Message ID | 20180418201819.15952-11-albert.aribaud@3adev.fr |
---|---|

State | New, archived |

Headers | show |

On Wed, 18 Apr 2018, Albert ARIBAUD (3ADEV) wrote: > __mktime64 is designed similar to mktime, including checks on (64-bit) > integer limits, and respects the same Posix requirements as __mktime does, > i.e. calls tzset(). As per comments on previous versions of these patches, such duplication of large, complicated pieces of code must be avoided; you want a main function that uses the 64-bit types and the 32-bit function should be a simple wrapper around it.

diff --git a/include/time.h b/include/time.h index b0a1199308..d74f66e7c6 100644 --- a/include/time.h +++ b/include/time.h @@ -61,6 +61,15 @@ extern time_t __mktime_internal (struct tm *__tp, struct tm *(*__func) (const time_t *, struct tm *), time_t *__offset) attribute_hidden; + +/* Subroutine of `__mktime64'. Return the `__time64_t' representation of TP and + normalize TP, given that a `struct tm *' maps to a `__time64_t' as performed + by FUNC. Keep track of next guess for __time64_t offset in *OFFSET. */ +extern __time64_t __mktime64_internal (struct tm *__tp, + struct tm *(*__func) (const __time64_t *, + struct tm *), + __time64_t *__offset) attribute_hidden; + extern struct tm *__localtime_r (const time_t *__timer, struct tm *__tp) attribute_hidden; diff --git a/time/Versions b/time/Versions index 0ad2749f2c..f5ccacc759 100644 --- a/time/Versions +++ b/time/Versions @@ -70,5 +70,6 @@ libc { __ctime64; __ctime64_r; __gmtime64; __gmtime64_r; __localtime64; __localtime64_r; + __mktime64; __timelocal64_r; } } diff --git a/time/mktime.c b/time/mktime.c index 5f038a212f..d85a2a3704 100644 --- a/time/mktime.c +++ b/time/mktime.c @@ -599,6 +599,409 @@ weak_alias (mktime, timelocal) libc_hidden_def (mktime) libc_hidden_weak (timelocal) #endif + +/* Return an integer value measuring (YEAR1-YDAY1 HOUR1:MIN1:SEC1) - + (YEAR0-YDAY0 HOUR0:MIN0:SEC0) in seconds, assuming that the clocks + were not adjusted between the time stamps. + + The YEAR values uses the same numbering as TP->tm_year. Values + need not be in the usual range. However, YEAR1 must not be less + than 2 * INT_MIN or greater than 2 * INT_MAX. + + The result may overflow. It is the caller's responsibility to + detect overflow. */ + +static __time64_t +ydhms64_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1, + int year0, int yday0, int hour0, int min0, int sec0) +{ + verify (C99_integer_division, -1 / 2 == 0); + + /* Compute intervening leap days correctly even if year is negative. + Take care to avoid integer overflow here. */ + int a4 = SHR (year1, 2) + SHR (TM_YEAR_BASE, 2) - ! (year1 & 3); + int b4 = SHR (year0, 2) + SHR (TM_YEAR_BASE, 2) - ! (year0 & 3); + int a100 = a4 / 25 - (a4 % 25 < 0); + int b100 = b4 / 25 - (b4 % 25 < 0); + int a400 = SHR (a100, 2); + int b400 = SHR (b100, 2); + int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); + + /* Compute the desired time in __time64_t precision. Overflow might + occur here. */ + __time64_t tyear1 = year1; + __time64_t years = tyear1 - year0; + __time64_t days = 365 * years + yday1 - yday0 + intervening_leap_days; + __time64_t hours = 24 * days + hour1 - hour0; + __time64_t minutes = 60 * hours + min1 - min0; + __time64_t seconds = 60 * minutes + sec1 - sec0; + return seconds; +} + +/* Return the average of A and B, even if A + B would overflow. */ +static __time64_t +time64_t_avg (__time64_t a, __time64_t b) +{ + return SHR (a, 1) + SHR (b, 1) + (a & b & 1); +} + +/* Return 1 if A + B does not overflow. If __time64_t is unsigned and if + B's top bit is set, assume that the sum represents A - -B, and + return 1 if the subtraction does not wrap around. */ +static int +time64_t_add_ok (__time64_t a, __time64_t b) +{ + if (! TYPE_SIGNED (__time64_t)) + { + __time64_t sum = a + b; + return (sum < a) == (TIME_T_MIDPOINT <= b); + } + else if (WRAPV) + { + __time64_t sum = a + b; + return (sum < a) == (b < 0); + } + else + { + __time64_t avg = time64_t_avg (a, b); + return TIME_T_MIN / 2 <= avg && avg <= TIME_T_MAX / 2; + } +} + +/* Return 1 if A + B does not overflow. */ +static int +time64_t_int_add_ok (__time64_t a, int b) +{ + verify (int_no_wider_than_time64_t, INT_MAX <= TIME_T_MAX); + if (WRAPV) + { + __time64_t sum = a + b; + return (sum < a) == (b < 0); + } + else + { + int a_odd = a & 1; + __time64_t avg = SHR (a, 1) + (SHR (b, 1) + (a_odd & b)); + return TIME_T_MIN / 2 <= avg && avg <= TIME_T_MAX / 2; + } +} + +/* Return a __time64_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 __time64_t +guess_time64_tm (long_int year, long_int yday, int hour, int min, int sec, + const __time64_t *t, const struct tm *tp) +{ + if (tp) + { + __time64_t d = ydhms64_diff (year, yday, hour, min, sec, + tp->tm_year, tp->tm_yday, + tp->tm_hour, tp->tm_min, tp->tm_sec); + if (time64_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 * +ranged64_convert (struct tm *(*convert) (const __time64_t *, struct tm *), + __time64_t *t, struct tm *tp) +{ + struct tm *r = convert (t, tp); + + if (!r && *t) + { + __time64_t bad = *t; + __time64_t ok = 0; + + /* BAD is a known unconvertible __time64_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)) + { + __time64_t mid = *t = time64_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); + } + } + + return r; +} + + +/* Convert *TP to a __time64_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. + This function is external because it is used also by timegm.c. */ +__time64_t +__mktime64_internal (struct tm *tp, + struct tm *(*convert) (const __time64_t *, struct tm *), + __time64_t *offset) +{ + __time64_t t, gt, 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; + + /* 1 if the previous probe was DST. */ + int dst2; + + /* 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; + long_int lyear_requested = year_requested; + long_int year = lyear_requested + mon_years; + + /* The other values need not be in range: + the remaining code handles minor overflows correctly, + assuming int and __time64_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 mon_yday = ((__mon_yday[leapyear (year)] + [mon_remainder + 12 * negative_mon_remainder]) + - 1); + long_int lmday = mday; + long_int yday = mon_yday + lmday; + + __time64_t guessed_offset = *offset; + + 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; + } + + /* Invert CONVERT by probing. First assume the same offset as last + time. */ + + t0 = ydhms64_diff (year, yday, hour, min, sec, + EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, - guessed_offset); + + if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3) + { + /* __time64_t isn't large enough to rule out overflows, so check + for major overflows. A gross check suffices, since if t0 + 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. */ + + /* Approximate log base 2 of the number of time units per + biennium. A biennium is 2 years; use this unit instead of + years to avoid integer overflow. For example, 2 average + Gregorian years are 2 * 365.2425 * 24 * 60 * 60 seconds, + which is 63113904 seconds, and rint (log2 (63113904)) is + 26. */ + int ALOG2_SECONDS_PER_BIENNIUM = 26; + int ALOG2_MINUTES_PER_BIENNIUM = 20; + int ALOG2_HOURS_PER_BIENNIUM = 14; + int ALOG2_DAYS_PER_BIENNIUM = 10; + int LOG2_YEARS_PER_BIENNIUM = 1; + + int approx_requested_biennia = + (SHR (year_requested, LOG2_YEARS_PER_BIENNIUM) + - SHR (EPOCH_YEAR - TM_YEAR_BASE, LOG2_YEARS_PER_BIENNIUM) + + SHR (mday, ALOG2_DAYS_PER_BIENNIUM) + + SHR (hour, ALOG2_HOURS_PER_BIENNIUM) + + SHR (min, ALOG2_MINUTES_PER_BIENNIUM) + + (LEAP_SECONDS_POSSIBLE + ? 0 + : SHR (sec, ALOG2_SECONDS_PER_BIENNIUM))); + + int approx_biennia = SHR (t0, ALOG2_SECONDS_PER_BIENNIUM); + int diff = approx_biennia - approx_requested_biennia; + int approx_abs_diff = diff < 0 ? -1 - diff : diff; + + /* IRIX 4.0.5 cc miscalculates TIME_T_MIN / 3: it erroneously + gives a positive value of 715827882. Setting a variable + first then doing math on it seems to work. + (ghazi@caip.rutgers.edu) */ + __time64_t time64_t_max = TIME_T_MAX; + __time64_t time64_t_min = TIME_T_MIN; + __time64_t overflow_threshold = + (time64_t_max / 3 - time64_t_min / 3) >> ALOG2_SECONDS_PER_BIENNIUM; + + if (overflow_threshold < approx_abs_diff) + { + /* Overflow occurred. Try repairing it; this might work if + the time zone offset is enough to undo the overflow. */ + __time64_t repaired_t0 = -1 - t0; + approx_biennia = SHR (repaired_t0, ALOG2_SECONDS_PER_BIENNIUM); + diff = approx_biennia - approx_requested_biennia; + approx_abs_diff = diff < 0 ? -1 - diff : diff; + if (overflow_threshold < approx_abs_diff) + return -1; + guessed_offset += repaired_t0 - t0; + t0 = repaired_t0; + } + } + + /* Repeatedly use the error to improve the guess. */ + + for (t = t1 = t2 = t0, dst2 = 0; + (gt = guess_time64_tm (year, yday, hour, min, sec, &t, + ranged64_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) + return -1; + + /* We have a match. Check whether tm.tm_isdst has the requested + value, if any. */ + if (isdst_differ (isdst, 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 adjacent timestamps in both directions, + looking for the desired isdst. This should work for all real + time zone histories in the tz database. */ + + /* Distance between probes when looking for a DST boundary. In + tzdata2003a, the shortest period of DST is 601200 seconds + (e.g., America/Recife starting 2000-10-08 01:00), and the + shortest period of non-DST surrounded by DST is 694800 + seconds (Africa/Tunis starting 1943-04-17 01:00). Use the + minimum of these two values, so we don't miss these short + periods when probing. */ + int stride = 601200; + + /* The longest period of DST in tzdata2003a is 536454000 seconds + (e.g., America/Jujuy starting 1946-10-01 01:00). The longest + period of non-DST is much longer, but it makes no real sense + to search for more than a year of non-DST, so use the DST + max. */ + int duration_max = 536454000; + + /* Search in both directions, so the maximum distance is half + the duration; add the stride to avoid off-by-1 problems. */ + int delta_bound = duration_max / 2 + stride; + + int delta, direction; + + for (delta = stride; delta < delta_bound; delta += stride) + for (direction = -1; direction <= 1; direction += 2) + if (time64_t_int_add_ok (t, delta * direction)) + { + __time64_t ot = t + delta * direction; + struct tm otm; + ranged64_convert (convert, &ot, &otm); + if (! isdst_differ (isdst, otm.tm_isdst)) + { + /* We found the desired tm_isdst. + Extrapolate back to the desired time. */ + t = guess_time64_tm (year, yday, hour, min, sec, &ot, &otm); + ranged64_convert (convert, &t, &tm); + goto offset_found; + } + } + } + + offset_found: + *offset = guessed_offset + t - t0; + + if (LEAP_SECONDS_POSSIBLE && 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. */ + int sec_adjustment = (sec == 0 && tm.tm_sec == 60) - sec; + if (! time64_t_int_add_ok (t, sec_requested)) + return -1; + t1 = t + sec_requested; + if (! time64_t_int_add_ok (t1, sec_adjustment)) + return -1; + t2 = t1 + sec_adjustment; + if (! convert (&t2, &tm)) + return -1; + t = t2; + } + + *tp = tm; + return t; +} + + +/* This uses a signed type wide enough to hold any UTC offset in seconds. */ +static __time64_t localtime64_offset; + +/* Convert *TP to a __time64_t value. */ +__time64_t +__mktime64 (struct tm *tp) +{ +#ifdef _LIBC + /* 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 (); +#endif + + return __mktime64_internal (tp, __localtime64_r, &localtime64_offset); +} #if defined DEBUG_MKTIME && DEBUG_MKTIME