/* Convert a `struct tm' to a time_t value. Copyright (C) 1993, 94, 95, 96, 97, 98, 99 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Paul Eggert (eggert@twinsun.com). The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. */ /* Define this to have a standalone program to test this implementation of mktime. */ #include /* Assume that leap seconds are not possible */ #undef LEAP_SECONDS_POSSIBLE #include /* Some systems define `time_t' here. */ #include #include #if 0 #ifndef CHAR_BIT # define CHAR_BIT 8 #endif /* The extra casts work around common compiler bugs. */ #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1)) /* The outer cast is needed to work around a bug in Cray C 5.0.3.0. It is necessary at least when t == time_t. */ #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \ ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0)) #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t))) #ifndef INT_MIN # define INT_MIN TYPE_MINIMUM (int) #endif #ifndef INT_MAX # define INT_MAX TYPE_MAXIMUM (int) #endif #ifndef TIME_T_MIN # define TIME_T_MIN TYPE_MINIMUM (time_t) #endif #ifndef TIME_T_MAX # define TIME_T_MAX TYPE_MAXIMUM (time_t) #endif #define TM_YEAR_BASE 1900 #define EPOCH_YEAR 1970 /* How many days come before each month (0-12). */ extern const unsigned short int __mon_yday[2][13]; /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP), measured in seconds, ignoring leap seconds. YEAR uses the same numbering as TM->tm_year. All values are in range, except possibly YEAR. If TP is null, return a nonzero value. If overflow occurs, yield the low order bits of the correct answer. */ static time_t __ydhms_tm_diff (int year, int yday, int hour, int min, int sec, const struct tm *tp) { if (!tp) return 1; else { /* Compute intervening leap days correctly even if year is negative. Take care to avoid int overflow. time_t overflow is OK, since only the low order bits of the correct time_t answer are needed. Don't convert to time_t until after all divisions are done, since time_t might be unsigned. */ int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3); int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3); int a100 = a4 / 25 - (a4 % 25 < 0); int b100 = b4 / 25 - (b4 % 25 < 0); int a400 = a100 >> 2; int b400 = b100 >> 2; int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); time_t years = year - (time_t) tp->tm_year; time_t days = (365 * years + intervening_leap_days + (yday - tp->tm_yday)); return (60 * (60 * (24 * days + (hour - tp->tm_hour)) + (min - tp->tm_min)) + (sec - tp->tm_sec)); } } /* 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; if (! (r = (*convert) (t, tp)) && *t) { time_t bad = *t; time_t ok = 0; struct tm tm; /* 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 = (bad < 0 ? bad + ((ok - bad) >> 1) : ok + ((bad - ok) >> 1)); if ((r = (*convert) (t, tp))) { tm = *r; ok = mid; } else bad = mid; } if (!r && ok) { /* The last conversion attempt failed; revert to the most recent successful attempt. */ *t = ok; *tp = tm; r = tp; } } return r; } /* Convert *TP to a time_t value, inverting the monotonic and mostly-unit-linear conversion function CONVERT. Use *OFFSET to keep track of a guess at the offset of the result, compared to what the result would be for UTC without leap seconds. If *OFFSET's guess is correct, only one CONVERT call is needed. */ time_t __mktime_internal (struct tm *tp, struct tm *(*convert) (const time_t *, struct tm *), time_t *offset) { time_t t, dt, t0, t1, t2; struct tm tm; /* The maximum number of probes (calls to CONVERT) should be enough to handle any combinations of time zone rule changes, solar time, leap seconds, and oscillations around a spring-forward gap. POSIX.1 prohibits leap seconds, but some hosts have them anyway. */ int remaining_probes = 6; /* Time requested. Copy it in case CONVERT modifies *TP; this can occur if TP is localtime's returned value and CONVERT is localtime. */ int sec = tp->tm_sec; int min = tp->tm_min; int hour = tp->tm_hour; int mday = tp->tm_mday; int mon = tp->tm_mon; int year_requested = tp->tm_year; int isdst = tp->tm_isdst; /* Ensure that mon is in range, and set year accordingly. */ int mon_remainder = mon % 12; int negative_mon_remainder = mon_remainder < 0; int mon_years = mon / 12 - negative_mon_remainder; int year = year_requested + mon_years; /* The other values need not be in range: the remaining code handles minor overflows correctly, assuming int and time_t arithmetic wraps around. Major overflows are caught at the end. */ /* Calculate day of year from year, month, and day of month. The result need not be in range. */ int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)] [mon_remainder + 12 * negative_mon_remainder]) + mday - 1); int sec_requested = sec; #if LEAP_SECONDS_POSSIBLE /* Handle out-of-range seconds specially, since __ydhms_tm_diff assumes every minute has 60 seconds. */ if (sec < 0) sec = 0; if (59 < sec) sec = 59; #endif /* Invert CONVERT by probing. First assume the same offset as last time. Then repeatedly use the error to improve the guess. */ tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE; tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0; t0 = __ydhms_tm_diff (year, yday, hour, min, sec, &tm); for (t = t1 = t2 = t0 + *offset; (dt = __ydhms_tm_diff (year, yday, hour, min, sec, __ranged_convert (convert, &t, &tm))); t1 = t2, t2 = t, t += dt) if (t == t1 && t != t2 && (isdst < 0 || tm.tm_isdst < 0 || (isdst != 0) != (tm.tm_isdst != 0))) /* We can't possibly find a match, as we are oscillating between two values. The requested time probably falls within a spring-forward gap of size DT. Follow the common practice in this case, which is to return a time that is DT away from the requested time, preferring a time whose tm_isdst differs from the requested value. In practice, this is more useful than returning -1. */ break; else if (--remaining_probes == 0) return -1; /* If we have a match, check whether tm.tm_isdst has the requested value, if any. */ if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst) { /* tm.tm_isdst has the wrong value. Look for a neighboring time with the right value, and use its UTC offset. Heuristic: probe the previous three calendar quarters (approximately), looking for the desired isdst. This isn't perfect, but it's good enough in practice. */ int quarter = 7889238; /* seconds per average 1/4 Gregorian year */ int i; /* If we're too close to the time_t limit, look in future quarters. */ if (t < TIME_T_MIN + 3 * quarter) quarter = -quarter; for (i = 1; i <= 3; i++) { time_t ot = t - i * quarter; struct tm otm; __ranged_convert (convert, &ot, &otm); if (otm.tm_isdst == isdst) { /* We found the desired tm_isdst. Extrapolate back to the desired time. */ t = ot + __ydhms_tm_diff (year, yday, hour, min, sec, &otm); __ranged_convert (convert, &t, &tm); break; } } } *offset = t - t0; #if LEAP_SECONDS_POSSIBLE if (sec_requested != tm.tm_sec) { /* Adjust time to reflect the tm_sec requested, not the normalized value. Also, repair any damage from a false match due to a leap second. */ t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60); if (! (*convert) (&t, &tm)) return -1; } #endif if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3) { /* time_t isn't large enough to rule out overflows in __ydhms_tm_diff, so check for major overflows. A gross check suffices, since if t has overflowed, it is off by a multiple of TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of the difference that is bounded by a small value. */ double dyear = (double) year_requested + mon_years - tm.tm_year; double dday = 366 * dyear + mday; double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested; /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce correct results, ie., it erroneously gives a positive value of 715827882. Setting a variable first then doing math on it seems to work. (ghazi@caip.rutgers.edu) */ const time_t time_t_max = TIME_T_MAX; const time_t time_t_min = TIME_T_MIN; if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec)) return -1; } *tp = tm; return t; } /* Convert *TP to a time_t value. */ time_t mktime (struct tm *tp) { static time_t localtime_offset; /* POSIX.1 8.1.1 requires that whenever mktime() is called, the time zone names contained in the external variable `tzname' shall be set as if the tzset() function had been called. */ tzset (); return __mktime_internal (tp, localtime_r, &localtime_offset); } #else /* Convert *TP to a time_t value. */ time_t mktime (struct tm *tp) { time_t m_secs=tp->tm_min*60; time_t h_secs=tp->tm_hour*3600; time_t d_secs=tp->tm_yday*86400; time_t y_secs=(tp->tm_year-70)*31536000; time_t l_secs1=((tp->tm_year-69)/4)*86400; time_t l_secs2=((tp->tm_year-1)/100)*86400; time_t l_secs3=((tp->tm_year+299)/400)*86400; return m_secs+h_secs+d_secs+y_secs+l_secs1-l_secs2+l_secs3+tp->tm_gmtoff; } #endif