uclibc-ng/libc/misc/time/tm_conv.c

#if 0
#include <time.h>

/* This is a translation from ALGOL in Collected Algorithms of CACM. */
/* Copied from Algorithm 199, Author: Robert G. Tantzen */

void __tm_conv(tmbuf, timep, offset)
struct tm *tmbuf;
time_t *timep;
time_t offset;
{
	static int moffset[] =
		{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };

	long s;
	long j, d, m, y;

	offset += *timep;

	tmbuf->tm_isdst = 0;		/* Someone else can set this */

	j = offset / 86400L + 719469;
	s = offset % 86400L;

	if (s < 0) {
		s += 86400L;
		j--;
	}

	tmbuf->tm_sec = s % 60;
	tmbuf->tm_min = (s / 60) % 60;
	tmbuf->tm_hour = s / 3600;

	tmbuf->tm_wday = (j + 2) % 7;

	/*
	 * Julian date converter. Takes a julian date (the number of days since
	 * some distant epoch or other), and fills tmbuf.
	 */

	y = (4L * j - 1L) / 146097L;
	j = 4L * j - 1L - 146097L * y;
	d = j / 4L;
	j = (4L * d + 3L) / 1461L;
	d = 4L * d + 3L - 1461L * j;
	d = (d + 4L) / 4L;
	m = (5L * d - 3L) / 153L;
	d = 5L * d - 3 - 153L * m;
	d = (d + 5L) / 5L;
	y = 100L * y + j;
	if (m < 10)
		m += 2;
	else {
		m -= 10;
		++y;
	}

	tmbuf->tm_year = y - 1900;
	tmbuf->tm_mon = m;
	tmbuf->tm_mday = d;

	tmbuf->tm_yday = d + moffset[m];
	if (m > 1 && ((y) % 4 == 0 && ((y) % 100 != 0 || (y) % 400 == 0)))
		tmbuf->tm_yday++;
}

#else

/* This is adapted from glibc */
/* Copyright (C) 1991, 1993 Free Software Foundation, Inc */

#define SECS_PER_HOUR 3600L
#define SECS_PER_DAY  86400L

#include <time.h>

static const unsigned short int __mon_lengths[2][12] = {
	/* Normal years.  */
	{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
	/* Leap years.  */
	{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};


void __tm_conv(tmbuf, t, offset)
struct tm *tmbuf;
time_t *t;
time_t offset;
{
	long days, rem;
	register int y;
	register const unsigned short int *ip;

	days = *t / SECS_PER_DAY;
	rem = *t % SECS_PER_DAY;
	rem += offset;
	while (rem < 0) {
		rem += SECS_PER_DAY;
		--days;
	}
	while (rem >= SECS_PER_DAY) {
		rem -= SECS_PER_DAY;
		++days;
	}
	tmbuf->tm_hour = rem / SECS_PER_HOUR;
	rem %= SECS_PER_HOUR;
	tmbuf->tm_min = rem / 60;
	tmbuf->tm_sec = rem % 60;
	/* January 1, 1970 was a Thursday.  */
	tmbuf->tm_wday = (4 + days) % 7;
	if (tmbuf->tm_wday < 0)
		tmbuf->tm_wday += 7;
	y = 1970;
	while (days >= (rem = __isleap(y) ? 366 : 365)) {
		++y;
		days -= rem;
	}
	while (days < 0) {
		--y;
		days += __isleap(y) ? 366 : 365;
	}
	tmbuf->tm_year = y - 1900;
	tmbuf->tm_yday = days;
	ip = __mon_lengths[__isleap(y)];
	for (y = 0; days >= ip[y]; ++y)
		days -= ip[y];
	tmbuf->tm_mon = y;
	tmbuf->tm_mday = days + 1;
	tmbuf->tm_isdst = -1;
}

#endif