localt~1.c

来自「操作系统源代码」· C语言 代码 · 共 35 行

/*
 * localtime - convert a calendar time into broken down time
 */
/* $Header: localtime.c,v 1.3 91/04/22 13:20:36 ceriel Exp $ */

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

/* We must be careful, since an int can't represent all the seconds in a day.
 * Hence the adjustment of minutes when adding timezone and dst information.
 * This assumes that both must be expressable in multiples of a minute.
 * Furthermore, it is assumed that both fit into an integer when expressed as
 * minutes (this is about 22 days, so this should not cause any problems). 
 */
struct tm *
localtime(const time_t *timer)
{
	struct tm *timep;
	unsigned dst;

	_tzset();
	timep = gmtime(timer);			/* tm->tm_isdst == 0 */
	timep->tm_min -= _timezone / 60;
	timep->tm_sec -= _timezone % 60;
	mktime(timep);

	dst = _dstget(timep);
	if (dst) {
		timep->tm_min += dst / 60;
		timep->tm_sec += dst % 60;
		mktime(timep);
	}
	return timep;
}