(svn r5975) -Cleanup: use ORIGINAL_BASE_YEAR & ORIGINAL_MAX_YEAR where the functions really depend on the original date format.

-Cleanup: use DAYS_TILL_ORIGINAL_BASE_YEAR where the date variables are in the old date format and conversions are needed.
-Cleanup: replace one (forgotten) instance of uint16 with Date.

7 files changed, 30 insertions, 9 deletions

diff --git a/ai/default/default.c b/ai/default/default.c
index 752d2cac9..54a550599 100644
--- a/ai/default/default.c
+++ b/ai/default/default.c
@@ -1457,7 +1457,7 @@ static void AiWantAircraftRoute(Player *p)
 {
 	uint16 r = (uint16)Random();
 
-	if (r >= 0x2AAA || _date < 0x3912) {
+	if (r >= 0x2AAA || _date < 0x3912 + DAYS_TILL_ORIGINAL_BASE_YEAR) {
 		AiWantPassengerAircraftRoute(p);
 	} else {
 		AiWantOilRigAircraftRoute(p);
diff --git a/date.h b/date.h
index 8ca64ece2..1b5288599 100644
--- a/date.h
+++ b/date.h
@@ -8,7 +8,28 @@
  */
 #define DAY_TICKS 74
 
+/*
+ * ORIGINAL_BASE_YEAR, ORIGINAL_MAX_YEAR and DAYS_TILL_ORIGINAL_BASE_YEAR are
+ * primarily used for loading newgrf and savegame data and returning some
+ * newgrf (callback) functions that were in the original (TTD) inherited
+ * format, where '_date == 0' meant that it was 1920-01-01.
+ */
+
+/** The minimum starting year/base year of the original TTD */
+#define ORIGINAL_BASE_YEAR 1920
+/** The maximum year of the original TTD */
+#define ORIGINAL_MAX_YEAR 2090
+
+/**
+ * The offset in days from the '_date == 0' till
+ * 'ConvertYMDToDate(ORIGINAL_BASE_YEAR, 0, 1)'
+ */
+#define DAYS_TILL_ORIGINAL_BASE_YEAR 0
+
+/* Temporary value to make transition to full past 2090 easier/more clear */
 #define BASE_YEAR 1920
+
+/* The absolute minimum & maximum years in OTTD */
 #define MIN_YEAR 1920
 #define MAX_YEAR 2090
 
diff --git a/engine.c b/engine.c
index bd7e72a3b..ceaa91fb4 100644
--- a/engine.c
+++ b/engine.c
@@ -6,7 +6,6 @@
 #include "functions.h"
 #include "table/strings.h"
 #include "engine.h"
-#include "table/engines.h"
 #include "gfx.h"
 #include "player.h"
 #include "command.h"
@@ -17,6 +16,7 @@
 #include "train.h"
 #include "newgrf_cargo.h"
 #include "date.h"
+#include "table/engines.h"
 
 EngineInfo _engine_info[TOTAL_NUM_ENGINES];
 RailVehicleInfo _rail_vehicle_info[NUM_TRAIN_ENGINES];
@@ -140,7 +140,7 @@ void StartupEngines(void)
 	Engine *e;
 	const EngineInfo *ei;
 	/* Aging of vehicles stops, so account for that when starting late */
-	const uint16 aging_date = min(_date, ConvertYMDToDate(YEAR_ENGINE_AGING_STOPS, 0, 1));
+	const Date aging_date = min(_date, ConvertYMDToDate(YEAR_ENGINE_AGING_STOPS, 0, 1));
 
 	SetupEngineNames();
 
diff --git a/newgrf.c b/newgrf.c
index 27a31e608..cd2e99acf 100644
--- a/newgrf.c
+++ b/newgrf.c
@@ -1007,7 +1007,7 @@ static bool BridgeChangeInfo(uint brid, int numinfo, int prop, byte **bufp, int
 
 	switch (prop) {
 		case 0x08: /* Year of availability */
-			FOR_EACH_OBJECT _bridge[brid + i].avail_year = BASE_YEAR + grf_load_byte(&buf);
+			FOR_EACH_OBJECT _bridge[brid + i].avail_year = ORIGINAL_BASE_YEAR + grf_load_byte(&buf);
 			break;
 
 		case 0x09: /* Minimum length */
@@ -1177,7 +1177,7 @@ static void FeatureChangeInfo(byte *buf, int len)
 				/* Common properties for vehicles */
 				switch (prop) {
 					case 0x00: /* Introduction date */
-						FOR_EACH_OBJECT ei[i].base_intro = grf_load_word(&buf);
+						FOR_EACH_OBJECT ei[i].base_intro = grf_load_word(&buf) + DAYS_TILL_ORIGINAL_BASE_YEAR;
 						break;
 
 					case 0x02: /* Decay speed */
diff --git a/newgrf_engine.c b/newgrf_engine.c
index 90b7f1e82..8413770d5 100644
--- a/newgrf_engine.c
+++ b/newgrf_engine.c
@@ -553,7 +553,7 @@ static uint32 VehicleGetVariable(const ResolverObject *object, byte variable, by
 			case 0x43: return _current_player; /* Owner information */
 			case 0x46: return 0;               /* Motion counter */
 			case 0x48: return GetVehicleTypeInfo(object->u.vehicle.self_type); /* Vehicle Type Info */
-			case 0xC4: return clamp(_cur_year, BASE_YEAR, MAX_YEAR) - BASE_YEAR; /* Build year */
+			case 0xC4: return clamp(_cur_year, ORIGINAL_BASE_YEAR, ORIGINAL_MAX_YEAR) - ORIGINAL_BASE_YEAR; /* Build year */
 			case 0xDA: return INVALID_VEHICLE; /* Next vehicle */
 			case 0x7F: return GetGRFParameter(object->u.vehicle.self_type, parameter); /* Read GRF parameter */
 		}
diff --git a/newgrf_spritegroup.c b/newgrf_spritegroup.c
index f6e0e37bb..601116e7a 100644
--- a/newgrf_spritegroup.c
+++ b/newgrf_spritegroup.c
@@ -76,7 +76,7 @@ static inline uint32 GetVariable(const ResolverObject *object, byte variable, by
 	/* Return common variables */
 	switch (variable) {
 		case 0x00: return _date;
-		case 0x01: return clamp(_cur_year, BASE_YEAR, MAX_YEAR) - BASE_YEAR;
+		case 0x01: return clamp(_cur_year, ORIGINAL_BASE_YEAR, ORIGINAL_MAX_YEAR) - ORIGINAL_BASE_YEAR;
 		case 0x02: return _cur_month;
 		case 0x03: return _opt.landscape;
 		case 0x09: return _date_fract;
diff --git a/table/engines.h b/table/engines.h
index 9365c7f8c..f468f0029 100644
--- a/table/engines.h
+++ b/table/engines.h
@@ -15,7 +15,7 @@
   * @param e Rail Type of the vehicle
   * @param f Bitmask of the climates
   */
-#define MK(a, b, c, d, e, f) { a, b, c, d, e, f, 0, 8, 0, 0 }
+#define MK(a, b, c, d, e, f) { DAYS_TILL_ORIGINAL_BASE_YEAR + a, b, c, d, e, f, 0, 8, 0, 0 }
 /** Writes the properties of a train carriage into the EngineInfo struct.
   * @see EngineInfo
   * @param a Introduction date
@@ -23,7 +23,7 @@
   * @param f Bitmask of the climates
   * @note the 0x80 in parameter b sets the "is carriage bit"
   */
-#define MW(a, b, c, d, e, f) { a, b | 0x80, c, d, e, f, 0, 8, 0, 0 }
+#define MW(a, b, c, d, e, f) { DAYS_TILL_ORIGINAL_BASE_YEAR + a, b | 0x80, c, d, e, f, 0, 8, 0, 0 }
 
 // Rail types
 // R = Conventional railway