time/mktime.c

   1 /* Convert a `struct tm' to a time_t value.
   2    Copyright (C) 1993-1999, 2002 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Paul Eggert (eggert@twinsun.com).
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 /* Define this to have a standalone program to test this implementation of
  22    mktime.  */
  23 /* #define DEBUG 1 */
  24
  25 #ifdef HAVE_CONFIG_H
  26 # include <config.h>
  27 #endif
  28
  29 #ifdef _LIBC
  30 # define HAVE_LIMITS_H 1
  31 # define STDC_HEADERS 1
  32 #endif
  33
  34 /* Assume that leap seconds are possible, unless told otherwise.
  35    If the host has a `zic' command with a `-L leapsecondfilename' option,
  36    then it supports leap seconds; otherwise it probably doesn't.  */
  37 #ifndef LEAP_SECONDS_POSSIBLE
  38 # define LEAP_SECONDS_POSSIBLE 1
  39 #endif
  40
  41 #include <sys/types.h>          /* Some systems define `time_t' here.  */
  42 #include <time.h>
  43
  44 #if HAVE_LIMITS_H
  45 # include <limits.h>
  46 #endif
  47
  48 #if DEBUG
  49 # include <stdio.h>
  50 # if STDC_HEADERS
  51 #  include <stdlib.h>
  52 #  include <string.h>
  53 # endif
  54 /* Make it work even if the system's libc has its own mktime routine.  */
  55 # define mktime my_mktime
  56 #endif /* DEBUG */
  57
  58 #ifndef __P
  59 # if defined __GNUC__ || (defined __STDC__ && __STDC__)
  60 #  define __P(args) args
  61 # else
  62 #  define __P(args) ()
  63 # endif  /* GCC.  */
  64 #endif  /* Not __P.  */
  65
  66 #ifndef CHAR_BIT
  67 # define CHAR_BIT 8
  68 #endif
  69
  70 /* The extra casts work around common compiler bugs.  */
  71 #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
  72 /* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
  73    It is necessary at least when t == time_t.  */
  74 #define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
  75                               ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
  76 #define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))
  77
  78 #ifndef INT_MIN
  79 # define INT_MIN TYPE_MINIMUM (int)
  80 #endif
  81 #ifndef INT_MAX
  82 # define INT_MAX TYPE_MAXIMUM (int)
  83 #endif
  84
  85 #ifndef TIME_T_MIN
  86 # define TIME_T_MIN TYPE_MINIMUM (time_t)
  87 #endif
  88 #ifndef TIME_T_MAX
  89 # define TIME_T_MAX TYPE_MAXIMUM (time_t)
  90 #endif
  91
  92 #define TM_YEAR_BASE 1900
  93 #define EPOCH_YEAR 1970
  94
  95 #ifndef __isleap
  96 /* Nonzero if YEAR is a leap year (every 4 years,
  97    except every 100th isn't, and every 400th is).  */
  98 # define __isleap(year) \
  99   ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
 100 #endif
 101
 102 /* How many days come before each month (0-12).  */
 103 const unsigned short int __mon_yday[2][13] =
 104   {
 105     /* Normal years.  */
 106     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
 107     /* Leap years.  */
 108     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
 109   };
 110
 111
 112 #ifdef _LIBC
 113 # define my_mktime_localtime_r __localtime_r
 114 #else
 115 /* If we're a mktime substitute in a GNU program, then prefer
 116    localtime to localtime_r, since many localtime_r implementations
 117    are buggy.  */
 118 static struct tm *
 119 my_mktime_localtime_r (const time_t *t, struct tm *tp)
 120 {
 121   struct tm *l = localtime (t);
 122   if (! l)
 123     return 0;
 124   *tp = *l;
 125   return tp;
 126 }
 127 #endif /* ! _LIBC */
 128
 129
 130 /* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
 131    measured in seconds, ignoring leap seconds.
 132    YEAR uses the same numbering as TM->tm_year.
 133    All values are in range, except possibly YEAR.
 134    If TP is null, return a nonzero value.
 135    If overflow occurs, yield the low order bits of the correct answer.  */
 136 static time_t
 137 ydhms_tm_diff (int year, int yday, int hour, int min, int sec,
 138                const struct tm *tp)
 139 {
 140   if (!tp)
 141     return 1;
 142   else
 143     {
 144       /* Compute intervening leap days correctly even if year is negative.
 145          Take care to avoid int overflow.  time_t overflow is OK, since
 146          only the low order bits of the correct time_t answer are needed.
 147          Don't convert to time_t until after all divisions are done, since
 148          time_t might be unsigned.  */
 149       int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
 150       int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
 151       int a100 = a4 / 25 - (a4 % 25 < 0);
 152       int b100 = b4 / 25 - (b4 % 25 < 0);
 153       int a400 = a100 >> 2;
 154       int b400 = b100 >> 2;
 155       int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
 156       time_t years = year - (time_t) tp->tm_year;
 157       time_t days = (365 * years + intervening_leap_days
 158                      + (yday - tp->tm_yday));
 159       return (60 * (60 * (24 * days + (hour - tp->tm_hour))
 160                     + (min - tp->tm_min))
 161               + (sec - tp->tm_sec));
 162     }
 163 }
 164
 165 /* Use CONVERT to convert *T to a broken down time in *TP.
 166    If *T is out of range for conversion, adjust it so that
 167    it is the nearest in-range value and then convert that.  */
 168 static struct tm *
 169 ranged_convert (struct tm *(*convert) (const time_t *, struct tm *),
 170                 time_t *t, struct tm *tp)
 171 {
 172   struct tm *r;
 173
 174   if (! (r = (*convert) (t, tp)) && *t)
 175     {
 176       time_t bad = *t;
 177       time_t ok = 0;
 178       struct tm tm;
 179
 180       /* BAD is a known unconvertible time_t, and OK is a known good one.
 181          Use binary search to narrow the range between BAD and OK until
 182          they differ by 1.  */
 183       while (bad != ok + (bad < 0 ? -1 : 1))
 184         {
 185           time_t mid = *t = (bad < 0
 186                              ? bad + ((ok - bad) >> 1)
 187                              : ok + ((bad - ok) >> 1));
 188           if ((r = (*convert) (t, tp)))
 189             {
 190               tm = *r;
 191               ok = mid;
 192             }
 193           else
 194             bad = mid;
 195         }
 196
 197       if (!r && ok)
 198         {
 199           /* The last conversion attempt failed;
 200              revert to the most recent successful attempt.  */
 201           *t = ok;
 202           *tp = tm;
 203           r = tp;
 204         }
 205     }
 206
 207   return r;
 208 }
 209
 210
 211 /* Convert *TP to a time_t value, inverting
 212    the monotonic and mostly-unit-linear conversion function CONVERT.
 213    Use *OFFSET to keep track of a guess at the offset of the result,
 214    compared to what the result would be for UTC without leap seconds.
 215    If *OFFSET's guess is correct, only one CONVERT call is needed.  */
 216 time_t
 217 __mktime_internal (struct tm *tp,
 218                    struct tm *(*convert) (const time_t *, struct tm *),
 219                    time_t *offset)
 220 {
 221   time_t t, dt, t0, t1, t2;
 222   struct tm tm;
 223
 224   /* The maximum number of probes (calls to CONVERT) should be enough
 225      to handle any combinations of time zone rule changes, solar time,
 226      leap seconds, and oscillations around a spring-forward gap.
 227      POSIX.1 prohibits leap seconds, but some hosts have them anyway.  */
 228   int remaining_probes = 6;
 229
 230   /* Time requested.  Copy it in case CONVERT modifies *TP; this can
 231      occur if TP is localtime's returned value and CONVERT is localtime.  */
 232   int sec = tp->tm_sec;
 233   int min = tp->tm_min;
 234   int hour = tp->tm_hour;
 235   int mday = tp->tm_mday;
 236   int mon = tp->tm_mon;
 237   int year_requested = tp->tm_year;
 238   int isdst = tp->tm_isdst;
 239
 240   /* 1 if the previous probe was DST.  */
 241   int dst2;
 242
 243   /* Ensure that mon is in range, and set year accordingly.  */
 244   int mon_remainder = mon % 12;
 245   int negative_mon_remainder = mon_remainder < 0;
 246   int mon_years = mon / 12 - negative_mon_remainder;
 247   int year = year_requested + mon_years;
 248
 249   /* Only years after 1970 are defined.  */
 250   if (year < 70)
 251     return -1;
 252
 253    /* The other values need not be in range:
 254      the remaining code handles minor overflows correctly,
 255      assuming int and time_t arithmetic wraps around.
 256      Major overflows are caught at the end.  */
 257
 258   /* Calculate day of year from year, month, and day of month.
 259      The result need not be in range.  */
 260   int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
 261                [mon_remainder + 12 * negative_mon_remainder])
 262               + mday - 1);
 263
 264   int sec_requested = sec;
 265 #if LEAP_SECONDS_POSSIBLE
 266   /* Handle out-of-range seconds specially,
 267      since ydhms_tm_diff assumes every minute has 60 seconds.  */
 268   if (sec < 0)
 269     sec = 0;
 270   if (59 < sec)
 271     sec = 59;
 272 #endif
 273
 274   /* Invert CONVERT by probing.  First assume the same offset as last time.
 275      Then repeatedly use the error to improve the guess.  */
 276
 277   tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
 278   tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
 279   t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
 280
 281   for (t = t1 = t2 = t0 + *offset, dst2 = 0;
 282        (dt = ydhms_tm_diff (year, yday, hour, min, sec,
 283                             ranged_convert (convert, &t, &tm)));
 284        t1 = t2, t2 = t, t += dt, dst2 = tm.tm_isdst != 0)
 285     if (t == t1 && t != t2
 286         && (tm.tm_isdst < 0
 287             || (isdst < 0
 288                 ? dst2 <= (tm.tm_isdst != 0)
 289                 : (isdst != 0) != (tm.tm_isdst != 0))))
 290       /* We can't possibly find a match, as we are oscillating
 291          between two values.  The requested time probably falls
 292          within a spring-forward gap of size DT.  Follow the common
 293          practice in this case, which is to return a time that is DT
 294          away from the requested time, preferring a time whose
 295          tm_isdst differs from the requested value.  (If no tm_isdst
 296          was requested and only one of the two values has a nonzero
 297          tm_isdst, prefer that value.)  In practice, this is more
 298          useful than returning -1.  */
 299       break;
 300     else if (--remaining_probes == 0)
 301       return -1;
 302
 303   /* If we have a match, check whether tm.tm_isdst has the requested
 304      value, if any.  */
 305   if (dt == 0 && isdst != tm.tm_isdst && 0 <= isdst && 0 <= tm.tm_isdst)
 306     {
 307       /* tm.tm_isdst has the wrong value.  Look for a neighboring
 308          time with the right value, and use its UTC offset.
 309          Heuristic: probe the previous three calendar quarters (approximately),
 310          looking for the desired isdst.  This isn't perfect,
 311          but it's good enough in practice.  */
 312       int quarter = 7889238; /* seconds per average 1/4 Gregorian year */
 313       int i;
 314
 315       /* If we're too close to the time_t limit, look in future quarters.  */
 316       if (t < TIME_T_MIN + 3 * quarter)
 317         quarter = -quarter;
 318
 319       for (i = 1; i <= 3; i++)
 320         {
 321           time_t ot = t - i * quarter;
 322           struct tm otm;
 323           ranged_convert (convert, &ot, &otm);
 324           if (otm.tm_isdst == isdst)
 325             {
 326               /* We found the desired tm_isdst.
 327                  Extrapolate back to the desired time.  */
 328               t = ot + ydhms_tm_diff (year, yday, hour, min, sec, &otm);
 329               ranged_convert (convert, &t, &tm);
 330               break;
 331             }
 332         }
 333     }
 334
 335   *offset = t - t0;
 336
 337 #if LEAP_SECONDS_POSSIBLE
 338   if (sec_requested != tm.tm_sec)
 339     {
 340       /* Adjust time to reflect the tm_sec requested, not the normalized value.
 341          Also, repair any damage from a false match due to a leap second.  */
 342       t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
 343       if (! (*convert) (&t, &tm))
 344         return -1;
 345     }
 346 #endif
 347
 348   if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
 349     {
 350       /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
 351          so check for major overflows.  A gross check suffices,
 352          since if t has overflowed, it is off by a multiple of
 353          TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
 354          the difference that is bounded by a small value.  */
 355
 356       double dyear = (double) year_requested + mon_years - tm.tm_year;
 357       double dday = 366 * dyear + mday;
 358       double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
 359
 360       /* On Irix4.0.5 cc, dividing TIME_T_MIN by 3 does not produce
 361          correct results, ie., it erroneously gives a positive value
 362          of 715827882.  Setting a variable first then doing math on it
 363          seems to work.  (ghazi@caip.rutgers.edu) */
 364
 365       const time_t time_t_max = TIME_T_MAX;
 366       const time_t time_t_min = TIME_T_MIN;
 367
 368       if (time_t_max / 3 - time_t_min / 3 < (dsec < 0 ? - dsec : dsec))
 369         return -1;
 370     }
 371
 372   *tp = tm;
 373   return t;
 374 }
 375
 376
 377 static time_t localtime_offset;
 378
 379 /* Convert *TP to a time_t value.  */
 380 time_t
 381 mktime (tp)
 382      struct tm *tp;
 383 {
 384 #ifdef _LIBC
 385   /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
 386      time zone names contained in the external variable `tzname' shall
 387      be set as if the tzset() function had been called.  */
 388   __tzset ();
 389 #endif
 390
 391   return __mktime_internal (tp, my_mktime_localtime_r, &localtime_offset);
 392 }
 393
 394 #ifdef weak_alias
 395 weak_alias (mktime, timelocal)
 396 #endif
 397 \f
 398 #if DEBUG
 399
 400 static int
 401 not_equal_tm (a, b)
 402      struct tm *a;
 403      struct tm *b;
 404 {
 405   return ((a->tm_sec ^ b->tm_sec)
 406           | (a->tm_min ^ b->tm_min)
 407           | (a->tm_hour ^ b->tm_hour)
 408           | (a->tm_mday ^ b->tm_mday)
 409           | (a->tm_mon ^ b->tm_mon)
 410           | (a->tm_year ^ b->tm_year)
 411           | (a->tm_mday ^ b->tm_mday)
 412           | (a->tm_yday ^ b->tm_yday)
 413           | (a->tm_isdst ^ b->tm_isdst));
 414 }
 415
 416 static void
 417 print_tm (tp)
 418      struct tm *tp;
 419 {
 420   if (tp)
 421     printf ("%04d-%02d-%02d %02d:%02d:%02d yday %03d wday %d isdst %d",
 422             tp->tm_year + TM_YEAR_BASE, tp->tm_mon + 1, tp->tm_mday,
 423             tp->tm_hour, tp->tm_min, tp->tm_sec,
 424             tp->tm_yday, tp->tm_wday, tp->tm_isdst);
 425   else
 426     printf ("0");
 427 }
 428
 429 static int
 430 check_result (tk, tmk, tl, lt)
 431      time_t tk;
 432      struct tm tmk;
 433      time_t tl;
 434      struct tm *lt;
 435 {
 436   if (tk != tl || !lt || not_equal_tm (&tmk, lt))
 437     {
 438       printf ("mktime (");
 439       print_tm (&tmk);
 440       printf (")\nyields (");
 441       print_tm (lt);
 442       printf (") == %ld, should be %ld\n", (long) tl, (long) tk);
 443       return 1;
 444     }
 445
 446   return 0;
 447 }
 448
 449 int
 450 main (argc, argv)
 451      int argc;
 452      char **argv;
 453 {
 454   int status = 0;
 455   struct tm tm, tmk, tml;
 456   struct tm *lt;
 457   time_t tk, tl;
 458   char trailer;
 459
 460   if ((argc == 3 || argc == 4)
 461       && (sscanf (argv[1], "%d-%d-%d%c",
 462                   &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &trailer)
 463           == 3)
 464       && (sscanf (argv[2], "%d:%d:%d%c",
 465                   &tm.tm_hour, &tm.tm_min, &tm.tm_sec, &trailer)
 466           == 3))
 467     {
 468       tm.tm_year -= TM_YEAR_BASE;
 469       tm.tm_mon--;
 470       tm.tm_isdst = argc == 3 ? -1 : atoi (argv[3]);
 471       tmk = tm;
 472       tl = mktime (&tmk);
 473       lt = localtime (&tl);
 474       if (lt)
 475         {
 476           tml = *lt;
 477           lt = &tml;
 478         }
 479       printf ("mktime returns %ld == ", (long) tl);
 480       print_tm (&tmk);
 481       printf ("\n");
 482       status = check_result (tl, tmk, tl, lt);
 483     }
 484   else if (argc == 4 || (argc == 5 && strcmp (argv[4], "-") == 0))
 485     {
 486       time_t from = atol (argv[1]);
 487       time_t by = atol (argv[2]);
 488       time_t to = atol (argv[3]);
 489
 490       if (argc == 4)
 491         for (tl = from; tl <= to; tl += by)
 492           {
 493             lt = localtime (&tl);
 494             if (lt)
 495               {
 496                 tmk = tml = *lt;
 497                 tk = mktime (&tmk);
 498                 status |= check_result (tk, tmk, tl, tml);
 499               }
 500             else
 501               {
 502                 printf ("localtime (%ld) yields 0\n", (long) tl);
 503                 status = 1;
 504               }
 505           }
 506       else
 507         for (tl = from; tl <= to; tl += by)
 508           {
 509             /* Null benchmark.  */
 510             lt = localtime (&tl);
 511             if (lt)
 512               {
 513                 tmk = tml = *lt;
 514                 tk = tl;
 515                 status |= check_result (tk, tmk, tl, tml);
 516               }
 517             else
 518               {
 519                 printf ("localtime (%ld) yields 0\n", (long) tl);
 520                 status = 1;
 521               }
 522           }
 523     }
 524   else
 525     printf ("Usage:\
 526 \t%s YYYY-MM-DD HH:MM:SS [ISDST] # Test given time.\n\
 527 \t%s FROM BY TO # Test values FROM, FROM+BY, ..., TO.\n\
 528 \t%s FROM BY TO - # Do not test those values (for benchmark).\n",
 529             argv[0], argv[0], argv[0]);
 530
 531   return status;
 532 }
 533
 534 #endif /* DEBUG */
 535 \f
 536 /*
 537 Local Variables:
 538 compile-command: "gcc -DDEBUG -DHAVE_LIMITS_H -DSTDC_HEADERS -Wall -W -O -g mktime.c -o mktime"
 539 End:
 540 */