ref: 87bd72ba5cbafb99c58e608c335705a98b10ce23
dir: /libc/ctime.c/
/*
* This routine converts time as follows.
* The epoch is 0000 Jan 1 1970 GMT.
* The argument time is in seconds since then.
* The localtime(t) entry returns a pointer to an array
* containing
*
* seconds (0-59)
* minutes (0-59)
* hours (0-23)
* day of month (1-31)
* month (0-11)
* year-1970
* weekday (0-6, Sun is 0)
* day of the year
* daylight savings flag
*
* The routine gets the daylight savings time from the environment.
*
* asctime(tvec))
* where tvec is produced by localtime
* returns a ptr to a character string
* that has the ascii time in the form
*
* \\
* Thu Jan 01 00:00:00 GMT 1970n0
* 012345678901234567890123456789
* 0 1 2
*
* ctime(t) just calls localtime, then asctime.
*/
#include <u.h>
#include <libc.h>
static char dmsize[12] =
{
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};
/*
* The following table is used for 1974 and 1975 and
* gives the day number of the first day after the Sunday of the
* change.
*/
#define dysize _dysize /* conflicts on unix */
static int
dysize(int y)
{
if(y%4 == 0 && (y%100 != 0 || y%400 == 0))
return 366;
return 365;
}
Tm*
gmtime(long tim)
{
int d0, d1;
long hms, day;
static Tm xtime;
/*
* break initial number into days
*/
hms = tim % 86400L;
day = tim / 86400L;
if(hms < 0) {
hms += 86400L;
day -= 1;
}
/*
* generate hours:minutes:seconds
*/
xtime.sec = hms % 60;
d1 = hms / 60;
xtime.min = d1 % 60;
d1 /= 60;
xtime.hour = d1;
/*
* day is the day number.
* generate day of the week.
* The addend is 4 mod 7 (1/1/1970 was Thursday)
*/
xtime.wday = (day + 7340036L) % 7;
/*
* year number
*/
if(day >= 0)
for(d1 = 1970; day >= dysize(d1); d1++)
day -= dysize(d1);
else
for (d1 = 1970; day < 0; d1--)
day += dysize(d1-1);
xtime.year = d1-1900;
xtime.yday = d0 = day;
/*
* generate month
*/
if(dysize(d1) == 366)
dmsize[1] = 29;
for(d1 = 0; d0 >= dmsize[d1]; d1++)
d0 -= dmsize[d1];
dmsize[1] = 28;
xtime.mday = d0 + 1;
xtime.mon = d1;
strcpy(xtime.zone, "GMT");
return &xtime;
}