption(StationID self);
+};
+
+/**
  * Stores station stats for a single cargo.
  */
 struct GoodsEntry {
diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index 03003a518..1dad5d292 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -3979,6 +3979,187 @@ static CommandCost TerraformTile_Station(TileIndex tile, DoCommandFlag flags, in
 	return DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
 }
 
+/**
+ * Get flow for a station.
+ * @param st Station to get flow for.
+ * @return Flow for st.
+ */
+uint FlowStat::GetShare(StationID st) const
+{
+	uint32 prev = 0;
+	for (SharesMap::const_iterator it = this->shares.begin(); it != this->shares.end(); ++it) {
+		if (it->second == st) {
+			return it->first - prev;
+		} else {
+			prev = it->first;
+		}
+	}
+	return 0;
+}
+
+/**
+ * Get a station a package can be routed to, but exclude the given one.
+ * @param excluded StationID not to be selected.
+ * @return A station ID from the shares map.
+ */
+StationID FlowStat::GetVia(StationID excluded, StationID excluded2) const
+{
+	assert(!this->shares.empty());
+	uint max = (--this->shares.end())->first - 1;
+	SharesMap::const_iterator it = this->shares.upper_bound(RandomRange(max));
+	assert(it != this->shares.end());
+	if (it->second != excluded && it->second != excluded2) return it->second;
+
+	/* We've hit one of the excluded stations.
+	 * Draw another share, from outside its range. */
+
+	uint end = it->first;
+	uint begin = (it == this->shares.begin() ? 0 : (--it)->first);
+	uint interval = end - begin;
+	if (interval > max) return INVALID_STATION; // Only one station in the map.
+	uint new_max = max - interval;
+	uint rand = RandomRange(new_max);
+	SharesMap::const_iterator it2 = (rand < begin) ? this->shares.upper_bound(rand) :
+			this->shares.upper_bound(rand + interval);
+	assert(it2 != this->shares.end());
+	if (it2->second != excluded && it2->second != excluded2) return it2->second;
+
+	/* We've hit the second excluded station.
+	 * Same as before, only a bit more complicated. */
+
+	uint end2 = it2->first;
+	uint begin2 = (it2 == this->shares.begin() ? 0 : (--it2)->first);
+	uint interval2 = end2 - begin2;
+	if (interval2 > new_max) return INVALID_STATION; // Only the two excluded stations in the map.
+	new_max -= interval2;
+	if (begin > begin2) {
+		Swap(begin, begin2);
+		Swap(end, end2);
+		Swap(interval, interval2);
+	}
+	rand = RandomRange(new_max);
+	SharesMap::const_iterator it3 = this->shares.end();
+	if (rand < begin) {
+		it3 = this->shares.upper_bound(rand);
+	} else if (rand < begin2 - interval) {
+		it3 = this->shares.upper_bound(rand + interval);
+	} else {
+		it3 = this->shares.upper_bound(rand + interval + interval2);
+	}
+	assert(it3 != this->shares.end());
+	return it3->second;
+
+}
+
+/**
+ * Change share for specified station. By specifing INT_MIN as parameter you
+ * can erase a share.
+ * @param st Next Hop to be removed.
+ * @param flow Share to be added or removed.
+ */
+void FlowStat::ChangeShare(StationID st, int flow)
+{
+	/* We assert only before changing as afterwards the shares can actually
+	 * be empty. In that case the whole flow stat must be deleted then. */
+	assert(!this->shares.empty());
+
+	int32 added_shares = 0;
+	uint32 last_share = 0;
+	SharesMap new_shares;
+	for (SharesMap::iterator it(this->shares.begin()); it != this->shares.end(); ++it) {
+		if (it->second == st) {
+			uint share = it->first - last_share;
+			int change = flow - added_shares;
+			uint new_share = (change < 0 && (uint)(-change) > share) ? 0 : share + change;
+			added_shares -= share;
+			added_shares += new_share;
+			if (new_share > 0) {
+				new_shares[it->first + added_shares] = it->second;
+			}
+		} else {
+			new_shares[it->first + added_shares] = it->second;
+		}
+		last_share = it->first;
+	}
+	if (flow > added_shares) {
+		new_shares[last_share + flow - added_shares] = st;
+	}
+	this->shares.swap(new_shares);
+}
+
+/**
+ * Add some flow from "origin", going via "via".
+ * @param origin Origin of the flow.
+ * @param via Next hop.
+ * @param flow Amount of flow to be added.
+ */
+void FlowStatMap::AddFlow(StationID origin, StationID via, uint flow)
+{
+	FlowStatMap::iterator origin_it = this->find(origin);
+	if (origin_it == this->end()) {
+		this->insert(std::make_pair(origin, FlowStat(via, flow)));
+	} else {
+		origin_it->second.ChangeShare(via, flow);
+		assert(!origin_it->second.GetShares()->empty());
+	}
+}
+
+/**
+ * Pass on some flow, remembering it as invalid, for later subtraction from
+ * locally consumed flow. This is necessary because we can't have negative
+ * flows and we don't want to sort the flows before adding them up.
+ * @param origin Origin of the flow.
+ * @param via Next hop.
+ * @param flow Amount of flow to be passed.
+ */
+void FlowStatMap::PassOnFlow(StationID origin, StationID via, uint flow)
+{
+	FlowStatMap::iterator prev_it = this->find(origin);
+	if (prev_it == this->end()) {
+		FlowStat fs(via, flow);
+		fs.AppendShare(INVALID_STATION, flow);
+		this->insert(std::make_pair(origin, fs));
+	} else {
+		prev_it->second.ChangeShare(via, flow);
+		prev_it->second.ChangeShare(INVALID_STATION, flow);
+		assert(!prev_it->second.GetShares()->empty());
+	}
+}
+
+/**
+ * Subtract invalid flows from locally consumed flow.
+ * @param self ID of own station.
+ */
+void FlowStatMap::FinalizeLocalConsumption(StationID self)
+{
+	for (FlowStatMap::iterator i = this->begin(); i != this->end(); ++i) {
+		FlowStat &fs = i->second;
+		uint local = fs.GetShare(INVALID_STATION);
+		fs.ChangeShare(self, -local);
+		fs.ChangeShare(INVALID_STATION, -local);
+
+		/* If the local share is used up there must be a share for some
+		 * remote station. */
+		assert(!fs.GetShares()->empty());
+	}
+}
+
+/**
+ * Delete all flows at a station for specific cargo and destination.
+ * @param via Remote station of flows to be deleted.
+ */
+void FlowStatMap::DeleteFlows(StationID via)
+{
+	for (FlowStatMap::iterator f_it = this->begin(); f_it != this->end();) {
+		FlowStat &s_flows = f_it->second;
+		s_flows.ChangeShare(via, INT_MIN);
+		if (s_flows.GetShares()->empty()) {
+			this->erase(f_it++);
+		} else {
+			++f_it;
+		}
+	}
+}
 
 extern const TileTypeProcs _tile_type_station_procs = {
 	DrawTile_Station,           // draw_tile_proc