src/mktime.c

   1 /* Convert a `struct tm' to a time_t value.
   2    Copyright (C) 1993, 94, 95, 96, 97, 98, 99 Free Software Foundation, Inc.
   3    Contributed by Paul Eggert (eggert@twinsun.com).
   4
   5    NOTE: The canonical source of this file is maintained with the GNU C Library.
   6    Bugs can be reported to bug-glibc@gnu.org.
   7
   8    This program is free software; you can redistribute it and/or modify it
   9    under the terms of the GNU General Public License as published by the
  10    Free Software Foundation; either version 2, or (at your option) any
  11    later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  21    USA.  */
  22
  23 /* Define this to have a standalone program to test this implementation of
  24    mktime.  */
  25 /* #define DEBUG 1 */
  26
  27 #ifdef HAVE_CONFIG_H
  28 # include <config.h>
  29 #endif
  30
  31 #ifdef _LIBC
  32 # define HAVE_LIMITS_H 1
  33 # define STDC_HEADERS 1
  34 #endif
  35
  36 /* Assume that leap seconds are possible, unless told otherwise.
  37    If the host has a `zic' command with a `-L leapsecondfilename' option,
  38    then it supports leap seconds; otherwise it probably doesn't.  */
  39 #ifndef LEAP_SECONDS_POSSIBLE
  40 # define LEAP_SECONDS_POSSIBLE 1
  41 #endif
  42
  43 #include <sys/types.h>          /* Some systems define `time_t' here.  */
  44 #include <time.h>
  45
  46 #if HAVE_LIMITS_H
  47 # include <limits.h>
  48 #endif
  49
  50 #if DEBUG
  51 # include <stdio.h>
  52 # if STDC_HEADERS
  53 #  include <stdlib.h>
  54 # endif
  55 /* Make it work even if the system's libc has its own mktime routine.  */
  56 # define mktime my_mktime
  57 #endif /* DEBUG */
  58
  59 #ifndef __P
  60 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
  61 #  define __P(args) args
  62 # else
  63 #  define __P(args) ()
  64 # endif  /* GCC.  */
  65 #endif  /* Not __P.  */
  66
  67 #ifndef CHAR_BIT
  68 # define CHAR_BIT 8
  69 #endif
  70
  71 /* The extra casts work around common compiler bugs.  */
  72 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  73 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
  74    It is necessary at least when t == time_t.  */
  75 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  76                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
  77 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  78
  79 #ifndef INT_MIN
  80 # define INT_MIN TYPE_MINIMUM (int)
  81 #endif
  82 #ifndef INT_MAX
  83 # define INT_MAX TYPE_MAXIMUM (int)
  84 #endif
  85
  86 #ifndef TIME_T_MIN
  87 # define TIME_T_MIN TYPE_MINIMUM (time_t)
  88 #endif
  89 #ifndef TIME_T_MAX
  90 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
  91 #endif
  92
  93 #define TM_YEAR_BASE 1900
  94 #define EPOCH_YEAR 1970
  95
  96 #ifndef __isleap
  97 /* Nonzero if YEAR is a leap year (every 4 years,
  98    except every 100th isn't, and every 400th is).  */
  99 # define __isleap(year) \
 100   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
 101 #endif
 102
 103 /* How many days come before each month (0-12).  */
 104 const unsigned short int __mon_yday[2][13] =
 105   {
 106     /* Normal years.  */
 107     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
 108     /* Leap years.  */
 109     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
 110   };
 111
 112
 113 #ifdef _LIBC
 114 # define my_mktime_localtime_r __localtime_r
 115 #else
 116 /* If we're a mktime substitute in a GNU program, then prefer
 117    localtime to localtime_r, since many localtime_r implementations
 118    are buggy.  */
 119 static struct tm *
 120 my_mktime_localtime_r (t, tp)
 121      const time_t *t;
 122      struct tm *tp;
 123 {
 124   struct tm *l = localtime (t);
 125   if (! l)
 126     return 0;
 127   *tp = *l;
 128   return tp;
 129 }
 130 #endif /* ! _LIBC */
 131
 132
 133 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
 134    measured in seconds, ignoring leap seconds.
 135    YEAR uses the same numbering as TM->tm_year.
 136    All values are in range, except possibly YEAR.
 137    If TP is null, return a nonzero value.
 138    If overflow occurs, yield the low order bits of the correct answer.  */
 139 static time_t
 140 ydhms_tm_diff (year, yday, hour, min, sec, tp)
 141      int year, yday, hour, min, sec;
 142      const struct tm *tp;
 143 {
 144   if (!tp)
 145     return 1;
 146   else
 147     {
 148       /* Compute intervening leap days correctly even if year is negative.
 149          Take care to avoid int overflow.  time_t overflow is OK, since
 150          only the low order bits of the correct time_t answer are needed.
 151          Don't convert to time_t until after all divisions are done, since
 152          time_t might be unsigned.  */
 153       int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
 154       int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
 155       int a100 = a4 / 25 - (a4 % 25 < 0);
 156       int b100 = b4 / 25 - (b4 % 25 < 0);
 157       int a400 = a100 >> 2;
 158       int b400 = b100 >> 2;
 159       int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
 160       time_t years = year - (time_t) tp->tm_year;
 161       time_t days = (365 * years + intervening_leap_days
 162                      + (yday - tp->tm_yday));
 163       return (60 * (60 * (24 * days + (hour - tp->tm_hour))
 164                     + (min - tp->tm_min))
 165               + (sec - tp->tm_sec));
 166     }
 167 }
 168
 169 /* Use CONVERT to convert *T to a broken down time in *TP.
 170    If *T is out of range for conversion, adjust it so that
 171    it is the nearest in-range value and then convert that.  */
 172 static struct tm *
 173 ranged_convert (convert, t, tp)
 174 #ifdef PROTOTYPES
 175      struct tm *(*convert) (const time_t *, struct tm *);
 176 #else
 177      struct tm *(*convert)();
 178 #endif
 179      time_t *t;
 180      struct tm *tp;
 181 {
 182   struct tm *r;
 183
 184   if (! (r = (*convert) (t, tp)) && *t)
 185     {
 186       time_t bad = *t;
 187       time_t ok = 0;
 188       struct tm tm;
 189
 190       /* BAD is a known unconvertible time_t, and OK is a known good one.
 191          Use binary search to narrow the range between BAD and OK until
 192          they differ by 1.  */
 193       while (bad != ok + (bad < 0 ? -1 : 1))
 194         {
 195           time_t mid = *t = (bad < 0
 196                              ? bad + ((ok - bad) >> 1)
 197                              : ok + ((bad - ok) >> 1));
 198           if ((r = (*convert) (t, tp)))
 199             {
 200               tm = *r;
 201               ok = mid;
 202             }
 203           else
 204             bad = mid;
 205         }
 206
 207       if (!r && ok)
 208         {
 209           /* The last conversion attempt failed;
 210              revert to the most recent successful attempt.  */
 211           *t = ok;
 212           *tp = tm;
 213           r = tp;
 214         }
 215     }
 216
 217   return r;
 218 }
 219
 220
 221 /* Convert *TP to a time_t value, inverting
 222    the monotonic and mostly-unit-linear conversion function CONVERT.
 223    Use *OFFSET to keep track of a guess at the offset of the result,
 224    compared to what the result would be for UTC without leap seconds.
 225    If *OFFSET's guess is correct, only one CONVERT call is needed.  */
 226 time_t
 227 __mktime_internal (tp, convert, offset)
 228      struct tm *tp;
 229 #ifdef PROTOTYPES
 230      struct tm *(*convert) (const time_t *, struct tm *);
 231 #else
 232      struct tm *(*convert)();
 233 #endif
 234      time_t *offset;
 235 {
 236   time_t t, dt, t0, t1, t2;
 237   struct tm tm;
 238
 239   /* The maximum number of probes (calls to CONVERT) should be enough
 240      to handle any combinations of time zone rule changes, solar time,
 241      leap seconds, and oscillations around a spring-forward gap.
 242      POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
 243   int remaining_probes = 6;
 244
 245   /* Time requested.  Copy it in case CONVERT modifies *TP; this can
 246      occur if TP is localtime's returned value and CONVERT is localtime.  */
 247   int sec = tp->tm_sec;
 248   int min = tp->tm_min;
 249   int hour = tp->tm_hour;
 250   int mday = tp->tm_mday;
 251   int mon = tp->tm_mon;
 252   int year_requested = tp->tm_year;
 253   int isdst = tp->tm_isdst;
 254
 255   /* Ensure that mon is in range, and set year accordingly.  */
 256   int mon_remainder = mon % 12;
 257   int negative_mon_remainder = mon_remainder < 0;
 258   int mon_years = mon / 12 - negative_mon_remainder;
 259   int year = year_requested + mon_years;
 260
 261   /* The other values need not be in range:
 262      the remaining code handles minor overflows correctly,
 263      assuming int and time_t arithmetic wraps around.
 264      Major overflows are caught at the end.  */
 265
 266   /* Calculate day of year from year, month, and day of month.
 267      The result need not be in range.  */
 268   int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
 269                [mon_remainder + 12 * negative_mon_remainder])
 270               + mday - 1);
 271
 272   int sec_requested = sec;
 273 #if LEAP_SECONDS_POSSIBLE
 274   /* Handle out-of-range seconds specially,
 275      since ydhms_tm_diff assumes every minute has 60 seconds.  */
 276   if (sec < 0)
 277     sec = 0;
 278   if (59 < sec)
 279     sec = 59;
 280 #endif
 281
 282   /* Invert CONVERT by probing.  First assume the same offset as last time.
 283      Then repeatedly use the error to improve the guess.  */
 284
 285   tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
 286   tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
 287   t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
 288
 289   for (t = t1 = t2 = t0 + *offset;
 290        (dt = ydhms_tm_diff (year, yday, hour, min, sec,
 291                             ranged_convert (convert, &t, &tm)));
 292        t1 = t2, t2 = t, t += dt)
 293     if (t == t1 && t != t2
 294         && (isdst < 0 || tm.tm_isdst < 0
 295             || (isdst != 0) != (tm.tm_isdst != 0)))
 296       /* We can't possibly find a match, as we are oscillating
 297          between two values.  The requested time probably falls
 298          within a spring-forward gap of size DT.  Follow the common
 299          practice in this case, which is to return a time that is DT
 300          away from the requested time, preferring a time whose
 301          tm_isdst differs from the requested value.  In practice,
 302          this is more useful than returning -1.  */
 303       break;
 304     else if (--remaining_probes == 0)
 305       return -1;
 306
 307   /* If we have a match, check whether tm.tm_isdst has the requested
 308      value, if any.  */
 309   if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
 310     {
 311       /* tm.tm_isdst has the wrong value.  Look for a neighboring
 312          time with the right value, and use its UTC offset.
 313          Heuristic: probe the previous three calendar quarters (approximately),
 314          looking for the desired isdst.  This isn't perfect,
 315          but it's good enough in practice.  */
 316       int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
 317       int i;
 318
 319       /* If we're too close to the time_t limit, look in future quarters.  */
 320       if (t < TIME_T_MIN + 3 * quarter)
 321         quarter = -quarter;
 322
 323       for (i = 1; i <= 3; i++)
 324         {
 325           time_t ot = t - i * quarter;
 326           struct tm otm;
 327           ranged_convert (convert, &ot, &otm);
 328           if (otm.tm_isdst == isdst)
 329             {
 330               /* We found the desired tm_isdst.
 331                  Extrapolate back to the desired time.  */
 332               t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
 333               ranged_convert (convert, &t, &tm);
 334               break;
 335             }
 336         }
 337     }
 338
 339   *offset = t - t0;
 340
 341 #if LEAP_SECONDS_POSSIBLE
 342   if (sec_requested != tm.tm_sec)
 343     {
 344       /* Adjust time to reflect the tm_sec requested, not the normalized value.
 345          Also, repair any damage from a false match due to a leap second.  */
 346       t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
 347       if (! (*convert) (&t, &tm))
 348         return -1;
 349     }
 350 #endif
 351
 352   if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
 353     {
 354       /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
 355          so check for major overflows.  A gross check suffices,
 356          since if t has overflowed, it is off by a multiple of
 357          TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
 358          the difference that is bounded by a small value.  */
 359
 360       double dyear = (double) year_requested + mon_years - tm.tm_year;
 361       double dday = 366 * dyear + mday;
 362       double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
 363
 364       /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
 365          correct results, ie., it erroneously gives a positive value
 366          of 715827882.  Setting a variable first then doing math on it
 367          seems to work.  (ghazi@caip.rutgers.edu) */
 368
 369       const time_t time_t_max = TIME_T_MAX;
 370       const time_t time_t_min = TIME_T_MIN;
 371
 372       if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
 373         return -1;
 374     }
 375
 376   *tp = tm;
 377   return t;
 378 }
 379
 380
 381 static time_t localtime_offset;
 382
 383 /* Convert *TP to a time_t value.  */
 384 time_t
 385 mktime (tp)
 386      struct tm *tp;
 387 {
 388 #ifdef _LIBC
 389   /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
 390      time zone names contained in the external variable `tzname' shall
 391      be set as if the tzset() function had been called.  */
 392   __tzset ();
 393 #endif
 394
 395   return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
 396 }
 397
 398 #ifdef weak_alias
 399 weak_alias (mktime, timelocal)
 400 #endif
 401 \f
 402 #if DEBUG
 403
 404 static int
 405 not_equal_tm (a, b)
 406      struct tm *a;
 407      struct tm *b;
 408 {
 409   return ((a->tm_sec ^ b->tm_sec)
 410           | (a->tm_min ^ b->tm_min)
 411           | (a->tm_hour ^ b->tm_hour)
 412           | (a->tm_mday ^ b->tm_mday)
 413           | (a->tm_mon ^ b->tm_mon)
 414           | (a->tm_year ^ b->tm_year)
 415           | (a->tm_mday ^ b->tm_mday)
 416           | (a->tm_yday ^ b->tm_yday)
 417           | (a->tm_isdst ^ b->tm_isdst));
 418 }
 419
 420 static void
 421 print_tm (tp)
 422      struct tm *tp;
 423 {
 424   if (tp)
 425     printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
 426             tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
 427             tp->tm_hour, tp->tm_min, tp->tm_sec,
 428             tp->tm_yday, tp->tm_wday, tp->tm_isdst);
 429   else
 430     printf ("0");
 431 }
 432
 433 static int
 434 check_result (tk, tmk, tl, lt)
 435      time_t tk;
 436      struct tm tmk;
 437      time_t tl;
 438      struct tm *lt;
 439 {
 440   if (tk != tl || !lt || not_equal_tm (&tmk, lt))
 441     {
 442       printf ("mktime (");
 443       print_tm (&tmk);
 444       printf (")\nyields (");
 445       print_tm (lt);
 446       printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
 447       return 1;
 448     }
 449
 450   return 0;
 451 }
 452
 453 int
 454 main (argc, argv)
 455      int argc;
 456      char **argv;
 457 {
 458   int status = 0;
 459   struct tm tm, tmk, tml;
 460   struct tm *lt;
 461   time_t tk, tl;
 462   char trailer;
 463
 464   if ((argc == 3 || argc == 4)
 465       && (sscanf (argv[1], "%d-%d-%d%c",
 466                   &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
 467           == 3)
 468       && (sscanf (argv[2], "%d:%d:%d%c",
 469                   &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
 470           == 3))
 471     {
 472       tm.tm_year -= TM_YEAR_BASE;
 473       tm.tm_mon--;
 474       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
 475       tmk = tm;
 476       tl = mktime (&tmk);
 477       lt = localtime (&tl);
 478       if (lt)
 479         {
 480           tml = *lt;
 481           lt = &tml;
 482         }
 483       printf ("mktime returns %ld == ", (long) tl);
 484       print_tm (&tmk);
 485       printf ("\n");
 486       status = check_result (tl, tmk, tl, lt);
 487     }
 488   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
 489     {
 490       time_t from = atol (argv[1]);
 491       time_t by = atol (argv[2]);
 492       time_t to = atol (argv[3]);
 493
 494       if (argc == 4)
 495         for (tl = from; tl <= to; tl += by)
 496           {
 497             lt = localtime (&tl);
 498             if (lt)
 499               {
 500                 tmk = tml = *lt;
 501                 tk = mktime (&tmk);
 502                 status |= check_result (tk, tmk, tl, tml);
 503               }
 504             else
 505               {
 506                 printf ("localtime (%ld) yields 0\n", (long) tl);
 507                 status = 1;
 508               }
 509           }
 510       else
 511         for (tl = from; tl <= to; tl += by)
 512           {
 513             /* Null benchmark.  */
 514             lt = localtime (&tl);
 515             if (lt)
 516               {
 517                 tmk = tml = *lt;
 518                 tk = tl;
 519                 status |= check_result (tk, tmk, tl, tml);
 520               }
 521             else
 522               {
 523                 printf ("localtime (%ld) yields 0\n", (long) tl);
 524                 status = 1;
 525               }
 526           }
 527     }
 528   else
 529     printf ("Usage:\
 530 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
 531 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
 532 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
 533             argv[0], argv[0], argv[0]);
 534
 535   return status;
 536 }
 537
 538 #endif /* DEBUG */
 539 \f
 540 /*
 541 Local Variables:
 542 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
 543 End:
 544 */