kernel/mktime.c

   1 /*
   2  *  linux/kernel/mktime.c
   3  *
   4  *  (C) 1991  Linus Torvalds
   5  */
   6
   7 #include <time.h>
   8
   9 /*
  10  * This isn't the library routine, it is only used in the kernel.
  11  * as such, we don't care about years<1970 etc, but assume everything
  12  * is ok. Similarly, TZ etc is happily ignored. We just do everything
  13  * as easily as possible. Let's find something public for the library
  14  * routines (although I think minix times is public).
  15  */
  16 /*
  17  * PS. I hate whoever though up the year 1970 - couldn't they have gotten
  18  * a leap-year instead? I also hate Gregorius, pope or no. I'm grumpy.
  19  */
  20 #define MINUTE 60
  21 #define HOUR (60*MINUTE)
  22 #define DAY (24*HOUR)
  23 #define YEAR (365*DAY)
  24
  25 /* interestingly, we assume leap-years */
  26 static int month[12] = {
  27         0,
  28         DAY*(31),
  29         DAY*(31+29),
  30         DAY*(31+29+31),
  31         DAY*(31+29+31+30),
  32         DAY*(31+29+31+30+31),
  33         DAY*(31+29+31+30+31+30),
  34         DAY*(31+29+31+30+31+30+31),
  35         DAY*(31+29+31+30+31+30+31+31),
  36         DAY*(31+29+31+30+31+30+31+31+30),
  37         DAY*(31+29+31+30+31+30+31+31+30+31),
  38         DAY*(31+29+31+30+31+30+31+31+30+31+30)
  39 };
  40
  41 long kernel_mktime(struct tm * tm)
  42 {
  43         long res;
  44         int year;
  45
  46         year = tm->tm_year - 70;
  47 /* magic offsets (y+1) needed to get leapyears right.*/
  48         res = YEAR*year + DAY*((year+1)/4);
  49         res += month[tm->tm_mon];
  50 /* and (y+2) here. If it wasn't a leap-year, we have to adjust */
  51         if (tm->tm_mon>1 && ((year+2)%4))
  52                 res -= DAY;
  53         res += DAY*(tm->tm_mday-1);
  54         res += HOUR*tm->tm_hour;
  55         res += MINUTE*tm->tm_min;
  56         res += tm->tm_sec;
  57         return res;
  58 }