gmtime.c

来自「操作系统源代码」· C语言 代码 · 共 42 行

/*
 * gmtime - convert the calendar time into broken down time
 */
/* $Header: gmtime.c,v 1.4 91/04/22 13:20:27 ceriel Exp $ */

#include	<time.h>
#include	<limits.h>
#include	"loc_time.h"

struct tm *
gmtime(register const time_t *timer)
{
	static struct tm br_time;
	register struct tm *timep = &br_time;
	time_t time = *timer;
	register unsigned long dayclock, dayno;
	int year = EPOCH_YR;

	dayclock = (unsigned long)time % SECS_DAY;
	dayno = (unsigned long)time / SECS_DAY;

	timep->tm_sec = dayclock % 60;
	timep->tm_min = (dayclock % 3600) / 60;
	timep->tm_hour = dayclock / 3600;
	timep->tm_wday = (dayno + 4) % 7;	/* day 0 was a thursday */
	while (dayno >= YEARSIZE(year)) {
		dayno -= YEARSIZE(year);
		year++;
	}
	timep->tm_year = year - YEAR0;
	timep->tm_yday = dayno;
	timep->tm_mon = 0;
	while (dayno >= _ytab[LEAPYEAR(year)][timep->tm_mon]) {
		dayno -= _ytab[LEAPYEAR(year)][timep->tm_mon];
		timep->tm_mon++;
	}
	timep->tm_mday = dayno + 1;
	timep->tm_isdst = 0;

	return timep;
}