diff options
Diffstat (limited to 'time/mktime.c')
| -rw-r--r-- | time/mktime.c | 197 |
1 files changed, 99 insertions, 98 deletions
diff --git a/time/mktime.c b/time/mktime.c index 6d5b8cf..dc83985 100644 --- a/time/mktime.c +++ b/time/mktime.c @@ -250,45 +250,25 @@ long_int_avg (long_int a, long_int b) return shr (a, 1) + shr (b, 1) + ((a | b) & 1); } -/* 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. - Although T and the returned value are of type long_int, - they represent time_t values and must be in time_t range. - If TP is null, return a value not equal to T; this avoids false matches. +/* Return a long_int value corresponding to (YEAR-YDAY HOUR:MIN:SEC) + minus *TP seconds, assuming no clock adjustments occurred between + the two timestamps. + YEAR and YDAY must not be so large that multiplying them by three times the number of seconds in a year (or day, respectively) would overflow long_int. - If TP is non-null and the returned value would be out of range, set - errno to EOVERFLOW and yield a minimal or maximal in-range value - that is not equal to T. */ + *TP should be in the usual range. */ static long_int -guess_time_tm (long_int year, long_int yday, int hour, int min, int sec, - long_int t, const struct tm *tp) +tm_diff (long_int year, long_int yday, int hour, int min, int sec, + struct tm const *tp) { - if (tp) - { - long_int result; - long_int d = ydhms_diff (year, yday, hour, min, sec, - tp->tm_year, tp->tm_yday, - tp->tm_hour, tp->tm_min, tp->tm_sec); - if (! INT_ADD_WRAPV (t, d, &result)) - return result; - __set_errno (EOVERFLOW); - } - - /* An error occurred, probably overflow. 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 < long_int_avg (mktime_min, mktime_max) - ? (t <= mktime_min + 1 ? t + 1 : mktime_min) - : (mktime_max - 1 <= t ? t - 1 : mktime_max)); + return ydhms_diff (year, yday, hour, min, sec, + tp->tm_year, tp->tm_yday, + tp->tm_hour, tp->tm_min, tp->tm_sec); } /* Use CONVERT to convert T to a struct tm value in *TM. T must be in - range for time_t. Return TM if successful, NULL if T is out of - range for CONVERT. */ + range for time_t. Return TM if successful, NULL (setting errno) on + failure. */ static struct tm * convert_time (struct tm *(*convert) (const time_t *, struct tm *), long_int t, struct tm *tm) @@ -300,49 +280,48 @@ convert_time (struct tm *(*convert) (const time_t *, struct tm *), /* 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. - A value is in range if it fits in both time_t and long_int. */ + A value is in range if it fits in both time_t and long_int. + Return TP on success, NULL (setting errno) on failure. */ static struct tm * ranged_convert (struct tm *(*convert) (const time_t *, struct tm *), long_int *t, struct tm *tp) { - struct tm *r; - if (*t < mktime_min) - *t = mktime_min; - else if (mktime_max < *t) - *t = mktime_max; - r = convert_time (convert, *t, tp); - - if (!r && *t) + long_int t1 = (*t < mktime_min ? mktime_min + : *t <= mktime_max ? *t : mktime_max); + struct tm *r = convert_time (convert, t1, tp); + if (r) { - long_int bad = *t; - long_int ok = 0; - - /* BAD is a known unconvertible value, and OK is a known good one. - Use binary search to narrow the range between BAD and OK until - they differ by 1. */ - while (true) - { - long_int mid = long_int_avg (ok, bad); - if (mid == ok || mid == bad) - break; - r = convert_time (convert, mid, tp); - if (r) - ok = mid; - else - bad = mid; - } + *t = t1; + return r; + } + if (errno != EOVERFLOW) + return NULL; - *t = ok; + long_int bad = t1; + long_int ok = 0; + struct tm oktm; oktm.tm_sec = -1; - if (!r && ok) - { - /* The last conversion attempt failed; - revert to the most recent successful attempt. */ - r = convert_time (convert, ok, tp); - } + /* BAD is a known out-of-range value, and OK is a known in-range one. + Use binary search to narrow the range between BAD and OK until + they differ by 1. */ + while (true) + { + long_int mid = long_int_avg (ok, bad); + if (mid == ok || mid == bad) + break; + if (convert_time (convert, mid, tp)) + ok = mid, oktm = *tp; + else if (errno != EOVERFLOW) + return NULL; + else + bad = mid; } - return r; + if (oktm.tm_sec < 0) + return NULL; + *t = ok; + *tp = oktm; + return tp; } @@ -359,7 +338,6 @@ __mktime_internal (struct tm *tp, struct tm *(*convert) (const time_t *, struct tm *), mktime_offset_t *offset) { - long_int t, gt, t0, t1, t2; struct tm tm; /* The maximum number of probes (calls to CONVERT) should be enough @@ -379,7 +357,7 @@ __mktime_internal (struct tm *tp, int isdst = tp->tm_isdst; /* 1 if the previous probe was DST. */ - int dst2; + int dst2 = 0; /* Ensure that mon is in range, and set year accordingly. */ int mon_remainder = mon % 12; @@ -418,36 +396,46 @@ __mktime_internal (struct tm *tp, time. */ INT_SUBTRACT_WRAPV (0, off, &negative_offset_guess); - t0 = ydhms_diff (year, yday, hour, min, sec, - EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, negative_offset_guess); + long_int t0 = ydhms_diff (year, yday, hour, min, sec, + EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, + negative_offset_guess); + long_int t = t0, t1 = t0, t2 = t0; /* Repeatedly use the error to improve the guess. */ - for (t = t1 = t2 = t0, dst2 = 0; - (gt = guess_time_tm (year, yday, hour, min, sec, t, - ranged_convert (convert, &t, &tm)), - t != gt); - t1 = t2, t2 = t, t = gt, dst2 = tm.tm_isdst != 0) - if (t == t1 && t != t2 - && (tm.tm_isdst < 0 - || (isdst < 0 - ? dst2 <= (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 GT - T. Follow the common - practice in this case, which is to return a time that is GT - T - away from the requested time, preferring a time whose - tm_isdst differs from the requested value. (If no tm_isdst - was requested and only one of the two values has a nonzero - tm_isdst, prefer that value.) In practice, this is more - useful than returning -1. */ - goto offset_found; - else if (--remaining_probes == 0) - { - __set_errno (EOVERFLOW); + while (true) + { + if (! ranged_convert (convert, &t, &tm)) return -1; - } + long_int dt = tm_diff (year, yday, hour, min, sec, &tm); + if (dt == 0) + break; + + if (t == t1 && t != t2 + && (tm.tm_isdst < 0 + || (isdst < 0 + ? dst2 <= (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. (If no tm_isdst + was requested and only one of the two values has a nonzero + tm_isdst, prefer that value.) In practice, this is more + useful than returning -1. */ + goto offset_found; + + remaining_probes--; + if (remaining_probes == 0) + { + __set_errno (EOVERFLOW); + return -1; + } + + t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0; + } /* We have a match. Check whether tm.tm_isdst has the requested value, if any. */ @@ -489,17 +477,30 @@ __mktime_internal (struct tm *tp, if (! INT_ADD_WRAPV (t, delta * direction, &ot)) { struct tm otm; - ranged_convert (convert, &ot, &otm); + if (! ranged_convert (convert, &ot, &otm)) + return -1; if (! isdst_differ (isdst, otm.tm_isdst)) { /* We found the desired tm_isdst. Extrapolate back to the desired time. */ - t = guess_time_tm (year, yday, hour, min, sec, ot, &otm); - ranged_convert (convert, &t, &tm); - goto offset_found; + long_int gt = ot + tm_diff (year, yday, hour, min, sec, + &otm); + if (mktime_min <= gt && gt <= mktime_max) + { + if (convert_time (convert, gt, &tm)) + { + t = gt; + goto offset_found; + } + if (errno != EOVERFLOW) + return -1; + } } } } + + __set_errno (EOVERFLOW); + return -1; } offset_found: |