normalize time for strftime() (without the isdst effects of

mktime()) using a custom mini_mktime()
	Message-Id: <199909232154.RAA25151@leggy.zk3.dec.com>
	Subject: Re: [ID 19990913.003] Possible bug using POSIX::strftime Digital UNIX Perl 5.005_03

p4raw-id: //depot/perl@4223

3 files changed, 195 insertions, 8 deletions

diff --git a/ext/POSIX/POSIX.pod b/ext/POSIX/POSIX.pod
index 75d4d1d2a6..08300e4337 100644
--- a/ext/POSIX/POSIX.pod
+++ b/ext/POSIX/POSIX.pod
@@ -1023,8 +1023,9 @@ about these and the other arguments.
 If you want your code to be portable, your format (C<fmt>) argument
 should use only the conversion specifiers defined by the ANSI C
 standard.  These are C<aAbBcdHIjmMpSUwWxXyYZ%>.
-On platforms that need it, the given arguments are made consistent
-by calling C<mktime()> before calling your system's C<strftime()> function.
+The given arguments are made consistent
+as though by calling C<mktime()> before calling your system's
+C<strftime()> function, except that the C<isdst> value is not affected.
 
 The string for Tuesday, December 12, 1995.
 
diff --git a/ext/POSIX/POSIX.xs b/ext/POSIX/POSIX.xs
index e828d52e5e..23c38b5e20 100644
--- a/ext/POSIX/POSIX.xs
+++ b/ext/POSIX/POSIX.xs
@@ -332,6 +332,196 @@ init_tm(struct tm *ptm)		/* see mktime, strftime and asctime	*/
 # define init_tm(ptm)
 #endif
 
+/*
+ * mini_mktime - normalise struct tm values without the localtime()
+ * semantics (and overhead) of mktime().
+ */
+static void
+mini_mktime(struct tm *ptm)
+{
+    int yearday;
+    int secs;
+    int month, mday, year, jday;
+    int odd_cent, odd_year;
+
+#define	DAYS_PER_YEAR	365
+#define	DAYS_PER_QYEAR	(4*DAYS_PER_YEAR+1)
+#define	DAYS_PER_CENT	(25*DAYS_PER_QYEAR-1)
+#define	DAYS_PER_QCENT	(4*DAYS_PER_CENT+1)
+#define	SECS_PER_HOUR	(60*60)
+#define	SECS_PER_DAY	(24*SECS_PER_HOUR)
+/* parentheses deliberately absent on these two, otherwise they don't work */
+#define	MONTH_TO_DAYS	153/5
+#define	DAYS_TO_MONTH	5/153
+/* offset to bias by March (month 4) 1st between month/mday & year finding */
+#define	YEAR_ADJUST	(4*MONTH_TO_DAYS+1)
+/* as used here, the algorithm leaves Sunday as day 1 unless we adjust it */
+#define	WEEKDAY_BIAS	6	/* (1+6)%7 makes Sunday 0 again */
+
+/*
+ * Year/day algorithm notes:
+ *
+ * With a suitable offset for numeric value of the month, one can find
+ * an offset into the year by considering months to have 30.6 (153/5) days,
+ * using integer arithmetic (i.e., with truncation).  To avoid too much
+ * messing about with leap days, we consider January and February to be
+ * the 13th and 14th month of the previous year.  After that transformation,
+ * we need the month index we use to be high by 1 from 'normal human' usage,
+ * so the month index values we use run from 4 through 15.
+ *
+ * Given that, and the rules for the Gregorian calendar (leap years are those
+ * divisible by 4 unless also divisible by 100, when they must be divisible
+ * by 400 instead), we can simply calculate the number of days since some
+ * arbitrary 'beginning of time' by futzing with the (adjusted) year number,
+ * the days we derive from our month index, and adding in the day of the
+ * month.  The value used here is not adjusted for the actual origin which
+ * it normally would use (1 January A.D. 1), since we're not exposing it.
+ * We're only building the value so we can turn around and get the
+ * normalised values for the year, month, day-of-month, and day-of-year.
+ *
+ * For going backward, we need to bias the value we're using so that we find
+ * the right year value.  (Basically, we don't want the contribution of
+ * March 1st to the number to apply while deriving the year).  Having done
+ * that, we 'count up' the contribution to the year number by accounting for
+ * full quadracenturies (400-year periods) with their extra leap days, plus
+ * the contribution from full centuries (to avoid counting in the lost leap
+ * days), plus the contribution from full quad-years (to count in the normal
+ * leap days), plus the leftover contribution from any non-leap years.
+ * At this point, if we were working with an actual leap day, we'll have 0
+ * days left over.  This is also true for March 1st, however.  So, we have
+ * to special-case that result, and (earlier) keep track of the 'odd'
+ * century and year contributions.  If we got 4 extra centuries in a qcent,
+ * or 4 extra years in a qyear, then it's a leap day and we call it 29 Feb.
+ * Otherwise, we add back in the earlier bias we removed (the 123 from
+ * figuring in March 1st), find the month index (integer division by 30.6),
+ * and the remainder is the day-of-month.  We then have to convert back to
+ * 'real' months (including fixing January and February from being 14/15 in
+ * the previous year to being in the proper year).  After that, to get
+ * tm_yday, we work with the normalised year and get a new yearday value for
+ * January 1st, which we subtract from the yearday value we had earlier,
+ * representing the date we've re-built.  This is done from January 1
+ * because tm_yday is 0-origin.
+ *
+ * Since POSIX time routines are only guaranteed to work for times since the
+ * UNIX epoch (00:00:00 1 Jan 1970 UTC), the fact that this algorithm
+ * applies Gregorian calendar rules even to dates before the 16th century
+ * doesn't bother me.  Besides, you'd need cultural context for a given
+ * date to know whether it was Julian or Gregorian calendar, and that's
+ * outside the scope for this routine.  Since we convert back based on the
+ * same rules we used to build the yearday, you'll only get strange results
+ * for input which needed normalising, or for the 'odd' century years which
+ * were leap years in the Julian calander but not in the Gregorian one.
+ * I can live with that.
+ *
+ * This algorithm also fails to handle years before A.D. 1 gracefully, but
+ * that's still outside the scope for POSIX time manipulation, so I don't
+ * care.
+ */
+
+    year = 1900 + ptm->tm_year;
+    month = ptm->tm_mon;
+    mday = ptm->tm_mday;
+    /* allow given yday with no month & mday to dominate the result */
+    if (ptm->tm_yday >= 0 && mday <= 0 && month <= 0) {
+	month = 0;
+	mday = 0;
+	jday = 1 + ptm->tm_yday;
+    }
+    else {
+	jday = 0;
+    }
+    if (month >= 2)
+	month+=2;
+    else
+	month+=14, year--;
+    yearday = DAYS_PER_YEAR * year + year/4 - year/100 + year/400;
+    yearday += month*MONTH_TO_DAYS + mday + jday;
+    /*
+     * Note that we don't know when leap-seconds were or will be,
+     * so we have to trust the user if we get something which looks
+     * like a sensible leap-second.  Wild values for seconds will
+     * be rationalised, however.
+     */
+    if ((unsigned) ptm->tm_sec <= 60) {
+	secs = 0;
+    }
+    else {
+	secs = ptm->tm_sec;
+	ptm->tm_sec = 0;
+    }
+    secs += 60 * ptm->tm_min;
+    secs += SECS_PER_HOUR * ptm->tm_hour;
+    if (secs < 0) {
+	if (secs-(secs/SECS_PER_DAY*SECS_PER_DAY) < 0) {
+	    /* got negative remainder, but need positive time */
+	    /* back off an extra day to compensate */
+	    yearday += (secs/SECS_PER_DAY)-1;
+	    secs -= SECS_PER_DAY * (secs/SECS_PER_DAY - 1);
+	}
+	else {
+	    yearday += (secs/SECS_PER_DAY);
+	    secs -= SECS_PER_DAY * (secs/SECS_PER_DAY);
+	}
+    }
+    else if (secs >= SECS_PER_DAY) {
+	yearday += (secs/SECS_PER_DAY);
+	secs %= SECS_PER_DAY;
+    }
+    ptm->tm_hour = secs/SECS_PER_HOUR;
+    secs %= SECS_PER_HOUR;
+    ptm->tm_min = secs/60;
+    secs %= 60;
+    ptm->tm_sec += secs;
+    /* done with time of day effects */
+    /*
+     * The algorithm for yearday has (so far) left it high by 428.
+     * To avoid mistaking a legitimate Feb 29 as Mar 1, we need to
+     * bias it by 123 while trying to figure out what year it
+     * really represents.  Even with this tweak, the reverse
+     * translation fails for years before A.D. 0001.
+     * It would still fail for Feb 29, but we catch that one below.
+     */
+    jday = yearday;	/* save for later fixup vis-a-vis Jan 1 */
+    yearday -= YEAR_ADJUST;
+    year = (yearday / DAYS_PER_QCENT) * 400;
+    yearday %= DAYS_PER_QCENT;
+    odd_cent = yearday / DAYS_PER_CENT;
+    year += odd_cent * 100;
+    yearday %= DAYS_PER_CENT;
+    year += (yearday / DAYS_PER_QYEAR) * 4;
+    yearday %= DAYS_PER_QYEAR;
+    odd_year = yearday / DAYS_PER_YEAR;
+    year += odd_year;
+    yearday %= DAYS_PER_YEAR;
+    if (!yearday && (odd_cent==4 || odd_year==4)) { /* catch Feb 29 */
+	month = 1;
+	yearday = 29;
+    }
+    else {
+	yearday += YEAR_ADJUST;	/* recover March 1st crock */
+	month = yearday*DAYS_TO_MONTH;
+	yearday -= month*MONTH_TO_DAYS;
+	/* recover other leap-year adjustment */
+	if (month > 13) {
+	    month-=14;
+	    year++;
+	}
+	else {
+	    month-=2;
+	}
+    }
+    ptm->tm_year = year - 1900;
+    ptm->tm_mon = month;
+    ptm->tm_mday = yearday;
+    /* re-build yearday based on Jan 1 to get tm_yday */
+    year--;
+    yearday = year*DAYS_PER_YEAR + year/4 - year/100 + year/400;
+    yearday += 14*MONTH_TO_DAYS + 1;
+    ptm->tm_yday = jday - yearday;
+    /* fix tm_wday if not overridden by caller */
+    if ((unsigned)ptm->tm_wday > 6)
+	ptm->tm_wday = (jday + WEEKDAY_BIAS) % 7;
+}
 
 #ifdef HAS_LONG_DOUBLE
 #  if LONG_DOUBLESIZE > DOUBLESIZE
@@ -3652,9 +3842,7 @@ strftime(fmt, sec, min, hour, mday, mon, year, wday = -1, yday = -1, isdst = -1)
 	    mytm.tm_wday = wday;
 	    mytm.tm_yday = yday;
 	    mytm.tm_isdst = isdst;
-#if defined(HINT_STRFTIME_NEEDS_MKTIME)
-	    (void) mktime(&mytm);
-#endif
+	    mini_mktime(&mytm);
 	    len = strftime(tmpbuf, sizeof tmpbuf, fmt, &mytm);
 	    /*
 	    ** The following is needed to handle to the situation where 
diff --git a/ext/POSIX/hints/linux.pl b/ext/POSIX/hints/linux.pl
index 8cec446044..f1d19814ae 100644
--- a/ext/POSIX/hints/linux.pl
+++ b/ext/POSIX/hints/linux.pl
@@ -2,6 +2,4 @@
 # Thanks to Bart Schuller <schuller@Lunatech.com>
 # See Message-ID: <19971009002636.50729@tanglefoot>
 #  XXX A Configure test is needed.
-$self->{CCFLAGS} = $Config{ccflags}
-		 . ' -DHINT_STRFTIME_NEEDS_MKTIME'
-		 . ' -DSTRUCT_TM_HASZONE -DHINT_SC_EXIST' ;
+$self->{CCFLAGS} = $Config{ccflags} . ' -DSTRUCT_TM_HASZONE -DHINT_SC_EXIST' ;