Diff: time.cpp

Revision:

8:45a0205a298f

Parent:

7:024ace6d943c

--- a/time.cpp	Thu Jun 02 09:26:28 2016 +0000
+++ b/time.cpp	Thu Dec 06 11:40:19 2018 +0000
@@ -33,18 +33,14 @@
     //Add a year at a time while there is more than a year of days left
     int year      = 1970; //Unix epoch is 1970
     int dayOfWeek = 4;    //1 Jan 1970 is a Thursday
-    int dayOfYear;
     int leapYear;
     while(1)
     {
         //See if it is a leap year
-        int year4   = !(year %   4);
-        int year100 = !(year % 100);
-        int year400 = !(year % 400);
-                     leapYear = false;
-        if (year4)   leapYear =  true;
-        if (year100) leapYear = false;
-        if (year400) leapYear =  true;
+                             leapYear = false;
+        if (year %   4 == 0) leapYear =  true;
+        if (year % 100 == 0) leapYear = false;
+        if (year % 400 == 0) leapYear =  true;
         
         //Find the number of days in this year
         int daysInYear = leapYear ? 366 : 365;
@@ -61,30 +57,18 @@
         year++;
     }
     
-    dayOfYear = daysLeft;
+    //Days left contains the days left from the start (1 Jan) of the current year
+    int dayOfYear = daysLeft + 1;
     dayOfWeek += daysLeft;
     dayOfWeek %= 7;
 
     //Add a month at a time while there is more than a month of days left
-    int month = 0;
+    static char monthlengths[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+    int month = 1;
     while(1)
     {
-        int daysInMonth;
-        switch (month + 1)
-        {
-            case  1: daysInMonth = 31; break;
-            case  2: daysInMonth = leapYear ? 29 : 28; break;
-            case  3: daysInMonth = 31; break;
-            case  4: daysInMonth = 30; break;
-            case  5: daysInMonth = 31; break;
-            case  6: daysInMonth = 30; break;
-            case  7: daysInMonth = 31; break;
-            case  8: daysInMonth = 31; break;
-            case  9: daysInMonth = 30; break;
-            case 10: daysInMonth = 31; break;
-            case 11: daysInMonth = 30; break;
-            case 12: daysInMonth = 31; break;
-        }
+        int daysInMonth = monthlengths[month-1];
+        if (month == 2 && leapYear) daysInMonth++;
         
         //Stop if this is the last month
         if (daysLeft < daysInMonth) break;
@@ -93,15 +77,49 @@
         daysLeft -= daysInMonth;
         month++;
     }
-
-  ptm->tm_sec  = seconds;
-  ptm->tm_min  = minutes;
-  ptm->tm_hour = hours;
-  ptm->tm_mday = daysLeft + 1;
-  ptm->tm_mon  = month;
-  ptm->tm_year = year - 1900;
-  ptm->tm_wday = dayOfWeek;
-  ptm->tm_yday = dayOfYear;
+    
+    //Days left contains the days left from the start (1st) of the current month
+    int dayOfMonth = daysLeft + 1;
+      
+    //Find the last Sunday in the month
+    int lastSunday = monthlengths[month-1];
+    while (lastSunday > 0)
+    {
+        int weekday = (dayOfWeek + lastSunday - dayOfMonth) % 7;
+        if (weekday == 0) break; //Stop when weekday is Sunday
+        lastSunday--;
+    }
+    
+    //Work out if Daylight Saving Time applies
+    int dst;
+    if (month <= 2) dst = false;              //Jan, Feb
+    if (month == 3)                           //Mar - DST true after 1am UTC on the last Sunday in March
+    {
+        if (dayOfMonth <  lastSunday) dst = false;
+        if (dayOfMonth == lastSunday) dst = hours >= 1;
+        if (dayOfMonth >  lastSunday) dst = true;
+    }
+    if (month >= 4 && month <= 9) dst = true; //Apr, May, Jun, Jul, Aug, Sep
+    if (month == 10)                          //Oct - DST false after 1am UTC on the last Sunday in October
+    {
+        if (dayOfMonth <  lastSunday) dst = true;
+        if (dayOfMonth == lastSunday) dst = hours < 1;
+        if (dayOfMonth >  lastSunday) dst = false;
+    }
+    if (month >= 11) dst = false;             //Nov, Dec
+    
+    
+    //Set up the broken time TM structure
+    ptm->tm_sec   = seconds;       // 00 --> 59
+    ptm->tm_min   = minutes;       // 00 --> 59
+    ptm->tm_hour  = hours;         // 00 --> 23
+    ptm->tm_mday  = dayOfMonth;    // 01 --> 31
+    ptm->tm_mon   = month - 1;     // 00 --> 11
+    ptm->tm_year  = year - 1900;   // Years since 1900
+    ptm->tm_wday  = dayOfWeek;     // 0 --> 6 where 0 == Sunday
+    ptm->tm_yday  = dayOfYear - 1; // 0 --> 365
+    ptm->tm_isdst = dst;           // +ve if DST, 0 if not DSTime, -ve if the information is not available. Note that 'true' evaluates to +1.
+    
 }
 void TimeGetTm(struct tm* ptm)
 {