Speed up RtlTimeToTimeFields.

diff --git a/dlls/ntdll/time.c b/dlls/ntdll/time.c
index b88ff8faaafc1111b8f4e966f633fd8f99345e5f..bd10c5085545e1b530c183fe45df4561dd802638 100644 (file)
--- a/dlls/ntdll/time.c
+++ b/dlls/ntdll/time.c
@@ -272,6 +272,9 @@ static const struct tagTZ_INFO TZ_INFO[] =
 #define DAYSPERNORMALYEAR  365
 #define DAYSPERLEAPYEAR    366
 #define MONSPERYEAR        12
+#define DAYSPERQUADRICENTENNIUM (365 * 400 + 97)
+#define DAYSPERNORMALCENTURY (365 * 100 + 24)
+#define DAYSPERNORMALQUADRENNIUM (365 * 4 + 1)
 
 /* 1601 to 1970 is 369 years plus 89 leap days */
 #define SECS_1601_TO_1970  ((369 * 365 + 89) * (ULONGLONG)SECSPERDAY)
@@ -350,7 +353,7 @@ VOID WINAPI RtlTimeToTimeFields(
        PTIME_FIELDS TimeFields)
 {
        const int *Months;
-       int SecondsInDay, CurYear;
+       int SecondsInDay, DeltaYear;
        int LeapYear, CurMonth;
        long int Days;
        LONGLONG Time = liTime->QuadPart;
@@ -376,17 +379,22 @@ VOID WINAPI RtlTimeToTimeFields(
        TimeFields->Weekday = (CSHORT) ((EPOCHWEEKDAY + Days) % DAYSPERWEEK);
 
        /* compute year */
-       CurYear = EPOCHYEAR;
        /* FIXME: handle calendar modifications */
-       while (1)
-       { LeapYear = IsLeapYear(CurYear);
-         if (Days < (long) YearLengths[LeapYear])
-         { break;
-         }
-         CurYear++;
-         Days = Days - (long) YearLengths[LeapYear];
-       }
-       TimeFields->Year = (CSHORT) CurYear;
+        TimeFields->Year = EPOCHYEAR;
+        DeltaYear = Days / DAYSPERQUADRICENTENNIUM;
+        TimeFields->Year += DeltaYear * 400;
+        Days -= DeltaYear * DAYSPERQUADRICENTENNIUM;
+        DeltaYear = Days / DAYSPERNORMALCENTURY;
+        TimeFields->Year += DeltaYear * 100;
+        Days -= DeltaYear * DAYSPERNORMALCENTURY;
+        DeltaYear = Days / DAYSPERNORMALQUADRENNIUM;
+        TimeFields->Year += DeltaYear * 4;
+        Days -= DeltaYear * DAYSPERNORMALQUADRENNIUM;
+        DeltaYear = Days / DAYSPERNORMALYEAR;
+        TimeFields->Year += DeltaYear;
+        Days -= DeltaYear * DAYSPERNORMALYEAR;
+
+        LeapYear = IsLeapYear(TimeFields->Year);
 
        /* Compute month of year */
        Months = MonthLengths[LeapYear];