simutrans depopulation

diff --git a/dataobj/einstellungen.cc b/dataobj/einstellungen.cc
index 3f0d236..9bc02a9 100644
--- a/dataobj/einstellungen.cc
+++ b/dataobj/einstellungen.cc
@@ -103,6 +103,8 @@ settings_t::settings_t() :
    mail_multiplier = 20;
    goods_multiplier = 20;
    electricity_multiplier = 0;
+   depopulation = 0;
+   increased_depop = 101;

    // Also there are size dependen factors (0 causes crash !)
    growthfactor_small = 400;
@@ -956,6 +958,9 @@ void settings_t::parse_simuconf(tabfile_t& simuconf, sint16& disp_width, sint16&
    goods_multiplier = contents.get_int("goods_multiplier", goods_multiplier );
    electricity_multiplier = contents.get_int("electricity_multiplier", electricity_multiplier );

+   depopulation = contents.get_int("depopulation", depopulation);
+   increased_depop = contents.get_int("increased_depop", increased_depop);
+
    growthfactor_small = contents.get_int("growthfactor_villages", growthfactor_small );
    growthfactor_medium = contents.get_int("growthfactor_cities", growthfactor_medium );
    growthfactor_large = contents.get_int("growthfactor_capitals", growthfactor_large );
diff --git a/dataobj/einstellungen.h b/dataobj/einstellungen.h
index c2c3ad2..bd76e2d 100644
--- a/dataobj/einstellungen.h
+++ b/dataobj/einstellungen.h
@@ -74,6 +74,9 @@ private:
    sint32 growthfactor_medium;
    sint32 growthfactor_large;

+   sint32 depopulation;
+   sint32 increased_depop;
+
    uint32 minimum_city_distance;
    uint32 industry_increase;

@@ -464,6 +467,8 @@ public:
    sint32 get_growthfactor_small() const { return growthfactor_small; }
    sint32 get_growthfactor_medium() const { return growthfactor_medium; }
    sint32 get_growthfactor_large() const { return growthfactor_large; }
+   sint32 get_depopulation() const { return depopulation; }
+   sint32 get_increased_depop() const {return increased_depop; }

    // percentage of passengers for different kinds of trips
    sint16 get_factory_worker_percentage() const { return factory_worker_percentage; }
diff --git a/simcity.cc b/simcity.cc
index 8399c4c..04be1c7 100644
--- a/simcity.cc
+++ b/simcity.cc
@@ -1053,6 +1053,8 @@ stadt_t::stadt_t(spieler_t* sp, koord pos, sint32 citizens) :
    check_bau_rathaus(true);

    wachstum = 0;
+   shrink = 0;
+   shrink_is_increased = false;
    allow_citygrowth = true;
    change_size( citizens );

@@ -1095,6 +1097,8 @@ stadt_t::stadt_t(karte_t* wl, loadsave_t* file) :
    has_low_density = false;

    wachstum = 0;
+   shrink = 0;
+   shrink_is_increased = false;
    name = NULL;
    stadtinfo_options = 3;

@@ -1438,6 +1442,7 @@ void stadt_t::step(long delta_t)
    }

    while(stadt_t::step_bau_interval < next_bau_step) {
+       step_depopulation();
        calc_growth();
        step_bau();
        next_bau_step -= stadt_t::step_bau_interval;
@@ -1461,7 +1466,42 @@ void stadt_t::step(long delta_t)
    city_history_year[0][HIST_BUILDING] = buildings.get_count();
 }

+/* performs depopulation */
+void stadt_t::step_depopulation()
+{
+   settings_t const&  s                    = welt->get_settings();
+   sint64     const(& h)[MAX_CITY_HISTORY] = city_history_month[1];
+   sint32     const   population           = get_einwohner();
+   sint32     const   not_transported      = (h[HIST_PAS_GENERATED] - h[HIST_PAS_TRANSPORTED]);
+   sint32     const   depopulation         = s.get_depopulation();
+   sint32     const   ratio_transported    = h[HIST_PAS_TRANSPORTED] / ((h[HIST_PAS_GENERATED] * s.get_increased_depop() / 100) + 1);
+   int        const   jobless              = (bev - arb);
+
+    // maybe this town should stay static
+   if(  !allow_citygrowth  ) {
+       shrink = 0;
+       return;
+   }

+   // after get_increased_depop() per cent of the generated passengers are transported the city depopulation will be faster
+   if ( !shrink_is_increased && (ratio_transported >= 1)) {
+       shrink_is_increased = true;
+   }
+
+   sint32 depop_factor = depopulation;
+   if ( shrink_is_increased ) depop_factor += depopulation;
+   // shrink is based on tatio of jobless and not transported passengers to city population
+   shrink += (jobless + not_transported) * depop_factor / (population+1);
+   const int shrink_step = (shrink>>4);
+   DBG_DEBUG("stadt_t::step_depopulation()", "depop_factor %i, depopulation %i; not_transported %i; jobless %i; shrink %i; shrink_step %i; shrink_is_increased %s; ratio_transported %i; increased_depop %i; population %i", depop_factor, depopulation, not_transported, jobless, shrink, shrink_step, (shrink_is_increased)?"true":"false", ratio_transported, s.get_increased_depop(), population);
+   shrink &= 0x0F;
+   // max. depopulation is normally lower value of jobless and calculated shrink
+   if ( (shrink_step <= jobless || shrink_is_increased) && bev > shrink_step ) bev -= shrink_step;
+   else if ( bev > jobless ) bev -= jobless;
+   // correct homeless, jobless < 0)
+   if (bev < won) won = bev;
+   if (bev < arb) arb = bev;
+}

 /* updates the city history
  * @author prissi
diff --git a/simcity.h b/simcity.h
index 5c9b1e5..47e18b4 100644
--- a/simcity.h
+++ b/simcity.h
@@ -154,6 +154,10 @@ private:
     */
    sint32 wachstum;

+   // used for city depopulation
+   sint32 shrink;
+   bool shrink_is_increased;
+
    /**
    * City history
    * @author prissi
@@ -259,6 +263,9 @@ private:
    // calculates the growth rate for next step_bau using all the different indicators
    void calc_growth();

+    /* performs depopulation */
+    void step_depopulation();
+
    /**
     * plant das bauen von Gebaeuden
     * @author Hj. Malthaner