+ verify (int_no_wider_than_time_t, INT_MAX <= TIME_T_MAX);
+ if (WRAPV)
+ {
+ time_t sum = a + b;
+ return (sum < a) == (b < 0);
+ }
+ else
+ {
+ int a_odd = a & 1;
+ time_t avg = SHR (a, 1) + (SHR (b, 1) + (a_odd & b));
+ return TIME_T_MIN / 2 <= avg && avg <= TIME_T_MAX / 2;
+ }
+}
+
+/* Return a time_t value corresponding to (YEAR-YDAY HOUR:MIN:SEC),
+ assuming that *T corresponds to *TP and that no clock adjustments
+ occurred between *TP and the desired time.
+ If TP is null, return a value not equal to *T; this avoids false matches.
+ If overflow occurs, yield the minimal or maximal value, except do not
+ yield a value equal to *T. */
+static time_t
+guess_time_tm (long_int year, long_int yday, int hour, int min, int sec,
+ const time_t *t, const struct tm *tp)
+{
+ if (tp)
+ {
+ time_t d = ydhms_diff (year, yday, hour, min, sec,
+ tp->tm_year, tp->tm_yday,
+ tp->tm_hour, tp->tm_min, tp->tm_sec);
+ if (time_t_add_ok (*t, d))
+ return *t + d;
+ }
+
+ /* Overflow occurred one way or another. Return the nearest result
+ that is actually in range, except don't report a zero difference
+ if the actual difference is nonzero, as that would cause a false
+ match; and don't oscillate between two values, as that would
+ confuse the spring-forward gap detector. */
+ return (*t < TIME_T_MIDPOINT
+ ? (*t <= TIME_T_MIN + 1 ? *t + 1 : TIME_T_MIN)
+ : (TIME_T_MAX - 1 <= *t ? *t - 1 : TIME_T_MAX));
+}
+
+/* Use CONVERT to convert *T to a broken down time in *TP.
+ If *T is out of range for conversion, adjust it so that
+ it is the nearest in-range value and then convert that. */
+static struct tm *
+ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
+ time_t *t, struct tm *tp)
+{
+ struct tm *r = convert (t, tp);
+
+ if (!r && *t)
+ {
+ time_t bad = *t;
+ time_t ok = 0;
+
+ /* BAD is a known unconvertible time_t, and OK is a known good one.
+ Use binary search to narrow the range between BAD and OK until
+ they differ by 1. */
+ while (bad != ok + (bad < 0 ? -1 : 1))
+ {
+ time_t mid = *t = time_t_avg (ok, bad);
+ r = convert (t, tp);
+ if (r)
+ ok = mid;
+ else
+ bad = mid;
+ }
+
+ if (!r && ok)
+ {
+ /* The last conversion attempt failed;
+ revert to the most recent successful attempt. */
+ *t = ok;
+ r = convert (t, tp);
+ }
+ }