(svn r18291) -Codechange: rework the calculation of the 'days till year' macro a bit so it can be properly reused and add a MAX_DAY

1 files changed, 31 insertions, 4 deletions

diff --git a/src/date_type.h b/src/date_type.h
index 9817e1e2f..ae92b1d27 100644
--- a/src/date_type.h
+++ b/src/date_type.h
@@ -39,17 +39,44 @@ enum {
 #define ORIGINAL_MAX_YEAR 2090
 
 /**
+ * Calculate the number of leap years till a given year.
+ *
+ * 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.
+ *
+ * @param year the year to get the leap years till.
+ * @return the number of leap years.
+ */
+#define LEAP_YEARS_TILL(year) ((year) == 0 ? 0 : ((year) - 1) / 4 - ((year) - 1) / 100 + ((year) - 1) / 400 + 1)
+
+/**
+ * Calculate the date of the first day of a given year.
+ * @param year the year to get the first day of.
+ * @return the date.
+ */
+#define DAYS_TILL(year) (DAYS_IN_YEAR * (year) + LEAP_YEARS_TILL(year))
+
+/**
  * The offset in days from the '_date == 0' till
  * 'ConvertYMDToDate(ORIGINAL_BASE_YEAR, 0, 1)'
  */
-#define DAYS_TILL_ORIGINAL_BASE_YEAR (DAYS_IN_YEAR * ORIGINAL_BASE_YEAR + ORIGINAL_BASE_YEAR / 4 - ORIGINAL_BASE_YEAR / 100 + ORIGINAL_BASE_YEAR / 400)
+#define DAYS_TILL_ORIGINAL_BASE_YEAR DAYS_TILL(ORIGINAL_BASE_YEAR)
 
-/* The absolute minimum & maximum years in OTTD */
+/** The absolute minimum & maximum years in OTTD */
 #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. */
+
+/**
+ * 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
 
+/** The number of days till the last day */
+#define MAX_DAY DAYS_TILL(MAX_YEAR + 1) - 1
+
 typedef int32  Date;      ///< The type to store our dates in
 typedef uint16 DateFract; ///< The fraction of a date we're in, i.e. the number of ticks since the last date changeover
 typedef int32  Ticks;     ///< The type to store ticks in