bug#19874: 25.0.50; encode-time not working as expected

[Paul Eggert <eggert@cs.ucla.edu>]

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Ashish SHUKLA wrote:
> When I looked into this before filing this bug report, from what I noticed
> that it's not using libc's `mktime' function, unlike what you seem to
> indicate. I'm not sure quite why it's doing that when libc provided mktime
> works just fine

It may work for this example, but 'configure' checks for a number of mktime 
bugs, and perhaps mktime is not working for some other examples.

Is 'configure' setting APPLE_UNIVERSAL_BUILD to 1, or to 0?  You can tell by 
looking for APPLE_UNIVERSAL_BUILD in lib/Makefile.

When 'configure' says 'checking for working mktime', what's the result?

If you compile and run the attached program, using the same flags that you use 
to build Emacs, what is its exit status?


[-- Attachment #2: mktime-test.c --]
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#define HAVE_UNISTD_H 1
#define HAVE_DECL_ALARM 1

/* Test program from Paul Eggert and Tony Leneis.  */
#include <limits.h>
#include <stdlib.h>
#include <time.h>

#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif

#if HAVE_DECL_ALARM
# include <signal.h>
#endif

/* Work around redefinition to rpl_putenv by other config tests.  */
#undef putenv

static time_t time_t_max;
static time_t time_t_min;

/* Values we'll use to set the TZ environment variable.  */
static char *tz_strings[] = {
  (char *) 0, "TZ=GMT0", "TZ=JST-9",
  "TZ=EST+3EDT+2,M10.1.0/00:00:00,M2.3.0/00:00:00"
};
#define N_STRINGS (sizeof (tz_strings) / sizeof (tz_strings[0]))

/* Return 0 if mktime fails to convert a date in the spring-forward gap.
   Based on a problem report from Andreas Jaeger.  */
static int
spring_forward_gap ()
{
  /* glibc (up to about 1998-10-07) failed this test. */
  struct tm tm;

  /* Use the portable POSIX.1 specification "TZ=PST8PDT,M4.1.0,M10.5.0"
     instead of "TZ=America/Vancouver" in order to detect the bug even
     on systems that don't support the Olson extension, or don't have the
     full zoneinfo tables installed.  */
  putenv ("TZ=PST8PDT,M4.1.0,M10.5.0");

  tm.tm_year = 98;
  tm.tm_mon = 3;
  tm.tm_mday = 5;
  tm.tm_hour = 2;
  tm.tm_min = 0;
  tm.tm_sec = 0;
  tm.tm_isdst = -1;
  return mktime (&tm) != (time_t) -1;
}

static int
mktime_test1 (time_t now)
{
  struct tm *lt;
  return ! (lt = localtime (&now)) || mktime (lt) == now;
}

static int
mktime_test (time_t now)
{
  return (mktime_test1 (now)
          && mktime_test1 ((time_t) (time_t_max - now))
          && mktime_test1 ((time_t) (time_t_min + now)));
}

static int
irix_6_4_bug ()
{
  /* Based on code from Ariel Faigon.  */
  struct tm tm;
  tm.tm_year = 96;
  tm.tm_mon = 3;
  tm.tm_mday = 0;
  tm.tm_hour = 0;
  tm.tm_min = 0;
  tm.tm_sec = 0;
  tm.tm_isdst = -1;
  mktime (&tm);
  return tm.tm_mon == 2 && tm.tm_mday == 31;
}

static int
bigtime_test (int j)
{
  struct tm tm;
  time_t now;
  tm.tm_year = tm.tm_mon = tm.tm_mday = tm.tm_hour = tm.tm_min = tm.tm_sec = j;
  now = mktime (&tm);
  if (now != (time_t) -1)
    {
      struct tm *lt = localtime (&now);
      if (! (lt
             && lt->tm_year == tm.tm_year
             && lt->tm_mon == tm.tm_mon
             && lt->tm_mday == tm.tm_mday
             && lt->tm_hour == tm.tm_hour
             && lt->tm_min == tm.tm_min
             && lt->tm_sec == tm.tm_sec
             && lt->tm_yday == tm.tm_yday
             && lt->tm_wday == tm.tm_wday
             && ((lt->tm_isdst < 0 ? -1 : 0 < lt->tm_isdst)
                  == (tm.tm_isdst < 0 ? -1 : 0 < tm.tm_isdst))))
        return 0;
    }
  return 1;
}

static int
year_2050_test ()
{
  /* The correct answer for 2050-02-01 00:00:00 in Pacific time,
     ignoring leap seconds.  */
  unsigned long int answer = 2527315200UL;

  struct tm tm;
  time_t t;
  tm.tm_year = 2050 - 1900;
  tm.tm_mon = 2 - 1;
  tm.tm_mday = 1;
  tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
  tm.tm_isdst = -1;

  /* Use the portable POSIX.1 specification "TZ=PST8PDT,M4.1.0,M10.5.0"
     instead of "TZ=America/Vancouver" in order to detect the bug even
     on systems that don't support the Olson extension, or don't have the
     full zoneinfo tables installed.  */
  putenv ("TZ=PST8PDT,M4.1.0,M10.5.0");

  t = mktime (&tm);

  /* Check that the result is either a failure, or close enough
     to the correct answer that we can assume the discrepancy is
     due to leap seconds.  */
  return (t == (time_t) -1
          || (0 < t && answer - 120 <= t && t <= answer + 120));
}

int
main ()
{
  int result = 0;
  time_t t, delta;
  int i, j;
  int time_t_signed_magnitude = (time_t) ~ (time_t) 0 < (time_t) -1;
  int time_t_signed = ! ((time_t) 0 < (time_t) -1);

#if HAVE_DECL_ALARM
  /* This test makes some buggy mktime implementations loop.
     Give up after 60 seconds; a mktime slower than that
     isn't worth using anyway.  */
  signal (SIGALRM, SIG_DFL);
  alarm (60);
#endif

  time_t_max = (! time_t_signed
                ? (time_t) -1
                : ((((time_t) 1 << (sizeof (time_t) * CHAR_BIT - 2)) - 1)
                   * 2 + 1));
  time_t_min = (! time_t_signed
                ? (time_t) 0
                : time_t_signed_magnitude
                ? ~ (time_t) 0
                : ~ time_t_max);

  delta = time_t_max / 997; /* a suitable prime number */
  for (i = 0; i < N_STRINGS; i++)
    {
      if (tz_strings[i])
        putenv (tz_strings[i]);

      for (t = 0; t <= time_t_max - delta && (result & 1) == 0; t += delta)
        if (! mktime_test (t))
          result |= 1;
      if ((result & 2) == 0
          && ! (mktime_test ((time_t) 1)
                && mktime_test ((time_t) (60 * 60))
                && mktime_test ((time_t) (60 * 60 * 24))))
        result |= 2;

      for (j = 1; (result & 4) == 0; j <<= 1)
        {
          if (! bigtime_test (j))
            result |= 4;
          if (INT_MAX / 2 < j)
            break;
        }
      if ((result & 8) == 0 && ! bigtime_test (INT_MAX))
        result |= 8;
    }
  if (! irix_6_4_bug ())
    result |= 16;
  if (! spring_forward_gap ())
    result |= 32;
  if (! year_2050_test ())
    result |= 64;
  return result;
}