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Diffstat (limited to 'lib/mktime.c')
| -rw-r--r-- | lib/mktime.c | 578 |
1 files changed, 578 insertions, 0 deletions
diff --git a/lib/mktime.c b/lib/mktime.c new file mode 100644 index 0000000..7dc9d67 --- /dev/null +++ b/lib/mktime.c @@ -0,0 +1,578 @@ +/* Convert a 'struct tm' to a time_t value. + Copyright (C) 1993-2022 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, see + <https://www.gnu.org/licenses/>. */ + +/* The following macros influence what gets defined when this file is compiled: + + Macro/expression Which gnulib module This compilation unit + should define + + _LIBC (glibc proper) mktime + + NEED_MKTIME_WORKING mktime rpl_mktime + || NEED_MKTIME_WINDOWS + + NEED_MKTIME_INTERNAL mktime-internal mktime_internal + */ + +#ifndef _LIBC +# include <libc-config.h> +#endif + +/* Assume that leap seconds are possible, unless told otherwise. + If the host has a 'zic' command with a '-L leapsecondfilename' option, + then it supports leap seconds; otherwise it probably doesn't. */ +#ifndef LEAP_SECONDS_POSSIBLE +# define LEAP_SECONDS_POSSIBLE 1 +#endif + +#include <time.h> + +#include <errno.h> +#include <limits.h> +#include <stdbool.h> +#include <stdlib.h> +#include <string.h> + +#include <intprops.h> +#include <verify.h> + +#ifndef NEED_MKTIME_INTERNAL +# define NEED_MKTIME_INTERNAL 0 +#endif +#ifndef NEED_MKTIME_WINDOWS +# define NEED_MKTIME_WINDOWS 0 +#endif +#ifndef NEED_MKTIME_WORKING +# define NEED_MKTIME_WORKING 0 +#endif + +#include "mktime-internal.h" + +#if !defined _LIBC && (NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS) +static void +my_tzset (void) +{ +# if NEED_MKTIME_WINDOWS + /* Rectify the value of the environment variable TZ. + There are four possible kinds of such values: + - Traditional US time zone names, e.g. "PST8PDT". Syntax: see + <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset> + - Time zone names based on geography, that contain one or more + slashes, e.g. "Europe/Moscow". + - Time zone names based on geography, without slashes, e.g. + "Singapore". + - Time zone names that contain explicit DST rules. Syntax: see + <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03> + The Microsoft CRT understands only the first kind. It produces incorrect + results if the value of TZ is of the other kinds. + But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value + of the second kind for most geographies, or of the first kind in a few + other geographies. If it is of the second kind, neutralize it. For the + Microsoft CRT, an absent or empty TZ means the time zone that the user + has set in the Windows Control Panel. + If the value of TZ is of the third or fourth kind -- Cygwin programs + understand these syntaxes as well --, it does not matter whether we + neutralize it or not, since these values occur only when a Cygwin user + has set TZ explicitly; this case is 1. rare and 2. under the user's + responsibility. */ + const char *tz = getenv ("TZ"); + if (tz != NULL && strchr (tz, '/') != NULL) + _putenv ("TZ="); +# else + tzset (); +# endif +} +# undef __tzset +# define __tzset() my_tzset () +#endif + +#if defined _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL + +/* A signed type that can represent an integer number of years + multiplied by four times the number of seconds in a year. It is + needed when converting a tm_year value times the number of seconds + in a year. The factor of four comes because these products need + to be subtracted from each other, and sometimes with an offset + added to them, and then with another timestamp added, without + worrying about overflow. + + Much of the code uses long_int to represent __time64_t values, to + lessen the hassle of dealing with platforms where __time64_t is + unsigned, and because long_int should suffice to represent all + __time64_t values that mktime can generate even on platforms where + __time64_t is wider than the int components of struct tm. */ + +#if INT_MAX <= LONG_MAX / 4 / 366 / 24 / 60 / 60 +typedef long int long_int; +#else +typedef long long int long_int; +#endif +verify (INT_MAX <= TYPE_MAXIMUM (long_int) / 4 / 366 / 24 / 60 / 60); + +/* Shift A right by B bits portably, by dividing A by 2**B and + truncating towards minus infinity. B should be in the range 0 <= B + <= LONG_INT_BITS - 2, where LONG_INT_BITS is the number of useful + bits in a long_int. LONG_INT_BITS is at least 32. + + ISO C99 says that A >> B is implementation-defined if A < 0. Some + implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift + right in the usual way when A < 0, so SHR falls back on division if + ordinary A >> B doesn't seem to be the usual signed shift. */ + +static long_int +shr (long_int a, int b) +{ + long_int one = 1; + return (-one >> 1 == -1 + ? a >> b + : (a + (a < 0)) / (one << b) - (a < 0)); +} + +/* Bounds for the intersection of __time64_t and long_int. */ + +static long_int const mktime_min + = ((TYPE_SIGNED (__time64_t) + && TYPE_MINIMUM (__time64_t) < TYPE_MINIMUM (long_int)) + ? TYPE_MINIMUM (long_int) : TYPE_MINIMUM (__time64_t)); +static long_int const mktime_max + = (TYPE_MAXIMUM (long_int) < TYPE_MAXIMUM (__time64_t) + ? TYPE_MAXIMUM (long_int) : TYPE_MAXIMUM (__time64_t)); + +#define EPOCH_YEAR 1970 +#define TM_YEAR_BASE 1900 +verify (TM_YEAR_BASE % 100 == 0); + +/* Is YEAR + TM_YEAR_BASE a leap year? */ +static bool +leapyear (long_int year) +{ + /* Don't add YEAR to TM_YEAR_BASE, as that might overflow. + Also, work even if YEAR is negative. */ + return + ((year & 3) == 0 + && (year % 100 != 0 + || ((year / 100) & 3) == (- (TM_YEAR_BASE / 100) & 3))); +} + +/* How many days come before each month (0-12). */ +#ifndef _LIBC +static +#endif +const unsigned short int __mon_yday[2][13] = + { + /* Normal years. */ + { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 }, + /* Leap years. */ + { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 } + }; + + +/* Do the values A and B differ according to the rules for tm_isdst? + A and B differ if one is zero and the other positive. */ +static bool +isdst_differ (int a, int b) +{ + return (!a != !b) && (0 <= a) && (0 <= b); +} + +/* 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 timestamps. + + The YEAR values uses the same numbering as TP->tm_year. Values + need not be in the usual range. However, YEAR1 - YEAR0 must not + overflow even when multiplied by three times the number of seconds + in a year, and likewise for YDAY1 - YDAY0 and three times the + number of seconds in a day. */ + +static long_int +ydhms_diff (long_int year1, long_int yday1, int hour1, int min1, int sec1, + int year0, int yday0, int hour0, int min0, int sec0) +{ + verify (-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 + (a4 < 0)) / 25 - (a4 < 0); + int b100 = (b4 + (b4 < 0)) / 25 - (b4 < 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 without overflowing. */ + long_int years = year1 - year0; + long_int days = 365 * years + yday1 - yday0 + intervening_leap_days; + long_int hours = 24 * days + hour1 - hour0; + long_int minutes = 60 * hours + min1 - min0; + long_int seconds = 60 * minutes + sec1 - sec0; + return seconds; +} + +/* Return the average of A and B, even if A + B would overflow. + Round toward positive infinity. */ +static long_int +long_int_avg (long_int a, long_int b) +{ + return shr (a, 1) + shr (b, 1) + ((a | b) & 1); +} + +/* 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. + *TP should be in the usual range. */ +static long_int +tm_diff (long_int year, long_int yday, int hour, int min, int sec, + struct tm const *tp) +{ + 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 __time64_t. Return TM if successful, NULL (setting errno) on + failure. */ +static struct tm * +convert_time (struct tm *(*convert) (const __time64_t *, struct tm *), + long_int t, struct tm *tm) +{ + __time64_t x = t; + return convert (&x, 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 __time64_t and long_int. + Return TP on success, NULL (setting errno) on failure. */ +static struct tm * +ranged_convert (struct tm *(*convert) (const __time64_t *, struct tm *), + long_int *t, struct tm *tp) +{ + long_int t1 = (*t < mktime_min ? mktime_min + : *t <= mktime_max ? *t : mktime_max); + struct tm *r = convert_time (convert, t1, tp); + if (r) + { + *t = t1; + return r; + } + if (errno != EOVERFLOW) + return NULL; + + long_int bad = t1; + long_int ok = 0; + struct tm oktm; oktm.tm_sec = -1; + + /* 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; + } + + if (oktm.tm_sec < 0) + return NULL; + *t = ok; + *tp = oktm; + return tp; +} + + +/* 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. + If successful, set *TP to the canonicalized struct tm; + otherwise leave *TP alone, return ((time_t) -1) and set errno. + This function is external because it is used also by timegm.c. */ +__time64_t +__mktime_internal (struct tm *tp, + struct tm *(*convert) (const __time64_t *, struct tm *), + mktime_offset_t *offset) +{ + 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 = 0; + + /* 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 overflows correctly. */ + + /* 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; + + mktime_offset_t off = *offset; + int negative_offset_guess; + + int sec_requested = sec; + + if (LEAP_SECONDS_POSSIBLE) + { + /* Handle out-of-range seconds specially, + since ydhms_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. */ + + INT_SUBTRACT_WRAPV (0, off, &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. */ + + 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. */ + 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. If none is found within a + reasonable duration bound, assume a one-hour DST difference. + This should work for all real time zone histories in the tz + database. */ + + /* +1 if we wanted standard time but got DST, -1 if the reverse. */ + int dst_difference = (isdst == 0) - (tm.tm_isdst == 0); + + /* 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; + + /* In TZDB 2021e, the longest period of DST (or of non-DST), in + which the DST (or adjacent DST) difference is not one hour, + is 457243209 seconds: e.g., America/Cambridge_Bay with leap + seconds, starting 1965-10-31 00:00 in a switch from + double-daylight time (-05) to standard time (-07), and + continuing to 1980-04-27 02:00 in a switch from standard time + (-07) to daylight time (-06). */ + int duration_max = 457243209; + + /* 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) + { + long_int ot; + if (! INT_ADD_WRAPV (t, delta * direction, &ot)) + { + struct tm 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. */ + 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; + } + } + } + } + + /* No unusual DST offset was found nearby. Assume one-hour DST. */ + t += 60 * 60 * dst_difference; + if (mktime_min <= t && t <= mktime_max && convert_time (convert, t, &tm)) + goto offset_found; + + __set_errno (EOVERFLOW); + return -1; + } + + offset_found: + /* Set *OFFSET to the low-order bits of T - T0 - NEGATIVE_OFFSET_GUESS. + This is just a heuristic to speed up the next mktime call, and + correctness is unaffected if integer overflow occurs here. */ + INT_SUBTRACT_WRAPV (t, t0, offset); + INT_SUBTRACT_WRAPV (*offset, negative_offset_guess, offset); + + 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. */ + long_int sec_adjustment = sec == 0 && tm.tm_sec == 60; + sec_adjustment -= sec; + sec_adjustment += sec_requested; + if (INT_ADD_WRAPV (t, sec_adjustment, &t) + || ! (mktime_min <= t && t <= mktime_max)) + { + __set_errno (EOVERFLOW); + return -1; + } + if (! convert_time (convert, t, &tm)) + return -1; + } + + *tp = tm; + return t; +} + +#endif /* _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_INTERNAL */ + +#if defined _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS + +/* Convert *TP to a __time64_t value. */ +__time64_t +__mktime64 (struct tm *tp) +{ + /* 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 (); + +# if defined _LIBC || NEED_MKTIME_WORKING + static mktime_offset_t localtime_offset; + return __mktime_internal (tp, __localtime64_r, &localtime_offset); +# else +# undef mktime + return mktime (tp); +# endif +} +#endif /* _LIBC || NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS */ + +#if defined _LIBC && __TIMESIZE != 64 + +libc_hidden_def (__mktime64) + +time_t +mktime (struct tm *tp) +{ + struct tm tm = *tp; + __time64_t t = __mktime64 (&tm); + if (in_time_t_range (t)) + { + *tp = tm; + return t; + } + else + { + __set_errno (EOVERFLOW); + return -1; + } +} + +#endif + +weak_alias (mktime, timelocal) +libc_hidden_def (mktime) +libc_hidden_weak (timelocal) |