dg@lakart.UUCP (David Goodenough) (02/13/89)
I recently posted a DST check program / subroutine, based on a quote
that stated that "DST starts the last Sunday in April, and ends the
last Sunday in October". I have been informed that Congress changed
the rules in 1987, and that is no longer valid. DST _NOW_ begins
the first Sunday in April. Hence I provide a revised isdst()
subroutine to respect this.
My apologies for misleading everyone on the basis of out of date
information. (-: I will hit myself over the head with a sock full of
cold custard, 27 times as pennance. :-)
--
dg@lakart.UUCP - David Goodenough +---+
IHS | +-+-+
....... !harvard!xait!lakart!dg +-+-+ |
AKA: dg%lakart.uucp@xait.xerox.com +---+
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main(n, a)
char **a;
{
int i, j;
j = atoi(a[1]);
for (i = 1; i <= 10; i++)
printf("%d %d %d %d: %d\n", i, 4, j, 19, isdst(i, 4, j, 19));
putchar('\n');
for (i = 21; i <= 31; i++)
printf("%d %d %d %d: %d\n", i, 10, j, 19, isdst(i, 10, j, 19));
}
/*
* isdst(day, month, year, century)
* feed in numbers as you'd expect: today (2-12-1989) would be
* isdst(12, 2, 89, 19)
*/
isdst(d, m, y, c)
{
if (m > 4 && m < 10)
return(1); /* May thru Sept are always dst */
if (m == 10)
{ /* Oct - see if there's a Sunday after given day */
while (++d <= 31)
if (dayofweek(d, m, y, c) == 0)
return(1); /* yes, so it is dst */
}
else if (m == 4)
{ /* April - see if there's a Sunday beforegiven day */
while (d >= 1)
if (dayofweek(d--, m, y, c) == 0)
return(1); /* yes, so this is also dst */
}
return(0); /* either Jan - Mar, Nov, Dec, or no good in Apr
* or Oct */
}
dayofweek(d, m, y, c)
{
if ((m = m - 2) < 1)
{
m = m + 12;
if (y-- == 0)
{
y = 99;
c--;
}
}
return(((13 * m - 1) / 5 + d + y + y / 4 + c / 4 - 2 * c) % 7);
/* don't ask. Just trust me: it does work */
}