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//without using any header file
// Tried without using any files.
#include <stdio.h>
//#include <string.h>
//#include <time.h>
typedef unsigned uint;
typedef unsigned long long uint64;
struct tm {
int tm_sec; /* seconds, range 0 to 59 */
int tm_min; /* minutes, range 0 to 59 */
int tm_hour; /* hours, range 0 to 23 */
int tm_mday; /* day of the month, range 1 to 31 */
int tm_mon; /* month, range 0 to 11 */
int tm_year; /* The number of years since 1900 */
int tm_wday; /* day of the week, range 0 to 6 */
int tm_yday; /* day in the year, range 0 to 365 */
int tm_isdst; /* daylight saving time */
};
extern char *asctime(const struct tm *timeptr)
{
static char wday_name[7][3] = {
"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
static char mon_name[12][3] = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
static char result[26];
sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
wday_name[timeptr->tm_wday],
mon_name[timeptr->tm_mon],
timeptr->tm_mday, timeptr->tm_hour,
timeptr->tm_min, timeptr->tm_sec,
1900 + timeptr->tm_year);
return result;
}
struct tm* SecondsSinceEpochToDateTime(struct tm* pTm, uint64 SecondsSinceEpoch)
{
uint64 sec;
uint quadricentennials, centennials, quadrennials, annuals/*1-ennial?*/;
uint year, leap;
uint yday, hour, min;
uint month, mday, wday;
static const uint daysSinceJan1st[2][13]=
{
{0,31,59,90,120,151,181,212,243,273,304,334,365}, // 365 days, non-leap
{0,31,60,91,121,152,182,213,244,274,305,335,366} // 366 days, leap
};
/*
400 years:
1st hundred, starting immediately after a leap year that's a multiple of 400:
n n n l \
n n n l } 24 times
... /
n n n l /
n n n n
2nd hundred:
n n n l \
n n n l } 24 times
... /
n n n l /
n n n n
3rd hundred:
n n n l \
n n n l } 24 times
... /
n n n l /
n n n n
4th hundred:
n n n l \
n n n l } 24 times
... /
n n n l /
n n n L <- 97'th leap year every 400 years
*/
// Re-bias from 1970 to 1601:
// 1970 - 1601 = 369 = 3*100 + 17*4 + 1 years (incl. 89 leap days) =
// (3*100*(365+24/100) + 17*4*(365+1/4) + 1*365)*24*3600 seconds
sec = SecondsSinceEpoch + 11644473600;
wday = (uint)((sec / 86400 + 1) % 7); // day of week
// Remove multiples of 400 years (incl. 97 leap days)
quadricentennials = (uint)(sec / 12622780800ULL); // 400*365.2425*24*3600
sec %= 12622780800ULL;
// Remove multiples of 100 years (incl. 24 leap days), can't be more than 3
// (because multiples of 4*100=400 years (incl. leap days) have been removed)
centennials = (uint)(sec / 3155673600ULL); // 100*(365+24/100)*24*3600
if (centennials > 3)
{
centennials = 3;
}
sec -= centennials * 3155673600ULL;
// Remove multiples of 4 years (incl. 1 leap day), can't be more than 24
// (because multiples of 25*4=100 years (incl. leap days) have been removed)
quadrennials = (uint)(sec / 126230400); // 4*(365+1/4)*24*3600
if (quadrennials > 24)
{
quadrennials = 24;
}
sec -= quadrennials * 126230400ULL;
// Remove multiples of years (incl. 0 leap days), can't be more than 3
// (because multiples of 4 years (incl. leap days) have been removed)
annuals = (uint)(sec / 31536000); // 365*24*3600
if (annuals > 3)
{
annuals = 3;
}
sec -= annuals * 31536000ULL;
// Calculate the year and find out if it's leap
year = 1601 + quadricentennials * 400 + centennials * 100 + quadrennials * 4 + annuals;
leap = !(year % 4) && (year % 100 || !(year % 400));
// Calculate the day of the year and the time
yday = sec / 86400;
sec %= 86400;
hour = sec / 3600;
sec %= 3600;
min = sec / 60;
sec %= 60;
// Calculate the month
for (mday = month = 1; month < 13; month++)
{
if (yday < daysSinceJan1st[leap][month])
{
mday += yday - daysSinceJan1st[leap][month - 1];
break;
}
}
// Fill in C's "struct tm"
memset(pTm, 0, sizeof(*pTm));
pTm->tm_sec = sec; // [0,59]
pTm->tm_min = min; // [0,59]
pTm->tm_hour = hour; // [0,23]
pTm->tm_mday = mday; // [1,31] (day of month)
pTm->tm_mon = month - 1; // [0,11] (month)
pTm->tm_year = year - 1900; // 70+ (year since 1900)
pTm->tm_wday = wday; // [0,6] (day since Sunday AKA day of week)
pTm->tm_yday = yday; // [0,365] (day since January 1st AKA day of year)
pTm->tm_isdst = -1; // daylight saving time flag
return pTm;
}
int main(void)
{
struct tm t;
//time_t tt;
printf("%s", asctime(SecondsSinceEpochToDateTime(&t, -1)));
//printf("%s", asctime(gmtime((tt = 0, &tt))));
printf("%s", asctime(SecondsSinceEpochToDateTime(&t, 0)));
printf("%s\n", asctime(SecondsSinceEpochToDateTime(&t, 1)));
printf("%s", asctime(SecondsSinceEpochToDateTime(&t, 946684799)));
printf("%s", asctime(SecondsSinceEpochToDateTime(&t, 946684799+1)));
printf("%s\n", asctime(SecondsSinceEpochToDateTime(&t, 946684799+2)));
printf("%s", asctime(SecondsSinceEpochToDateTime(&t, 978307199)));
printf("%s", asctime(SecondsSinceEpochToDateTime(&t, 978307199+1)));
printf("%s\n", asctime(SecondsSinceEpochToDateTime(&t, 1399481439)));
//printf("%s", asctime(SecondsSinceEpochToDateTime(&t, tt = time(0))));
//printf("%s", asctime(gmtime(&tt)));
return 0;
}