diff options
Diffstat (limited to 'lib/mktime.c')
| -rw-r--r-- | lib/mktime.c | 630 |
1 files changed, 630 insertions, 0 deletions
diff --git a/lib/mktime.c b/lib/mktime.c new file mode 100644 index 000000000..9eb3e7652 --- /dev/null +++ b/lib/mktime.c @@ -0,0 +1,630 @@ +/* Convert a 'struct tm' to a time_t value. + Copyright (C) 1993-2016 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 + <http://www.gnu.org/licenses/>. */ + +/* Define this to 1 to have a standalone program to test this implementation of + mktime. */ +#ifndef DEBUG_MKTIME +# define DEBUG_MKTIME 0 +#endif + +#if !defined _LIBC && !DEBUG_MKTIME +# include <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 <limits.h> +#include <stdbool.h> + +#include <intprops.h> +#include <verify.h> + +#if DEBUG_MKTIME +# include <stdio.h> +# include <stdlib.h> +# include <string.h> +/* Make it work even if the system's libc has its own mktime routine. */ +# undef mktime +# define mktime my_mktime +#endif + +/* A signed type that can represent an integer number of years + multiplied by three 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 three comes because these products need + to be subtracted from each other, and sometimes with an offset + added to them, without worrying about overflow. + + Much of the code uses long_int to represent time_t values, to + lessen the hassle of dealing with platforms where time_t is + unsigned, and because long_int should suffice to represent all + time_t values that mktime can generate even on platforms where + time_t is excessively wide. */ + +#if INT_MAX <= LONG_MAX / 3 / 366 / 24 / 60 / 60 +typedef long int long_int; +#else +typedef long long int long_int; +#endif +verify (INT_MAX <= TYPE_MAXIMUM (long_int) / 3 / 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 / (one << b) - (a % (one << b) < 0)); +} + +/* Bounds for the intersection of time_t and long_int. */ + +static long_int const mktime_min + = ((TYPE_SIGNED (time_t) && TYPE_MINIMUM (time_t) < TYPE_MINIMUM (long_int)) + ? TYPE_MINIMUM (long_int) : TYPE_MINIMUM (time_t)); +static long_int const mktime_max + = (TYPE_MAXIMUM (long_int) < TYPE_MAXIMUM (time_t) + ? TYPE_MAXIMUM (long_int) : TYPE_MAXIMUM (time_t)); + +verify (TYPE_IS_INTEGER (time_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 } + }; + + +#ifdef _LIBC +typedef time_t mktime_offset_t; +#else +/* Portable standalone applications should supply a <time.h> that + declares a POSIX-compliant localtime_r, for the benefit of older + implementations that lack localtime_r or have a nonstandard one. + See the gnulib time_r module for one way to implement this. */ +# undef __localtime_r +# define __localtime_r localtime_r +# define __mktime_internal mktime_internal +# include "mktime-internal.h" +#endif + +/* 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 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 overflow + when multiplied by three times the number of seconds in a year, and + likewise for YDAY1 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 / 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 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 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. + 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 the returned value would be out of range, yield the minimal or + maximal in-range value, except do not yield a value equal to T. */ +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) +{ + 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; + } + + /* 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 < long_int_avg (mktime_min, mktime_max) + ? (t <= mktime_min + 1 ? t + 1 : mktime_min) + : (mktime_max - 1 <= t ? t - 1 : mktime_max)); +} + +/* 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. */ +static struct tm * +convert_time (struct tm *(*convert) (const time_t *, struct tm *), + long_int t, struct tm *tm) +{ + time_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 time_t and long_int. */ +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 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; + } + + if (!r && ok) + { + /* The last conversion attempt failed; + revert to the most recent successful attempt. */ + r = convert_time (convert, ok, 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. + This function is external because it is used also by timegm.c. */ +time_t +__mktime_internal (struct tm *tp, + struct tm *(*convert) (const time_t *, struct tm *), + mktime_offset_t *offset) +{ + long_int t, gt, t0, t1, t2, dt; + 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 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; + + int negative_offset_guess; + + 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. */ + + INT_SUBTRACT_WRAPV (0, *offset, &negative_offset_guess); + t0 = ydhms_diff (year, yday, hour, min, sec, + EPOCH_YEAR - TM_YEAR_BASE, 0, 0, 0, negative_offset_guess); + + /* 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) + 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) + { + long_int ot; + if (! INT_ADD_WRAPV (t, delta * direction, &ot)) + { + struct tm otm; + ranged_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_time_tm (year, yday, hour, min, sec, ot, &otm); + ranged_convert (convert, &t, &tm); + goto offset_found; + } + } + } + } + + 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, &dt); + INT_SUBTRACT_WRAPV (dt, 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) + || ! convert_time (convert, t, &tm)) + return -1; + } + + *tp = tm; + return t; +} + + +static mktime_offset_t localtime_offset; + +/* Convert *TP to a time_t value. */ +time_t +mktime (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 (); +#elif HAVE_TZSET + tzset (); +#endif + + return __mktime_internal (tp, __localtime_r, &localtime_offset); +} + +#ifdef weak_alias +weak_alias (mktime, timelocal) +#endif + +#ifdef _LIBC +libc_hidden_def (mktime) +libc_hidden_weak (timelocal) +#endif + +#if DEBUG_MKTIME + +static int +not_equal_tm (const struct tm *a, const struct tm *b) +{ + return ((a->tm_sec ^ b->tm_sec) + | (a->tm_min ^ b->tm_min) + | (a->tm_hour ^ b->tm_hour) + | (a->tm_mday ^ b->tm_mday) + | (a->tm_mon ^ b->tm_mon) + | (a->tm_year ^ b->tm_year) + | (a->tm_yday ^ b->tm_yday) + | isdst_differ (a->tm_isdst, b->tm_isdst)); +} + +static void +print_tm (const struct tm *tp) +{ + if (tp) + printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d", + tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday, + tp->tm_hour, tp->tm_min, tp->tm_sec, + tp->tm_yday, tp->tm_wday, tp->tm_isdst); + else + printf ("0"); +} + +static int +check_result (time_t tk, struct tm tmk, time_t tl, const struct tm *lt) +{ + if (tk != tl || !lt || not_equal_tm (&tmk, lt)) + { + printf ("mktime ("); + print_tm (lt); + printf (")\nyields ("); + print_tm (&tmk); + printf (") == %ld, should be %ld\n", (long int) tk, (long int) tl); + return 1; + } + + return 0; +} + +int +main (int argc, char **argv) +{ + int status = 0; + struct tm tm, tmk, tml; + struct tm *lt; + time_t tk, tl, tl1; + char trailer; + + /* Sanity check, plus call tzset. */ + tl = 0; + if (! localtime (&tl)) + { + printf ("localtime (0) fails\n"); + status = 1; + } + + if ((argc == 3 || argc == 4) + && (sscanf (argv[1], "%d-%d-%d%c", + &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer) + == 3) + && (sscanf (argv[2], "%d:%d:%d%c", + &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer) + == 3)) + { + tm.tm_year -= TM_YEAR_BASE; + tm.tm_mon--; + tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]); + tmk = tm; + tl = mktime (&tmk); + lt = localtime_r (&tl, &tml); + printf ("mktime returns %ld == ", (long int) tl); + print_tm (&tmk); + printf ("\n"); + status = check_result (tl, tmk, tl, lt); + } + else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0)) + { + time_t from = atol (argv[1]); + time_t by = atol (argv[2]); + time_t to = atol (argv[3]); + + if (argc == 4) + for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1) + { + lt = localtime_r (&tl, &tml); + if (lt) + { + tmk = tml; + tk = mktime (&tmk); + status |= check_result (tk, tmk, tl, &tml); + } + else + { + printf ("localtime_r (%ld) yields 0\n", (long int) tl); + status = 1; + } + tl1 = tl + by; + if ((tl1 < tl) != (by < 0)) + break; + } + else + for (tl = from; by < 0 ? to <= tl : tl <= to; tl = tl1) + { + /* Null benchmark. */ + lt = localtime_r (&tl, &tml); + if (lt) + { + tmk = tml; + tk = tl; + status |= check_result (tk, tmk, tl, &tml); + } + else + { + printf ("localtime_r (%ld) yields 0\n", (long int) tl); + status = 1; + } + tl1 = tl + by; + if ((tl1 < tl) != (by < 0)) + break; + } + } + else + printf ("Usage:\ +\t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\ +\t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\ +\t%s FROM BY TO - # Do not test those values (for benchmark).\n", + argv[0], argv[0], argv[0]); + + return status; +} + +#endif /* DEBUG_MKTIME */ + +/* +Local Variables: +compile-command: "gcc -DDEBUG_MKTIME -I. -Wall -W -O2 -g mktime.c -o mktime" +End: +*/ |