(svn r5999) -Feature: change the original date format to a 32 bits format based at the year 0.

The game date subsystem now allows someone to start in the year 0 and continue
up to the year 5 000 000. However, you currently cannot build anything before 
1920 as there is no newgrf support for dates before 1920 or after 2090 yet.

25 files changed, 165 insertions, 92 deletions

diff --git a/date.c b/date.c
index def44e6f8..2bb1596b1 100644
--- a/date.c
+++ b/date.c
@@ -70,25 +70,47 @@ static const uint16 _accum_days_for_month[] = {
 	ACCUM_SEP, ACCUM_OCT, ACCUM_NOV, ACCUM_DEC,
 };
 
+static inline bool IsLeapYear(Year yr)
+{
+	return yr % 4 == 0 && (yr % 100 != 0 || yr % 400 == 0);
+}
 
+/**
+ * Converts a Date to a Year, Month & Day.
+ * @param date the date to convert from
+ * @param ymd  the year, month and day to write to
+ */
 void ConvertDateToYMD(Date date, YearMonthDay *ymd)
 {
-	uint yr  = date / (365 + 365 + 365 + 366);
-	uint rem = date % (365 + 365 + 365 + 366);
-	uint x;
-
-	yr *= 4;
-
-	if (rem >= 366) {
-		rem--;
-		do {
-			rem -= 365;
-			yr++;
-		} while (rem >= 365);
-		if (rem >= 31 + 28) rem++;
+	/*
+	 * Year determination in multiple steps to account for leap
+	 * years. First do the large steps, then the smaller ones.
+	 */
+
+	/* There are 97 leap years in 400 years */
+	Year yr = 400 * (date / (365 * 400 + 97));
+	int rem = date % (365 * 400 + 97);
+	uint16 x;
+
+	/* There are 24 leap years in 100 years */
+	yr += 100 * (rem / (365 * 100 + 24));
+	rem = rem % (365 * 100 + 24);
+
+	/* There is 1 leap year every 4 years */
+	yr += 4 * (rem / (365 * 4 + 1));
+	rem = rem % (365 * 4 + 1);
+
+	/* The last (max 3) years to account for; the first one
+	 * can be, but is not necessarily a leap year */
+	while (rem >= (IsLeapYear(yr) ? 366 : 365)) {
+		rem -= IsLeapYear(yr) ? 366 : 365;
+		yr++;
 	}
 
-	ymd->year = BASE_YEAR + yr;
+	/* Skip the 29th of February in non-leap years */
+	if (!IsLeapYear(yr) && rem >= ACCUM_MAR - 1) rem++;
+
+	ymd->year = yr;
 
 	x = _month_date_from_year_day[rem];
 	ymd->month = x >> 5;
@@ -97,23 +119,28 @@ void ConvertDateToYMD(Date date, YearMonthDay *ymd)
 
 /**
  * Converts a tupe of Year, Month and Day to a Date.
- * @param year  is a number between 0..?
+ * @param year  is a number between 0..MAX_YEAR
  * @param month is a number between 0..11
  * @param day   is a number between 1..31
  */
 Date ConvertYMDToDate(Year year, Month month, Day day)
 {
-	uint rem;
-	uint yr = year - BASE_YEAR;
-
-	/* day in the year */
-	rem = _accum_days_for_month[month] + day - 1;
-
-	/* remove feb 29 from year 1,2,3 */
-	if (yr & 3) rem += (yr & 3) * 365 + (rem < 31 + 29);
-
-	/* base date. */
-	return (yr >> 2) * (365 + 365 + 365 + 366) + rem;
+	/*
+	 * Each passed leap year adds one day to the 'day count'.
+	 *
+	 * A special case for the year 0 as no year has been passed,
+	 * but '(year - 1) / 4' does not yield '-1' to counteract the
+	 * '+1' at the end of the formula as divisions round to zero.
+	 */
+	int nr_of_leap_years = (year == 0) ? 0 : ((year - 1) / 4 - (year - 1) / 100 + (year - 1) / 400 + 1);
+
+	/* Day-offset in a leap year */
+	int days = _accum_days_for_month[month] + day - 1;
+
+	/* Account for the missing of the 29th of February in non-leap years */
+	if (!IsLeapYear(year) && days >= ACCUM_MAR) days--;
+
+	return year * 365 + nr_of_leap_years + days;
 }
 
 /** Functions used by the IncreaseDate function */
@@ -252,12 +279,12 @@ void IncreaseDate(void)
 	/* check if we reached the maximum year, decrement dates by a year */
 	} else if (_cur_year == MAX_YEAR + 1) {
 		Vehicle *v;
+		uint days_this_year;
 
 		_cur_year--;
-		_date -= 365;
-		FOR_ALL_VEHICLES(v) {
-			v->date_of_last_service -= 365;
-		}
+		days_this_year = IsLeapYear(_cur_year) ? 366 : 365;
+		_date -= days_this_year;
+		FOR_ALL_VEHICLES(v) v->date_of_last_service -= days_this_year;
 
 		/* Because the _date wraps here, and text-messages expire by game-days, we have to clean out
 		 *  all of them if the date is set back, else those messages will hang for ever */
diff --git a/date.h b/date.h
index 1b5288599..58f952a19 100644
--- a/date.h
+++ b/date.h
@@ -24,14 +24,16 @@
  * The offset in days from the '_date == 0' till
  * 'ConvertYMDToDate(ORIGINAL_BASE_YEAR, 0, 1)'
  */
-#define DAYS_TILL_ORIGINAL_BASE_YEAR 0
+#define DAYS_TILL_ORIGINAL_BASE_YEAR (365 * ORIGINAL_BASE_YEAR + ORIGINAL_BASE_YEAR / 4 - ORIGINAL_BASE_YEAR / 100 + ORIGINAL_BASE_YEAR / 400)
 
 /* Temporary value to make transition to full past 2090 easier/more clear */
-#define BASE_YEAR 1920
+#define BASE_YEAR 0
 
 /* The absolute minimum & maximum years in OTTD */
-#define MIN_YEAR 1920
-#define MAX_YEAR 2090
+#define MIN_YEAR 0
+/* MAX_YEAR, nicely rounded value of the number of years that can
+ * be encoded in a single 32 bits date, about 2^31 / 366 years. */
+#define MAX_YEAR 5000000
 
 /* Year and Date are defined elsewhere */
 typedef uint8  Month;
diff --git a/engine.c b/engine.c
index ceaa91fb4..2069d14a8 100644
--- a/engine.c
+++ b/engine.c
@@ -606,8 +606,10 @@ static void Load_ERNW(void)
 }
 
 static const SaveLoad _engine_desc[] = {
-	SLE_VAR(Engine,intro_date,						SLE_UINT16),
-	SLE_VAR(Engine,age,										SLE_UINT16),
+	SLE_CONDVAR(Engine,intro_date,				SLE_FILE_U16 | SLE_VAR_I32,  0,  30),
+	SLE_CONDVAR(Engine,intro_date,				SLE_INT32, 31, SL_MAX_VERSION),
+	SLE_CONDVAR(Engine,age,								SLE_FILE_U16 | SLE_VAR_I32,  0,  30),
+	SLE_CONDVAR(Engine,age,								SLE_INT32, 31, SL_MAX_VERSION),
 	SLE_VAR(Engine,reliability,						SLE_UINT16),
 	SLE_VAR(Engine,reliability_spd_dec,		SLE_UINT16),
 	SLE_VAR(Engine,reliability_start,			SLE_UINT16),
diff --git a/engine.h b/engine.h
index c62c1900a..6df7c650a 100644
--- a/engine.h
+++ b/engine.h
@@ -76,8 +76,8 @@ typedef struct RoadVehicleInfo {
 typedef struct EngineInfo {
 	Date base_intro;
 	byte unk2;              ///< Carriages have the highest bit set in this one
-	byte lifelength;
-	byte base_life;
+	Year lifelength;
+	Year base_life;
 	byte railtype:4;
 	byte climates:4;
 	uint32 refit_mask;
diff --git a/genworld_gui.c b/genworld_gui.c
index a00046658..9ca71a463 100644
--- a/genworld_gui.c
+++ b/genworld_gui.c
@@ -362,7 +362,7 @@ void GenerateLandscapeWndProc(Window *w, WindowEvent *e)
 		case 19: // Year text
 			WP(w, def_d).data_3 = START_DATE_QUERY;
 			SetDParam(0, _patches_newgame.starting_year);
-			ShowQueryString(STR_CONFIG_PATCHES_INT32, STR_START_DATE_QUERY_CAPT, 5, 100, WC_GENERATE_LANDSCAPE, mode, CS_NUMERAL);
+			ShowQueryString(STR_CONFIG_PATCHES_INT32, STR_START_DATE_QUERY_CAPT, 8, 100, WC_GENERATE_LANDSCAPE, mode, CS_NUMERAL);
 			break;
 		case 21: case 23: // Snow line buttons
 			/* Don't allow too fast scrolling */
@@ -629,7 +629,7 @@ void CreateScenarioWndProc(Window *w, WindowEvent *e)
 		case 15: // Year text
 			WP(w, def_d).data_3 = START_DATE_QUERY;
 			SetDParam(0, _patches_newgame.starting_year);
-			ShowQueryString(STR_CONFIG_PATCHES_INT32, STR_START_DATE_QUERY_CAPT, 5, 100, WC_GENERATE_LANDSCAPE, GLWP_SCENARIO, CS_NUMERAL);
+			ShowQueryString(STR_CONFIG_PATCHES_INT32, STR_START_DATE_QUERY_CAPT, 8, 100, WC_GENERATE_LANDSCAPE, GLWP_SCENARIO, CS_NUMERAL);
 			break;
 		case 17: case 19: // Height level buttons
 			/* Don't allow too fast scrolling */
diff --git a/industry.h b/industry.h
index 0189a6d84..a4b8dd50e 100644
--- a/industry.h
+++ b/industry.h
@@ -28,7 +28,7 @@ struct Industry {
 	byte type;
 	byte owner;
 	byte color_map;
-	byte last_prod_year;
+	Year last_prod_year;
 	byte was_cargo_delivered;
 
 	uint16 index;
diff --git a/industry_cmd.c b/industry_cmd.c
index cf6592155..a22225efb 100644
--- a/industry_cmd.c
+++ b/industry_cmd.c
@@ -1929,7 +1929,8 @@ static const SaveLoad _industry_desc[] = {
 	SLE_VAR(Industry,type,						SLE_UINT8),
 	SLE_VAR(Industry,owner,						SLE_UINT8),
 	SLE_VAR(Industry,color_map,				SLE_UINT8),
-	SLE_VAR(Industry,last_prod_year,	SLE_UINT8),
+	SLE_CONDVAR(Industry, last_prod_year,	SLE_FILE_U8 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Industry, last_prod_year,	SLE_INT32, 31, SL_MAX_VERSION),
 	SLE_VAR(Industry,was_cargo_delivered,SLE_UINT8),
 
 	// reserve extra space in savegame here. (currently 32 bytes)
diff --git a/misc.c b/misc.c
index e18db9bb1..0f2aad00a 100644
--- a/misc.c
+++ b/misc.c
@@ -268,7 +268,8 @@ static void Load_NAME(void)
 }
 
 static const SaveLoadGlobVarList _date_desc[] = {
-	    SLEG_VAR(_date,                  SLE_UINT16),
+	SLEG_CONDVAR(_date,                  SLE_FILE_U16 | SLE_VAR_U32,  0,  30),
+	SLEG_CONDVAR(_date,                  SLE_UINT32, 31, SL_MAX_VERSION),
 	    SLEG_VAR(_date_fract,            SLE_UINT16),
 	    SLEG_VAR(_tick_counter,          SLE_UINT16),
 	    SLEG_VAR(_vehicle_id_ctr_day,    SLE_UINT16),
diff --git a/misc_gui.c b/misc_gui.c
index 043b64070..5754e422a 100644
--- a/misc_gui.c
+++ b/misc_gui.c
@@ -1714,7 +1714,7 @@ static const CheatEntry _cheats_ui[] = {
 	{SLE_BOOL,       0, STR_CHEAT_NO_JETCRASH,    &_cheats.no_jetcrash.value,     &_cheats.no_jetcrash.been_used,     NULL,                     0,  0},
 	{SLE_BOOL,       0, STR_CHEAT_SETUP_PROD,     &_cheats.setup_prod.value,      &_cheats.setup_prod.been_used,      NULL,                     0,  0},
 	{SLE_UINT8,      0, STR_CHEAT_SWITCH_CLIMATE, &_opt.landscape,                &_cheats.switch_climate.been_used,  &ClickChangeClimateCheat,-1,  4},
-	{SLE_UINT8,      0, STR_CHEAT_CHANGE_DATE,    &_cur_year,                     &_cheats.change_date.been_used,     &ClickChangeDateCheat,   -1,  1},
+	{SLE_INT32,      0, STR_CHEAT_CHANGE_DATE,    &_cur_year,                     &_cheats.change_date.been_used,     &ClickChangeDateCheat,   -1,  1},
 	{SLE_BOOL,       0, STR_CHEAT_ALLOW_CONVRAIL, &_cheats.elrail.value,          &_cheats.elrail.been_used,          &ClickAllowConvrail,      0,  0},
 };
 
diff --git a/network.h b/network.h
index 6225c8e9e..628b78203 100644
--- a/network.h
+++ b/network.h
@@ -89,7 +89,7 @@ typedef struct NetworkGameInfo {
 typedef struct NetworkPlayerInfo {
 	char company_name[NETWORK_NAME_LENGTH];					// Company name
 	char password[NETWORK_PASSWORD_LENGTH];					// The password for the player
-	byte inaugurated_year;													// What year the company started in
+	Year inaugurated_year;													// What year the company started in
 	int64 company_value;														// The company value
 	int64 money;																		// The amount of money the company has
 	int64 income;																		// How much did the company earned last year
diff --git a/network_client.c b/network_client.c
index 4a02ee2a3..0943d5f75 100644
--- a/network_client.c
+++ b/network_client.c
@@ -300,7 +300,7 @@ DEF_CLIENT_RECEIVE_COMMAND(PACKET_SERVER_COMPANY_INFO)
 			return NETWORK_RECV_STATUS_CLOSE_QUERY;
 
 		NetworkRecv_string(MY_CLIENT, p, _network_player_info[current].company_name, sizeof(_network_player_info[current].company_name));
-		_network_player_info[current].inaugurated_year = NetworkRecv_uint8(MY_CLIENT, p);
+		_network_player_info[current].inaugurated_year = NetworkRecv_uint32(MY_CLIENT, p);
 		_network_player_info[current].company_value = NetworkRecv_uint64(MY_CLIENT, p);
 		_network_player_info[current].money = NetworkRecv_uint64(MY_CLIENT, p);
 		_network_player_info[current].income = NetworkRecv_uint64(MY_CLIENT, p);
diff --git a/network_data.h b/network_data.h
index e24a1deea..5415b6337 100644
--- a/network_data.h
+++ b/network_data.h
@@ -18,9 +18,9 @@
 #define NETWORK_EMPTY_INDEX 0
 
 // What version of game-info do we use?
-#define NETWORK_GAME_INFO_VERSION 2
+#define NETWORK_GAME_INFO_VERSION 3
 // What version of company info is this?
-#define NETWORK_COMPANY_INFO_VERSION 3
+#define NETWORK_COMPANY_INFO_VERSION 4
 // What version of master-server-protocol do we use?
 #define NETWORK_MASTER_SERVER_VERSION 1
 
diff --git a/network_server.c b/network_server.c
index b4e05f940..3c18e75ff 100644
--- a/network_server.c
+++ b/network_server.c
@@ -95,7 +95,7 @@ DEF_SERVER_SEND_COMMAND(PACKET_SERVER_COMPANY_INFO)
 		NetworkSend_uint8 (p, player->index);
 
 		NetworkSend_string(p, _network_player_info[player->index].company_name);
-		NetworkSend_uint8 (p, _network_player_info[player->index].inaugurated_year);
+		NetworkSend_uint32(p, _network_player_info[player->index].inaugurated_year);
 		NetworkSend_uint64(p, _network_player_info[player->index].company_value);
 		NetworkSend_uint64(p, _network_player_info[player->index].money);
 		NetworkSend_uint64(p, _network_player_info[player->index].income);
diff --git a/network_udp.c b/network_udp.c
index de811c722..aacf53372 100644
--- a/network_udp.c
+++ b/network_udp.c
@@ -63,6 +63,10 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_FIND_SERVER)
 
 	NetworkSend_uint8 (packet, NETWORK_GAME_INFO_VERSION);
 
+	/* NETWORK_GAME_INFO_VERSION = 3 */
+	NetworkSend_uint32(packet, _network_game_info.game_date);
+	NetworkSend_uint32(packet, _network_game_info.start_date);
+
 	/* NETWORK_GAME_INFO_VERSION = 2 */
 	NetworkSend_uint8 (packet, _network_game_info.companies_max);
 	NetworkSend_uint8 (packet, ActivePlayerCount());
@@ -76,8 +80,6 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_FIND_SERVER)
 	NetworkSend_uint8 (packet, _network_game_info.clients_max);
 	NetworkSend_uint8 (packet, _network_game_info.clients_on);
 	NetworkSend_uint8 (packet, NetworkSpectatorCount());
-	NetworkSend_uint16(packet, _network_game_info.game_date);
-	NetworkSend_uint16(packet, _network_game_info.start_date);
 	NetworkSend_string(packet, _network_game_info.map_name);
 	NetworkSend_uint16(packet, _network_game_info.map_width);
 	NetworkSend_uint16(packet, _network_game_info.map_height);
@@ -114,6 +116,10 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_SERVER_RESPONSE)
 	/* Please observer the order. In the order in which packets are sent
 	 * they are to be received */
 	switch (game_info_version) {
+		case 3:
+			item->info.game_date     = NetworkRecv_uint32(&_udp_cs, p);
+			item->info.start_date    = NetworkRecv_uint32(&_udp_cs, p);
+			/* Fallthrough */
 		case 2:
 			item->info.companies_max = NetworkRecv_uint8(&_udp_cs, p);
 			item->info.companies_on = NetworkRecv_uint8(&_udp_cs, p);
@@ -127,8 +133,10 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_SERVER_RESPONSE)
 			item->info.clients_max   = NetworkRecv_uint8(&_udp_cs, p);
 			item->info.clients_on    = NetworkRecv_uint8(&_udp_cs, p);
 			item->info.spectators_on = NetworkRecv_uint8(&_udp_cs, p);
-			item->info.game_date     = NetworkRecv_uint16(&_udp_cs, p);
-			item->info.start_date    = NetworkRecv_uint16(&_udp_cs, p);
+			if (game_info_version < 3) { // 16 bits dates got scrapped and are read earlier
+				item->info.game_date     = NetworkRecv_uint16(&_udp_cs, p) + DAYS_TILL_ORIGINAL_BASE_YEAR;
+				item->info.start_date    = NetworkRecv_uint16(&_udp_cs, p) + DAYS_TILL_ORIGINAL_BASE_YEAR;
+			}
 			NetworkRecv_string(&_udp_cs, p, item->info.map_name, sizeof(item->info.map_name));
 			item->info.map_width     = NetworkRecv_uint16(&_udp_cs, p);
 			item->info.map_height    = NetworkRecv_uint16(&_udp_cs, p);
@@ -185,7 +193,7 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_DETAIL_INFO)
 		NetworkSend_uint8(packet, current);
 
 		NetworkSend_string(packet, _network_player_info[player->index].company_name);
-		NetworkSend_uint8 (packet, _network_player_info[player->index].inaugurated_year);
+		NetworkSend_uint32(packet, _network_player_info[player->index].inaugurated_year);
 		NetworkSend_uint64(packet, _network_player_info[player->index].company_value);
 		NetworkSend_uint64(packet, _network_player_info[player->index].money);
 		NetworkSend_uint64(packet, _network_player_info[player->index].income);
@@ -212,7 +220,7 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_DETAIL_INFO)
 				NetworkSend_uint8(packet, 1);
 				NetworkSend_string(packet, ci->client_name);
 				NetworkSend_string(packet, ci->unique_id);
-				NetworkSend_uint16(packet, ci->join_date);
+				NetworkSend_uint32(packet, ci->join_date);
 			}
 		}
 		/* Also check for the server itself */
@@ -222,7 +230,7 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_DETAIL_INFO)
 			NetworkSend_uint8(packet, 1);
 			NetworkSend_string(packet, ci->client_name);
 			NetworkSend_string(packet, ci->unique_id);
-			NetworkSend_uint16(packet, ci->join_date);
+			NetworkSend_uint32(packet, ci->join_date);
 		}
 
 		/* Indicates end of client list */
@@ -237,7 +245,7 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_DETAIL_INFO)
 			NetworkSend_uint8(packet, 1);
 			NetworkSend_string(packet, ci->client_name);
 			NetworkSend_string(packet, ci->unique_id);
-			NetworkSend_uint16(packet, ci->join_date);
+			NetworkSend_uint32(packet, ci->join_date);
 		}
 	}
 	/* Also check for the server itself */
@@ -247,7 +255,7 @@ DEF_UDP_RECEIVE_COMMAND(PACKET_UDP_CLIENT_DETAIL_INFO)
 		NetworkSend_uint8(packet, 1);
 		NetworkSend_string(packet, ci->client_name);
 		NetworkSend_string(packet, ci->unique_id);
-		NetworkSend_uint16(packet, ci->join_date);
+		NetworkSend_uint32(packet, ci->join_date);
 	}
 
 	/* Indicates end of client list */
diff --git a/oldloader.c b/oldloader.c
index ce3a78d1d..9bb33eb1f 100644
--- a/oldloader.c
+++ b/oldloader.c
@@ -702,7 +702,7 @@ static const OldChunks industry_chunk[] = {
 	OCL_SVAR(  OC_UINT8, Industry, type ),
 	OCL_SVAR(  OC_UINT8, Industry, owner ),
 	OCL_SVAR(  OC_UINT8, Industry, color_map ),
-	OCL_SVAR(  OC_UINT8, Industry, last_prod_year ),
+	OCL_SVAR( OC_FILE_U8 | OC_VAR_I32, Industry, last_prod_year ),
 	OCL_SVAR( OC_UINT16, Industry, counter ),
 	OCL_SVAR(  OC_UINT8, Industry, was_cargo_delivered ),
 
@@ -995,7 +995,7 @@ static bool LoadOldPlayer(LoadgameState *ls, int num)
 		p->money64 = p->player_money = p->current_loan = 100000;
 
 	_player_colors[num] = p->player_color;
-	p->inaugurated_year = _old_inaugurated_year - BASE_YEAR;
+	p->inaugurated_year = _old_inaugurated_year;
 	if (p->location_of_house == 0xFFFF)
 		p->location_of_house = 0;
 
@@ -1122,7 +1122,7 @@ static const OldChunks vehicle_chunk[] = {
 	OCL_SVAR(  OC_UINT8, Vehicle, cur_order_index ),
 	OCL_SVAR(   OC_TILE, Vehicle, dest_tile ),
 	OCL_SVAR( OC_UINT16, Vehicle, load_unload_time_rem ),
-	OCL_SVAR( OC_UINT16, Vehicle, date_of_last_service ),
+	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Vehicle, date_of_last_service ),
 	OCL_SVAR( OC_UINT16, Vehicle, service_interval ),
 	OCL_SVAR( OC_FILE_U8 | OC_VAR_U16, Vehicle, last_station_visited ),
 	OCL_SVAR(  OC_UINT8, Vehicle, tick_counter ),
@@ -1156,9 +1156,9 @@ static const OldChunks vehicle_chunk[] = {
 	OCL_SVAR( OC_FILE_U8 | OC_VAR_U16, Vehicle, cargo_source ),
 	OCL_SVAR(  OC_UINT8, Vehicle, cargo_days ),
 
-	OCL_SVAR( OC_UINT16, Vehicle, age ),
-	OCL_SVAR( OC_UINT16, Vehicle, max_age ),
-	OCL_SVAR(  OC_UINT8, Vehicle, build_year ),
+	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Vehicle, age ),
+	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Vehicle, max_age ),
+	OCL_SVAR( OC_FILE_U8 | OC_VAR_I32, Vehicle, build_year ),
 	OCL_SVAR( OC_FILE_U8 | OC_VAR_U16, Vehicle, unitnumber ),
 
 	OCL_SVAR( OC_UINT16, Vehicle, engine_type ),
@@ -1259,8 +1259,8 @@ static bool LoadOldSign(LoadgameState *ls, int num)
 
 static const OldChunks engine_chunk[] = {
 	OCL_SVAR( OC_UINT16, Engine, player_avail ),
-	OCL_SVAR( OC_UINT16, Engine, intro_date ),
-	OCL_SVAR( OC_UINT16, Engine, age ),
+	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Engine, intro_date ),
+	OCL_SVAR( OC_FILE_U16 | OC_VAR_U32, Engine, age ),
 	OCL_SVAR( OC_UINT16, Engine, reliability ),
 	OCL_SVAR( OC_UINT16, Engine, reliability_spd_dec ),
 	OCL_SVAR( OC_UINT16, Engine, reliability_start ),
@@ -1375,7 +1375,7 @@ static bool LoadOldMapPart2(LoadgameState *ls, int num)
 static uint32 _old_cur_town_ctr;
 static const OldChunks main_chunk[] = {
 	OCL_ASSERT( 0 ),
-	OCL_VAR ( OC_UINT16,   1, &_date ),
+	OCL_VAR ( OC_FILE_U16 | OC_VAR_U32, 1, &_date ),
 	OCL_VAR ( OC_UINT16,   1, &_date_fract ),
 	OCL_NULL( 600 ),            // TextEffects
 	OCL_VAR ( OC_UINT32,   2, &_random_seeds[0] ),
diff --git a/openttd.c b/openttd.c
index 708bfc317..4a71a589d 100644
--- a/openttd.c
+++ b/openttd.c
@@ -793,7 +793,7 @@ void SwitchMode(int new_mode)
 				}
 			}
 			_generating_world = false;
-			_patches_newgame.starting_year = BASE_YEAR + _cur_year;
+			_patches_newgame.starting_year = ORIGINAL_BASE_YEAR + _cur_year;
 			// delete all stations owned by a player
 			DeleteAllPlayerStations();
 		} else {
@@ -1439,5 +1439,29 @@ bool AfterLoadGame(void)
 
 	if (!CheckSavegameVersion(27)) AfterLoadStations();
 
+	/* Time starts at 0 instead of 1920.
+	 * Account for this in older games by adding an offset */
+	if (CheckSavegameVersion(31)) {
+		Station *st;
+		Waypoint *wp;
+		Engine *e;
+		Player *player;
+		Industry *i;
+		Vehicle *v;
+
+		_date += DAYS_TILL_ORIGINAL_BASE_YEAR;
+
+		FOR_ALL_STATIONS(st)    st->build_date += DAYS_TILL_ORIGINAL_BASE_YEAR;
+		FOR_ALL_WAYPOINTS(wp)   wp->build_date += DAYS_TILL_ORIGINAL_BASE_YEAR;
+		FOR_ALL_ENGINES(e)      e->intro_date  += DAYS_TILL_ORIGINAL_BASE_YEAR;
+		FOR_ALL_PLAYERS(player) player->inaugurated_year += ORIGINAL_BASE_YEAR;
+		FOR_ALL_INDUSTRIES(i)   i->last_prod_year        += ORIGINAL_BASE_YEAR;
+
+		FOR_ALL_VEHICLES(v) {
+			v->date_of_last_service += DAYS_TILL_ORIGINAL_BASE_YEAR;
+			v->build_year += ORIGINAL_BASE_YEAR;
+		}
+	}
+
 	return true;
 }
diff --git a/openttd.h b/openttd.h
index a7b2abd91..857f92b15 100644
--- a/openttd.h
+++ b/openttd.h
@@ -54,11 +54,11 @@ typedef byte WindowClass;
 
 enum {
 	INVALID_YEAR = -1,
-	INVALID_DATE = (uint16)-1,
+	INVALID_DATE = -1,
 };
 
-typedef int16  Year;
-typedef uint16 Date;
+typedef int32 Year;
+typedef int32 Date;
 
 
 enum GameModes {
diff --git a/player.h b/player.h
index 8dcbbd6b8..52f4bb18f 100644
--- a/player.h
+++ b/player.h
@@ -173,7 +173,7 @@ typedef struct Player {
 
 	PlayerID share_owners[4];
 
-	byte inaugurated_year;
+	Year inaugurated_year;
 	byte num_valid_stat_ent;
 
 	byte quarters_of_bankrupcy;
diff --git a/players.c b/players.c
index d27477c4d..ccfa4b773 100644
--- a/players.c
+++ b/players.c
@@ -490,7 +490,7 @@ Player *DoStartupNewPlayer(bool is_ai)
 	p->share_owners[0] = p->share_owners[1] = p->share_owners[2] = p->share_owners[3] = OWNER_SPECTATOR;
 
 	p->avail_railtypes = GetPlayerRailtypes(p->index);
-	p->inaugurated_year = _cur_year - BASE_YEAR;
+	p->inaugurated_year = _cur_year;
 	p->face = Random();
 
 	/* Engine renewal settings */
@@ -1132,7 +1132,8 @@ static const SaveLoad _player_desc[] = {
 	SLE_CONDVAR(Player, location_of_house,     SLE_UINT32, 6, SL_MAX_VERSION),
 	SLE_CONDVAR(Player, last_build_coordinate, SLE_FILE_U16 | SLE_VAR_U32, 0, 5),
 	SLE_CONDVAR(Player, last_build_coordinate, SLE_UINT32, 6, SL_MAX_VERSION),
-	SLE_VAR(Player,inaugurated_year,SLE_UINT8),
+	SLE_CONDVAR(Player, inaugurated_year,      SLE_FILE_U8  | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Player, inaugurated_year,      SLE_INT32, 31, SL_MAX_VERSION),
 
 	SLE_ARR(Player,share_owners,		SLE_UINT8, 4),
 
diff --git a/saveload.c b/saveload.c
index 7a9f7ba29..8f165e8be 100644
--- a/saveload.c
+++ b/saveload.c
@@ -30,7 +30,7 @@
 #include "variables.h"
 #include <setjmp.h>
 
-const uint16 SAVEGAME_VERSION = 30;
+const uint16 SAVEGAME_VERSION = 31;
 uint16 _sl_version;       /// the major savegame version identifier
 byte   _sl_minor_version; /// the minor savegame version, DO NOT USE!
 
diff --git a/settings.c b/settings.c
index 083bf54c5..098f25763 100644
--- a/settings.c
+++ b/settings.c
@@ -1207,7 +1207,7 @@ static const SettingDescGlobVarList _network_settings[] = {
 	SDTG_BOOL("autoclean_companies",             S, 0, _network_autoclean_companies,  false,       STR_NULL, NULL),
 	 SDTG_VAR("autoclean_unprotected",SLE_UINT8, S, 0, _network_autoclean_unprotected,12, 0,  60,  STR_NULL, NULL),
 	 SDTG_VAR("autoclean_protected",  SLE_UINT8, S, 0, _network_autoclean_protected,  36, 0, 180,  STR_NULL, NULL),
-	 SDTG_VAR("restart_game_year",    SLE_INT16, S,D0, _network_restart_game_year,    0, MIN_YEAR, MAX_YEAR, STR_NULL, NULL),
+	 SDTG_VAR("restart_game_year",    SLE_INT32, S,D0, _network_restart_game_year,    0, MIN_YEAR, MAX_YEAR, STR_NULL, NULL),
 	 SDTG_END()
 };
 #endif /* ENABLE_NETWORK */
@@ -1321,9 +1321,9 @@ const SettingDesc _patch_settings[] = {
 	SDT_BOOL(Patches, same_industry_close,        0, 0, false,            STR_CONFIG_PATCHES_SAMEINDCLOSE,     NULL),
 	SDT_BOOL(Patches, bribe,                      0, 0,  true,            STR_CONFIG_PATCHES_BRIBE,            NULL),
 	 SDT_VAR(Patches, snow_line_height,SLE_UINT8, 0, 0,     7,   2,   13, STR_CONFIG_PATCHES_SNOWLINE_HEIGHT,  NULL),
-	 SDT_VAR(Patches, colored_news_year,SLE_FILE_U32 | SLE_VAR_I16, 0,NC,  2000, MIN_YEAR, MAX_YEAR, STR_CONFIG_PATCHES_COLORED_NEWS_YEAR,NULL),
-	 SDT_VAR(Patches, starting_year,    SLE_FILE_U32 | SLE_VAR_I16, 0,NC,  1950, MIN_YEAR, MAX_YEAR, STR_CONFIG_PATCHES_STARTING_YEAR,NULL),
-	 SDT_VAR(Patches, ending_year,      SLE_FILE_U32 | SLE_VAR_I16,0,NC|NO,2051, MIN_YEAR, MAX_YEAR, STR_CONFIG_PATCHES_ENDING_YEAR,  NULL),
+	 SDT_VAR(Patches, colored_news_year,SLE_INT32, 0,NC,  2000, MIN_YEAR, MAX_YEAR, STR_CONFIG_PATCHES_COLORED_NEWS_YEAR,NULL),
+	 SDT_VAR(Patches, starting_year,    SLE_INT32, 0,NC,  1950, MIN_YEAR, MAX_YEAR, STR_CONFIG_PATCHES_STARTING_YEAR,NULL),
+	 SDT_VAR(Patches, ending_year,      SLE_INT32,0,NC|NO,2051, MIN_YEAR, MAX_YEAR, STR_CONFIG_PATCHES_ENDING_YEAR,  NULL),
 	SDT_BOOL(Patches, smooth_economy,             0, 0,  true,            STR_CONFIG_PATCHES_SMOOTH_ECONOMY,   NULL),
 	SDT_BOOL(Patches, allow_shares,               0, 0,  true,            STR_CONFIG_PATCHES_ALLOW_SHARES,     NULL),
 
@@ -1453,7 +1453,7 @@ const SettingDesc _patch_settings[] = {
 static const SettingDesc _currency_settings[] = {
 	SDT_VAR(CurrencySpec, rate,    SLE_UINT16, S, 0,  1, 0, 100, STR_NULL, NULL),
 	SDT_CHR(CurrencySpec, separator,           S, 0,        ".", STR_NULL, NULL),
-	SDT_VAR(CurrencySpec, to_euro, SLE_UINT16, S, 0,  0, 0,1000, STR_NULL, NULL),
+	SDT_VAR(CurrencySpec, to_euro,  SLE_INT32, S, 0,  0, 0,1000, STR_NULL, NULL),
 	SDT_STR(CurrencySpec, prefix,   SLE_STRBQ, S, 0,       NULL, STR_NULL, NULL),
 	SDT_STR(CurrencySpec, suffix,   SLE_STRBQ, S, 0, " credits", STR_NULL, NULL),
 	SDT_END()
diff --git a/station_cmd.c b/station_cmd.c
index 64503fb7f..71eec64e2 100644
--- a/station_cmd.c
+++ b/station_cmd.c
@@ -3003,7 +3003,8 @@ static const SaveLoad _station_desc[] = {
 
 	// Was custom station class and id
 	SLE_CONDNULL(2, 3, 25),
-	SLE_CONDVAR(Station,build_date,        SLE_UINT16, 3, SL_MAX_VERSION),
+	SLE_CONDVAR(Station,build_date,        SLE_FILE_U16 | SLE_VAR_I32, 3, 30),
+	SLE_CONDVAR(Station,build_date,        SLE_INT32, 31, SL_MAX_VERSION),
 
 	SLE_CONDREF(Station,bus_stops,         REF_ROADSTOPS, 6, SL_MAX_VERSION),
 	SLE_CONDREF(Station,truck_stops,       REF_ROADSTOPS, 6, SL_MAX_VERSION),
diff --git a/vehicle.c b/vehicle.c
index 0c0edc92e..9e10c9f81 100644
--- a/vehicle.c
+++ b/vehicle.c
@@ -2202,17 +2202,22 @@ const SaveLoad _common_veh_desc[] = {
 
 	SLE_REF(Vehicle,orders,						REF_ORDER),
 
-	SLE_VAR(Vehicle,age,							SLE_UINT16),
-	SLE_VAR(Vehicle,max_age,					SLE_UINT16),
-	SLE_VAR(Vehicle,date_of_last_service,SLE_UINT16),
-	SLE_VAR(Vehicle,service_interval,	SLE_UINT16),
+	SLE_CONDVAR(Vehicle,age,					SLE_FILE_U16 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Vehicle,age,					SLE_INT32, 31, SL_MAX_VERSION),
+	SLE_CONDVAR(Vehicle,max_age,			SLE_FILE_U16 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Vehicle,max_age,			SLE_INT32, 31, SL_MAX_VERSION),
+	SLE_CONDVAR(Vehicle,date_of_last_service,	SLE_FILE_U16 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Vehicle,date_of_last_service,	SLE_INT32, 31, SL_MAX_VERSION),
+	SLE_CONDVAR(Vehicle,service_interval,			SLE_FILE_U16 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Vehicle,service_interval,			SLE_INT32, 31, SL_MAX_VERSION),
 	SLE_VAR(Vehicle,reliability,			SLE_UINT16),
 	SLE_VAR(Vehicle,reliability_spd_dec,SLE_UINT16),
 	SLE_VAR(Vehicle,breakdown_ctr,		SLE_UINT8),
 	SLE_VAR(Vehicle,breakdown_delay,	SLE_UINT8),
 	SLE_VAR(Vehicle,breakdowns_since_last_service,	SLE_UINT8),
 	SLE_VAR(Vehicle,breakdown_chance,	SLE_UINT8),
-	SLE_VAR(Vehicle,build_year,				SLE_UINT8),
+	SLE_CONDVAR(Vehicle,build_year,		SLE_FILE_U8 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Vehicle,build_year,		SLE_INT32, 31, SL_MAX_VERSION),
 
 	SLE_VAR(Vehicle,load_unload_time_rem,	SLE_UINT16),
 
@@ -2362,8 +2367,8 @@ static const SaveLoad _disaster_desc[] = {
 	SLE_CONDVARX(offsetof(Vehicle, current_order) + offsetof(Order, station), SLE_UINT16, 5, SL_MAX_VERSION),
 
 	SLE_VAR(Vehicle,cur_image,				SLE_UINT16),
-	SLE_VAR(Vehicle,age,							SLE_UINT16),
-
+	SLE_CONDVAR(Vehicle,age,					SLE_FILE_U16 | SLE_VAR_I32, 0, 30),
+	SLE_CONDVAR(Vehicle,age,					SLE_INT32, 31, SL_MAX_VERSION),
 	SLE_VAR(Vehicle,tick_counter,			SLE_UINT8),
 
 	SLE_VARX(offsetof(Vehicle,u)+offsetof(VehicleDisaster,image_override),	SLE_UINT16),
diff --git a/vehicle.h b/vehicle.h
index 26750e35f..86c9ffa87 100644
--- a/vehicle.h
+++ b/vehicle.h
@@ -208,8 +208,8 @@ struct Vehicle {
 	VehicleID next_hash;
 
 	// Related to age and service time
-	uint16 age;				// Age in days
-	uint16 max_age;		// Maximum age
+	Date age;     // Age in days
+	Date max_age; // Maximum age
 	Date date_of_last_service;
 	Date service_interval;
 	uint16 reliability;
@@ -218,7 +218,7 @@ struct Vehicle {
 	byte breakdown_delay;
 	byte breakdowns_since_last_service;
 	byte breakdown_chance;
-	byte build_year;
+	Year build_year;
 
 	bool leave_depot_instantly;	// NOSAVE: stores if the vehicle needs to leave the depot it just entered. Used by autoreplace
 
diff --git a/waypoint.c b/waypoint.c
index 4d0b9a519..b946d38c4 100644
--- a/waypoint.c
+++ b/waypoint.c
@@ -408,7 +408,8 @@ static const SaveLoad _waypoint_desc[] = {
 	SLE_VAR(Waypoint, string, SLE_UINT16),
 	SLE_VAR(Waypoint, deleted, SLE_UINT8),
 
-	SLE_CONDVAR(Waypoint, build_date, SLE_UINT16,  3, SL_MAX_VERSION),
+	SLE_CONDVAR(Waypoint, build_date, SLE_FILE_U16 | SLE_VAR_I32, 3, 30),
+	SLE_CONDVAR(Waypoint, build_date, SLE_INT32,  31, SL_MAX_VERSION),
 	SLE_CONDVAR(Waypoint, localidx,   SLE_UINT8,   3, SL_MAX_VERSION),
 	SLE_CONDVAR(Waypoint, grfid,      SLE_UINT32, 17, SL_MAX_VERSION),