/src/postgres/src/timezone/localtime.c

Source
/* Convert timestamp from pg_time_t to struct pg_tm.  */

/*
 * This file is in the public domain, so clarified as of
 * 1996-06-05 by Arthur David Olson.
 *
 * IDENTIFICATION
 *    src/timezone/localtime.c
 */

/*
 * Leap second handling from Bradley White.
 * POSIX.1-1988 style TZ environment variable handling from Guy Harris.
 */

/* this file needs to build in both frontend and backend contexts */
#include "c.h"

#include <fcntl.h>

#include "datatype/timestamp.h"
#include "pgtz.h"

#include "private.h"
#include "tzfile.h"


/*
 * Pacify gcc -Wcast-qual on char const * exprs.
 * Use this carefully, as the casts disable type checking.
 * This is a macro so that it can be used in static initializers.
 */
#define UNCONST(a) unconstify(char *, a)

#ifndef WILDABBR
/*
 * Someone might make incorrect use of a time zone abbreviation:
 *  1.  They might reference tzname[0] before calling tzset (explicitly
 *    or implicitly).
 *  2.  They might reference tzname[1] before calling tzset (explicitly
 *    or implicitly).
 *  3.  They might reference tzname[1] after setting to a time zone
 *    in which Daylight Saving Time is never observed.
 *  4.  They might reference tzname[0] after setting to a time zone
 *    in which Standard Time is never observed.
 *  5.  They might reference tm.TM_ZONE after calling offtime.
 * What's best to do in the above cases is open to debate;
 * for now, we just set things up so that in any of the five cases
 * WILDABBR is used. Another possibility: initialize tzname[0] to the
 * string "tzname[0] used before set", and similarly for the other cases.
 * And another: initialize tzname[0] to "ERA", with an explanation in the
 * manual page of what this "time zone abbreviation" means (doing this so
 * that tzname[0] has the "normal" length of three characters).
 */
#define WILDABBR "   "
#endif              /* !defined WILDABBR */

static const char wildabbr[] = WILDABBR;

/*
 * The DST rules to use if TZ has no rules.
 * Default to US rules as of 2017-05-07.
 * POSIX does not specify the default DST rules;
 * for historical reasons, US rules are a common default.
 */
#ifndef TZDEFRULESTRING
#define TZDEFRULESTRING ",M3.2.0,M11.1.0"
#endif

/* TZNAME_MAXIMUM and types ttinfo, lsinfo, state have been moved to pgtz.h */

static int
leapcount(ATTRIBUTE_MAYBE_UNUSED struct state const *sp)
{
#if TZ_RUNTIME_LEAPS
  return sp->leapcnt;
#else
  return 0;
#endif
}
static void
set_leapcount(ATTRIBUTE_MAYBE_UNUSED struct state *sp,
        ATTRIBUTE_MAYBE_UNUSED int leapcnt)
{
#if TZ_RUNTIME_LEAPS
  sp->leapcnt = leapcnt;
#endif
}
static struct lsinfo
lsinfo(ATTRIBUTE_MAYBE_UNUSED struct state const *sp,
     ATTRIBUTE_MAYBE_UNUSED int i)
{
#if TZ_RUNTIME_LEAPS
  return sp->lsis[i];
#else
  unreachable();
#endif
}
static void
set_lsinfo(ATTRIBUTE_MAYBE_UNUSED struct state *sp,
       ATTRIBUTE_MAYBE_UNUSED int i,
       ATTRIBUTE_MAYBE_UNUSED struct lsinfo lsinfo)
{
#if TZ_RUNTIME_LEAPS
  sp->lsis[i] = lsinfo;
#endif
}

enum r_type
{
  JULIAN_DAY,         /* Jn = Julian day */
  DAY_OF_YEAR,        /* n = day of year */
  MONTH_NTH_DAY_OF_WEEK   /* Mm.n.d = month, week, day of week */
};

struct rule
{
  enum r_type r_type;     /* type of rule */
  int     r_day;      /* day number of rule */
  int     r_week;     /* week number of rule */
  int     r_mon;      /* month number of rule */
  int_fast32_t r_time;    /* transition time of rule */
};

/*
 * Prototypes for static functions.
 */

static struct pg_tm *gmtsub(pg_time_t const *timep, int_fast32_t offset,
              struct pg_tm *tmp);
static bool increment_overflow(int *ip, int j);
static bool increment_overflow_time(pg_time_t *tp, int_fast32_2s j);
static int_fast32_2s leapcorr(struct state const *sp, pg_time_t t);
static struct pg_tm *timesub(pg_time_t const *timep,
               int_fast32_t offset, struct state const *sp,
               struct pg_tm *tmp);
static bool tzparse(const char *name, struct state *sp, struct state const *basep);


/*
 * Section 4.12.3 of X3.159-1989 requires that
 *  Except for the strftime function, these functions [asctime,
 *  ctime, gmtime, localtime] return values in one of two static
 *  objects: a broken-down time structure and an array of char.
 * Thanks to Paul Eggert for noting this.
 */

static struct pg_tm tm;

/* Initialize *S to a value based on UTOFF, ISDST, and DESIGIDX.  */
static void
init_ttinfo(struct ttinfo *s, int_fast32_t utoff, bool isdst,
      desigidx_type desigidx)
{
  s->tt_utoff = utoff;
  s->tt_isdst = isdst;
  s->tt_desigidx = desigidx;
  s->tt_ttisstd = false;
  s->tt_ttisut = false;
}

static int_fast32_2s
detzcode(const char *const codep)
{
  int     i;
  int_fast32_2s
        maxval = TWO_31_MINUS_1,
        minval = -1 - maxval,
        result;

  result = codep[0] & 0x7f;
  for (i = 1; i < 4; ++i)
    result = (result << 8) | (codep[i] & 0xff);

  if (codep[0] & 0x80)
  {
    /*
     * Do two's-complement negation even on non-two's-complement machines.
     * This cannot overflow, as int_fast32_2s is wide enough.
     */
    result += minval;
  }
  return result;
}

static int_fast64_t
detzcode64(const char *const codep)
{
  int_fast64_t result;
  int     i;
  int_fast64_t one = 1;
  int_fast64_t halfmaxval = one << (64 - 2);
  int_fast64_t maxval = halfmaxval - 1 + halfmaxval;
  int_fast64_t minval = -TWOS_COMPLEMENT(int_fast64_t) - maxval;

  result = codep[0] & 0x7f;
  for (i = 1; i < 8; ++i)
    result = (result << 8) | (codep[i] & 0xff);

  if (codep[0] & 0x80)
  {
    /*
     * Do two's-complement negation even on non-two's-complement machines.
     * If the result would be minval - 1, return minval.
     */
    result -= !TWOS_COMPLEMENT(int_fast64_t) && result != 0;
    result += minval;
  }
  return result;
}

/* Input buffer for data read from a compiled tz file.  */
union input_buffer
{
  /* The first part of the buffer, interpreted as a header.  */
  struct tzhead tzhead;

  /*
   * The entire buffer.  Ideally this would have no size limits; the
   * following should suffice for practical use.
   */
  char    buf[2 * sizeof(struct tzhead) + 2 * sizeof(struct state)
          + 4 * TZ_MAX_TIMES];
};

/* Local storage needed for 'tzloadbody'.  */
union local_storage
{
  /* The results of analyzing the file's contents after it is opened.  */
  struct file_analysis
  {
    /* The input buffer.  */
    union input_buffer u;

    /* A temporary state used for parsing a TZ string in the file.  */
    struct state st;
  }     u;

  /* PG: we don't need the "fullname" member */
};

/* These tzload flags can be ORed together, and fit into 'char'.  */
enum
{
TZLOAD_FROMENV = 1};      /* The TZ string came from the environment.  */
enum
{
TZLOAD_TZSTRING = 2};     /* Read any newline-surrounded TZ string.  */
enum
{
TZLOAD_TZDIR_SUB = 4};      /* TZ should be a file under TZDIR.  */

/*
 * Load tz data from the file named NAME into *SP.  Respect TZLOADFLAGS.
 * Use **LSPP for temporary storage.  Return 0 on
 * success, an errno value on failure.
 * PG: If "canonname" is not NULL, then on success the canonical spelling of
 * given name is stored there (the buffer must be > TZ_STRLEN_MAX bytes!).
 */
static int
tzloadbody(char const *name, char *canonname,
       struct state *sp, char tzloadflags,
       union local_storage **lspp)
{
  int     i;
  int     fid;
  int     stored;
  ssize_t   nread;
  union local_storage *lsp = *lspp;
  union input_buffer *up;
  int     tzheadsize = sizeof(struct tzhead);

  sp->goback = sp->goahead = false;

  if (!name)
  {
    name = TZDEFAULT;
    if (!name)
      return EINVAL;
  }

  if (name[0] == ':')
    ++name;

  /*
   * The IANA code goes to a great deal of trouble here to try to prevent
   * inappropriate file accesses.  That seems unnecessary for PG since we
   * won't run as root.  pg_open_tzfile() does go to some effort to prevent
   * accesses outside the designated zoneinfo tree, though.
   */
  fid = pg_open_tzfile(name, canonname);
  if (fid < 0)
    return ENOENT;     /* pg_open_tzfile may not set errno */

  up = &lsp->u.u;
  nread = read(fid, up->buf, sizeof up->buf);
  if (nread < tzheadsize)
  {
    int     err = nread < 0 ? errno : EINVAL;

    close(fid);
    return err;
  }
  if (close(fid) < 0)
    return errno;

  for (stored = 4; stored <= 8; stored *= 2)
  {
    char    version = up->tzhead.tzh_version[0];
    bool    skip_datablock = stored == 4 && version;
    int_fast32_t datablock_size;
    int_fast32_2s
          ttisstdcnt = detzcode(up->tzhead.tzh_ttisstdcnt),
          ttisutcnt = detzcode(up->tzhead.tzh_ttisutcnt),
          leapcnt = detzcode(up->tzhead.tzh_leapcnt),
          timecnt = detzcode(up->tzhead.tzh_timecnt),
          typecnt = detzcode(up->tzhead.tzh_typecnt),
          charcnt = detzcode(up->tzhead.tzh_charcnt);
    char const *p = up->buf + tzheadsize;

    /*
     * Although tzfile(5) currently requires typecnt to be nonzero,
     * support future formats that may allow zero typecnt in files that
     * have a TZ string and no transitions.
     */
    if (!(0 <= leapcnt
        && leapcnt <= (TZ_RUNTIME_LEAPS ? TZ_MAX_LEAPS : 0)
        && 0 <= typecnt && typecnt <= TZ_MAX_TYPES
        && 0 <= timecnt && timecnt <= TZ_MAX_TIMES
        && 0 <= charcnt && charcnt <= TZ_MAX_CHARS
        && 0 <= ttisstdcnt && ttisstdcnt <= TZ_MAX_TYPES
        && 0 <= ttisutcnt && ttisutcnt <= TZ_MAX_TYPES))
      return EINVAL;
    datablock_size
      = (timecnt * stored /* ats */
         + timecnt    /* types */
         + typecnt * 6  /* ttinfos */
         + charcnt    /* chars */
         + leapcnt * (stored + 4) /* lsinfos */
         + ttisstdcnt   /* ttisstds */
         + ttisutcnt);  /* ttisuts */
    if (nread < tzheadsize + datablock_size)
      return EINVAL;
    if (skip_datablock)
      p += datablock_size;
    else if (!((ttisstdcnt == typecnt || ttisstdcnt == 0)
           && (ttisutcnt == typecnt || ttisutcnt == 0)))
      return EINVAL;
    else
    {
      int_fast64_t prevtr = -1;
      int_fast32_2s prevcorr = -1;

      set_leapcount(sp, leapcnt);
      sp->timecnt = timecnt;
      sp->typecnt = typecnt;
      sp->charcnt = charcnt;

      /*
       * Read transitions, discarding those out of pg_time_t range. But
       * pretend the last transition before TIME_T_MIN occurred at
       * TIME_T_MIN.
       */
      timecnt = 0;
      for (i = 0; i < sp->timecnt; ++i)
      {
        int_fast64_t at
        = stored == 4 ? detzcode(p) : detzcode64(p);

        sp->types[i] = at <= TIME_T_MAX;
        if (sp->types[i])
        {
          pg_time_t attime
          = ((TYPE_SIGNED(pg_time_t) ? at < TIME_T_MIN : at < 0)
             ? TIME_T_MIN : at);

          if (timecnt && attime <= sp->ats[timecnt - 1])
          {
            if (attime < sp->ats[timecnt - 1])
              return EINVAL;
            sp->types[i - 1] = 0;
            timecnt--;
          }
          sp->ats[timecnt++] = attime;
        }
        p += stored;
      }

      timecnt = 0;
      for (i = 0; i < sp->timecnt; ++i)
      {
        unsigned char typ = *p++;

        if (sp->typecnt <= typ)
          return EINVAL;
        if (sp->types[i])
          sp->types[timecnt++] = typ;
      }
      sp->timecnt = timecnt;
      for (i = 0; i < sp->typecnt; ++i)
      {
        struct ttinfo *ttisp;
        unsigned char isdst,
              desigidx;
        int_fast32_2s utoff = detzcode(p);

        /*
         * Reject a UT offset equal to -2**31, as it might cause
         * trouble both in this file and in callers. Also, it violates
         * RFC 9636 section 3.2.
         */
        if (utoff < -TWO_31_MINUS_1)
          return EINVAL;

        ttisp = &sp->ttis[i];
        ttisp->tt_utoff = utoff;
        p += 4;
        isdst = *p++;
        if (!(isdst < 2))
          return EINVAL;
        ttisp->tt_isdst = isdst;
        desigidx = *p++;
        if (!(desigidx < sp->charcnt))
          return EINVAL;
        ttisp->tt_desigidx = desigidx;
      }
      for (i = 0; i < sp->charcnt; ++i)
        sp->chars[i] = *p++;

      /*
       * Ensure '\0'-terminated, and make it safe to call ttunspecified
       * later.
       */
      memset(&sp->chars[i], 0, CHARS_EXTRA);

      /* Read leap seconds, discarding those out of pg_time_t range.  */
      leapcnt = 0;
      for (i = 0; i < leapcount(sp); i++)
      {
        int_fast64_t tr = stored == 4 ? detzcode(p) : detzcode64(p);
        int_fast32_2s corr = detzcode(p + stored);

        p += stored + 4;

        /*
         * Leap seconds cannot occur before the Epoch, or out of
         * order.
         */
        if (tr <= prevtr)
          return EINVAL;

        /*
         * To avoid other botches in this code, each leap second's
         * correction must differ from the previous one's by 1 second
         * or less, except that the first correction can be any value;
         * these requirements are more generous than RFC 9636, to
         * allow future RFC extensions.
         */
        if (!(i == 0
            || (prevcorr < corr
              ? corr == prevcorr + 1
              : (corr == prevcorr
               || corr == prevcorr - 1))))
          return EINVAL;
        prevtr = tr;
        prevcorr = corr;

        if (tr <= TIME_T_MAX)
        {
          struct lsinfo ls;

          ls.ls_trans = tr;
          ls.ls_corr = corr;
          set_lsinfo(sp, leapcnt, ls);
          leapcnt++;
        }
      }
      set_leapcount(sp, leapcnt);

      for (i = 0; i < sp->typecnt; ++i)
      {
        struct ttinfo *ttisp;

        ttisp = &sp->ttis[i];
        if (ttisstdcnt == 0)
          ttisp->tt_ttisstd = false;
        else
        {
          if (*p != true && *p != false)
            return EINVAL;
          ttisp->tt_ttisstd = *p++;
        }
      }
      for (i = 0; i < sp->typecnt; ++i)
      {
        struct ttinfo *ttisp;

        ttisp = &sp->ttis[i];
        if (ttisutcnt == 0)
          ttisp->tt_ttisut = false;
        else
        {
          if (*p != true && *p != false)
            return EINVAL;
          ttisp->tt_ttisut = *p++;
        }
      }
    }

    nread -= p - up->buf;
    memmove(up->buf, p, nread);

    /* If this is an old file, we're done.  */
    if (!version)
      break;
  }
  if ((tzloadflags & TZLOAD_TZSTRING) && nread > 2 &&
    up->buf[0] == '\n' && up->buf[nread - 1] == '\n' &&
    sp->typecnt + 2 <= TZ_MAX_TYPES)
  {
    struct state *ts = &lsp->u.st;

    up->buf[nread - 1] = '\0';
    if (tzparse(&up->buf[1], ts, sp))
    {

      /*
       * Attempt to reuse existing abbreviations. Without this,
       * America/Anchorage would consume 50 bytes for abbreviations, as
       * sp->charcnt equals 40 (for LMT AST AWT APT AHST AHDT YST AKDT
       * AKST) and ts->charcnt equals 10 (for AKST AKDT).  Reusing means
       * sp->charcnt can stay 40 in this example.
       */
      int     gotabbr = 0;
      int     charcnt = sp->charcnt;

      for (i = 0; i < ts->typecnt; i++)
      {
        char     *tsabbr = ts->chars + ts->ttis[i].tt_desigidx;
        int     j;

        for (j = 0; j < charcnt; j++)
          if (strcmp(sp->chars + j, tsabbr) == 0)
          {
            ts->ttis[i].tt_desigidx = j;
            gotabbr++;
            break;
          }
        if (!(j < charcnt))
        {
          int     tsabbrlen = strnlen(tsabbr, TZ_MAX_CHARS - j);

          if (j + tsabbrlen < TZ_MAX_CHARS)
          {
            char     *cp = sp->chars + j;

            memcpy(cp, tsabbr, tsabbrlen);
            cp += tsabbrlen;
            *cp = '\0';
            charcnt = j + tsabbrlen + 1;
            ts->ttis[i].tt_desigidx = j;
            gotabbr++;
          }
        }
      }
      if (gotabbr == ts->typecnt)
      {
        sp->charcnt = charcnt;

        /*
         * Ignore any trailing, no-op transitions generated by zic as
         * they don't help here and can run afoul of bugs in zic 2016j
         * or earlier.
         */
        while (1 < sp->timecnt
             && (sp->types[sp->timecnt - 1]
               == sp->types[sp->timecnt - 2]))
          sp->timecnt--;

        sp->goahead = ts->goahead;

        for (i = 0; i < ts->timecnt; i++)
        {
          pg_time_t t = ts->ats[i];

          if (increment_overflow_time(&t, leapcorr(sp, t))
            || (0 < sp->timecnt
              && t <= sp->ats[sp->timecnt - 1]))
            continue;
          if (TZ_MAX_TIMES <= sp->timecnt)
          {
            sp->goahead = false;
            break;
          }
          sp->ats[sp->timecnt] = t;
          sp->types[sp->timecnt] = (sp->typecnt
                        + ts->types[i]);
          sp->timecnt++;
        }
        for (i = 0; i < ts->typecnt; i++)
          sp->ttis[sp->typecnt++] = ts->ttis[i];
      }
    }
  }
  if (sp->typecnt == 0)
    return EINVAL;

  return 0;
}

/*
 * Load tz data from the file named NAME into *SP.  Respect TZLOADFLAGS.
 * Return 0 on success, an errno value on failure.
 * PG: If "canonname" is not NULL, then on success the canonical spelling of
 * given name is stored there (the buffer must be > TZ_STRLEN_MAX bytes!).
 */
static int
tzload(char const *name, char *canonname, struct state *sp, char tzloadflags)
{
  /*
   * PG: by default, we allocate the "union local_storage" space via malloc,
   * since it's about 70kB which seems like a lot of stack space, and we're
   * hardly concerned about an extra malloc/free cycle here.  But under
   * USE_VALGRIND, put the variable on the stack, to intentionally increase
   * the amount of stack space allocated in the postmaster.  This prevents a
   * bad interaction between Valgrind and Python 3.14, for reasons that are
   * obscure and most likely no fault of ours.  Also note that unlike
   * upstream tzcode, our version of tzloadbody never reallocates *lspp.
   */
  int     r;
  union local_storage *lsp;
#ifdef USE_VALGRIND
  union local_storage ls;

  lsp = &ls;
#else
  lsp = malloc(sizeof *lsp);
  if (!lsp)
    return errno;
#endif
  r = tzloadbody(name, canonname, sp, tzloadflags, &lsp);
#ifndef USE_VALGRIND
  free(lsp);
#endif
  return r;
}

static const int mon_lengths[2][MONSPERYEAR] = {
  {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
  {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};

static const int year_lengths[2] = {
  DAYSPERNYEAR, DAYSPERLYEAR
};

/* Is C an ASCII digit?  */
static bool
is_digit(char c)
{
  return '0' <= c && c <= '9';
}

/*
 * Given a pointer into a timezone string, scan until a character that is not
 * a valid character in a time zone abbreviation is found.
 * Return a pointer to that character.
 */

ATTRIBUTE_PURE_114833 static const char *
getzname(const char *strp)
{
  char    c;

  while ((c = *strp) != '\0' && !is_digit(c) && c != ',' && c != '-' &&
       c != '+')
    ++strp;
  return strp;
}

/*
 * Given a pointer into an extended timezone string, scan until the ending
 * delimiter of the time zone abbreviation is located.
 * Return a pointer to the delimiter.
 *
 * As with getzname above, the legal character set is actually quite
 * restricted, with other characters producing undefined results.
 * We don't do any checking here; checking is done later in common-case code.
 */

ATTRIBUTE_PURE_114833 static const char *
getqzname(const char *strp, const int delim)
{
  int     c;

  while ((c = *strp) != '\0' && c != delim)
    ++strp;
  return strp;
}

/*
 * Given a pointer into a timezone string, extract a number from that string.
 * Check that the number is within a specified range; if it is not, return
 * NULL.
 * Otherwise, return a pointer to the first character not part of the number.
 */

static const char *
getnum(const char *strp, int *const nump, const int min, const int max)
{
  char    c;
  int     num;

  if (strp == NULL || !is_digit(c = *strp))
    return NULL;
  num = 0;
  do
  {
    num = num * 10 + (c - '0');
    if (num > max)
      return NULL;   /* illegal value */
    c = *++strp;
  } while (is_digit(c));
  if (num < min)
    return NULL;     /* illegal value */
  *nump = num;
  return strp;
}

/*
 * Given a pointer into a timezone string, extract a number of seconds,
 * in hh[:mm[:ss]] form, from the string.
 * If any error occurs, return NULL.
 * Otherwise, return a pointer to the first character not part of the number
 * of seconds.
 */

static const char *
getsecs(const char *strp, int_fast32_t *const secsp)
{
  int     num;
  int_fast32_t secsperhour = SECSPERHOUR;

  /*
   * 'HOURSPERDAY * DAYSPERWEEK - 1' allows quasi-POSIX rules like
   * "M10.4.6/26", which does not conform to POSIX, but which specifies the
   * equivalent of "02:00 on the first Sunday on or after 23 Oct".
   */
  strp = getnum(strp, &num, 0, HOURSPERDAY * DAYSPERWEEK - 1);
  if (strp == NULL)
    return NULL;
  *secsp = num * secsperhour;
  if (*strp == ':')
  {
    ++strp;
    strp = getnum(strp, &num, 0, MINSPERHOUR - 1);
    if (strp == NULL)
      return NULL;
    *secsp += num * SECSPERMIN;
    if (*strp == ':')
    {
      ++strp;
      /* 'SECSPERMIN' allows for leap seconds.  */
      strp = getnum(strp, &num, 0, SECSPERMIN);
      if (strp == NULL)
        return NULL;
      *secsp += num;
    }
  }
  return strp;
}

/*
 * Given a pointer into a timezone string, extract an offset, in
 * [+-]hh[:mm[:ss]] form, from the string.
 * If any error occurs, return NULL.
 * Otherwise, return a pointer to the first character not part of the time.
 */

static const char *
getoffset(const char *strp, int_fast32_t *const offsetp)
{
  bool    neg = false;

  if (*strp == '-')
  {
    neg = true;
    ++strp;
  }
  else if (*strp == '+')
    ++strp;
  strp = getsecs(strp, offsetp);
  if (strp == NULL)
    return NULL;     /* illegal time */
  if (neg)
    *offsetp = -*offsetp;
  return strp;
}

/*
 * Given a pointer into a timezone string, extract a rule in the form
 * date[/time]. See POSIX Base Definitions section 8.3 variable TZ
 * for the format of "date" and "time".
 * If a valid rule is not found, return NULL.
 * Otherwise, return a pointer to the first character not part of the rule.
 */

static const char *
getrule(const char *strp, struct rule *const rulep)
{
  if (*strp == 'J')
  {
    /*
     * Julian day.
     */
    rulep->r_type = JULIAN_DAY;
    ++strp;
    strp = getnum(strp, &rulep->r_day, 1, DAYSPERNYEAR);
  }
  else if (*strp == 'M')
  {
    /*
     * Month, week, day.
     */
    rulep->r_type = MONTH_NTH_DAY_OF_WEEK;
    ++strp;
    strp = getnum(strp, &rulep->r_mon, 1, MONSPERYEAR);
    if (strp == NULL)
      return NULL;
    if (*strp++ != '.')
      return NULL;
    strp = getnum(strp, &rulep->r_week, 1, 5);
    if (strp == NULL)
      return NULL;
    if (*strp++ != '.')
      return NULL;
    strp = getnum(strp, &rulep->r_day, 0, DAYSPERWEEK - 1);
  }
  else if (is_digit(*strp))
  {
    /*
     * Day of year.
     */
    rulep->r_type = DAY_OF_YEAR;
    strp = getnum(strp, &rulep->r_day, 0, DAYSPERLYEAR - 1);
  }
  else
    return NULL;     /* invalid format */
  if (strp == NULL)
    return NULL;
  if (*strp == '/')
  {
    /*
     * Time specified.
     */
    ++strp;
    strp = getoffset(strp, &rulep->r_time);
  }
  else
    rulep->r_time = 2 * SECSPERHOUR; /* default = 2:00:00 */
  return strp;
}

/*
 * Given a year, a rule, and the offset from UT at the time that rule takes
 * effect, calculate the year-relative time that rule takes effect.
 */

static int_fast32_t
transtime(const int year, const struct rule *const rulep,
      const int_fast32_t offset)
{
  bool    leapyear;
  int_fast32_t value;
  int     i;
  int     d,
        m1,
        yy0,
        yy1,
        yy2,
        dow;

  leapyear = isleap(year);
  switch (rulep->r_type)
  {

    case JULIAN_DAY:

      /*
       * Jn - Julian day, 1 == January 1, 60 == March 1 even in leap
       * years. In non-leap years, or if the day number is 59 or less,
       * just add SECSPERDAY times the day number-1 to the time of
       * January 1, midnight, to get the day.
       */
      value = (rulep->r_day - 1) * SECSPERDAY;
      if (leapyear && rulep->r_day >= 60)
        value += SECSPERDAY;
      break;

    case DAY_OF_YEAR:

      /*
       * n - day of year. Just add SECSPERDAY times the day number to
       * the time of January 1, midnight, to get the day.
       */
      value = rulep->r_day * SECSPERDAY;
      break;

    case MONTH_NTH_DAY_OF_WEEK:

      /*
       * Mm.n.d - nth "dth day" of month m.
       */

      /*
       * Use Zeller's Congruence to get day-of-week of first day of
       * month.
       */
      m1 = (rulep->r_mon + 9) % 12 + 1;
      yy0 = (rulep->r_mon <= 2) ? (year - 1) : year;
      yy1 = yy0 / 100;
      yy2 = yy0 % 100;
      dow = ((26 * m1 - 2) / 10 +
           1 + yy2 + yy2 / 4 + yy1 / 4 - 2 * yy1) % 7;
      if (dow < 0)
        dow += DAYSPERWEEK;

      /*
       * "dow" is the day-of-week of the first day of the month. Get the
       * day-of-month (zero-origin) of the first "dow" day of the month.
       */
      d = rulep->r_day - dow;
      if (d < 0)
        d += DAYSPERWEEK;
      for (i = 1; i < rulep->r_week; ++i)
      {
        if (d + DAYSPERWEEK >=
          mon_lengths[leapyear][rulep->r_mon - 1])
          break;
        d += DAYSPERWEEK;
      }

      /*
       * "d" is the day-of-month (zero-origin) of the day we want.
       */
      value = d * SECSPERDAY;
      for (i = 0; i < rulep->r_mon - 1; ++i)
        value += mon_lengths[leapyear][i] * SECSPERDAY;
      break;

    default:
      unreachable();
  }

  /*
   * "value" is the year-relative time of 00:00:00 UT on the day in
   * question. To get the year-relative time of the specified local time on
   * that day, add the transition time and the current offset from UT.
   */
  return value + rulep->r_time + offset;
}

/*
 * Given a POSIX.1 proleptic TZ string, fill in the rule tables as
 * appropriate.
 */

static bool
tzparse(const char *name, struct state *sp, struct state const *basep)
{
  const char *stdname;
  const char *dstname = NULL;
  int_fast32_t stdoffset;
  int_fast32_t dstoffset;
  char     *cp;
  ptrdiff_t stdlen,
        dstlen,
        charcnt;
  pg_time_t atlo = TIME_T_MIN,
        leaplo = TIME_T_MIN;

  stdname = name;
  if (*name == '<')
  {
    name++;
    stdname = name;
    name = getqzname(name, '>');
    if (*name != '>')
      return false;
    stdlen = name - stdname;
    name++;
  }
  else
  {
    name = getzname(name);
    stdlen = name - stdname;
  }
  if (stdlen > TZNAME_MAXIMUM)  /* allow empty STD abbrev, unlike IANA */
    return false;
  name = getoffset(name, &stdoffset);
  if (name == NULL)
    return false;
  charcnt = stdlen + 1;
  if (basep)
  {
    if (0 < basep->timecnt)
      atlo = basep->ats[basep->timecnt - 1];
    set_leapcount(sp, leapcount(basep));
    if (0 < leapcount(sp))
    {
      int     i;

      for (i = 0; i < leapcount(sp); i++)
        set_lsinfo(sp, i, lsinfo(basep, i));
      leaplo = lsinfo(sp, leapcount(sp) - 1).ls_trans;
    }
  }
  else
    set_leapcount(sp, 0); /* So, we're off a little.  */
  sp->goback = sp->goahead = false;
  if (*name != '\0')
  {
    struct rule start,
          end;
    int     year,
          yearbeg,
          yearlim,
          timecnt;
    pg_time_t janfirst;
    int_fast32_t janoffset = 0;

    if (*name == '<')
    {
      dstname = ++name;
      name = getqzname(name, '>');
      if (*name != '>')
        return false;
      dstlen = name - dstname;
      name++;
    }
    else
    {
      dstname = name;
      name = getzname(name);
      dstlen = name - dstname;  /* length of DST abbr. */
    }
    if (!(0 < dstlen && dstlen <= TZNAME_MAXIMUM))
      return false;
    charcnt += dstlen + 1;
    if (*name != '\0' && *name != ',' && *name != ';')
    {
      name = getoffset(name, &dstoffset);
      if (name == NULL)
        return false;
    }
    else
      dstoffset = stdoffset - SECSPERHOUR;

    if (*name == '\0')
      name = TZDEFRULESTRING;
    if (!(*name == ',' || *name == ';'))
      return false;

    name = getrule(name + 1, &start);
    if (!name)
      return false;
    if (*name++ != ',')
      return false;
    name = getrule(name, &end);
    if (!name || *name)
      return false;
    sp->typecnt = 2;    /* standard time and DST */

    /*
     * Two transitions per year, from EPOCH_YEAR forward.
     */
    init_ttinfo(&sp->ttis[0], -stdoffset, false, 0);
    init_ttinfo(&sp->ttis[1], -dstoffset, true, stdlen + 1);
    timecnt = 0;
    janfirst = 0;
    yearbeg = EPOCH_YEAR;

    do
    {
      int_fast32_t yearsecs
      = year_lengths[isleap(yearbeg - 1)] * SECSPERDAY;
      pg_time_t janfirst1 = janfirst;

      yearbeg--;
      if (increment_overflow_time(&janfirst1, -yearsecs))
      {
        janoffset = -yearsecs;
        break;
      }
      janfirst = janfirst1;
    } while (atlo < janfirst
         && EPOCH_YEAR - YEARSPERREPEAT / 2 < yearbeg);

    while (true)
    {
      int_fast32_t yearsecs
      = year_lengths[isleap(yearbeg)] * SECSPERDAY;
      int     yearbeg1 = yearbeg;
      pg_time_t janfirst1 = janfirst;

      if (increment_overflow_time(&janfirst1, yearsecs)
        || increment_overflow(&yearbeg1, 1)
        || atlo <= janfirst1)
        break;
      yearbeg = yearbeg1;
      janfirst = janfirst1;
    }

    yearlim = yearbeg;
    if (increment_overflow(&yearlim, years_of_observations))
      yearlim = INT_MAX;
    for (year = yearbeg; year < yearlim; year++)
    {
      int_fast32_t
            starttime = transtime(year, &start, stdoffset),
            endtime = transtime(year, &end, dstoffset),
            yearsecs = year_lengths[isleap(year)] * SECSPERDAY;
      bool    reversed = endtime < starttime;

      if (reversed)
      {
        int_fast32_t swap = starttime;

        starttime = endtime;
        endtime = swap;
      }
      if (reversed
        || (starttime < endtime
          && endtime - starttime < yearsecs))
      {
        if (TZ_MAX_TIMES - 2 < timecnt)
          break;
        sp->ats[timecnt] = janfirst;
        if (!increment_overflow_time(&sp->ats[timecnt],
                       janoffset + starttime)
          && atlo <= sp->ats[timecnt])
          sp->types[timecnt++] = !reversed;
        sp->ats[timecnt] = janfirst;
        if (!increment_overflow_time(&sp->ats[timecnt],
                       janoffset + endtime)
          && atlo <= sp->ats[timecnt])
        {
          sp->types[timecnt++] = reversed;
        }
      }
      if (endtime < leaplo)
      {
        yearlim = year;
        if (increment_overflow(&yearlim, years_of_observations))
          yearlim = INT_MAX;
      }
      if (increment_overflow_time(&janfirst, janoffset + yearsecs))
        break;
      janoffset = 0;
    }
    sp->timecnt = timecnt;
    if (!timecnt)
    {
      sp->ttis[0] = sp->ttis[1];
      sp->typecnt = 1;  /* Perpetual DST.  */
    }
    else if (years_of_observations <= year - yearbeg)
      sp->goback = sp->goahead = true;
  }
  else
  {
    dstlen = 0;
    sp->typecnt = 1;    /* only standard time */
    sp->timecnt = 0;
    init_ttinfo(&sp->ttis[0], -stdoffset, false, 0);
  }
  sp->charcnt = charcnt;
  cp = sp->chars;
  memcpy(cp, stdname, stdlen);
  cp += stdlen;
  *cp++ = '\0';
  if (dstlen != 0)
  {
    memcpy(cp, dstname, dstlen);
    cp += dstlen;
    *cp = '\0';
  }
  return true;
}

static void
gmtload(struct state *const sp)
{
  /* PG: for historical compatibility, use "GMT" not "UTC" as TZ abbrev */
  tzparse("GMT0", sp, NULL);
}


/*
 * The easy way to behave "as if no library function calls" localtime
 * is to not call it, so we drop its guts into "localsub", which can be
 * freely called. (And no, the PANS doesn't require the above behavior,
 * but it *is* desirable.)
 */
static struct pg_tm *
localsub(struct state const *sp, pg_time_t const *timep,
     struct pg_tm *const tmp)
{
  const struct ttinfo *ttisp;
  int     i;
  struct pg_tm *result;
  const pg_time_t t = *timep;

  if (sp == NULL)
    return gmtsub(timep, 0, tmp);
  if ((sp->goback && t < sp->ats[0]) ||
    (sp->goahead && t > sp->ats[sp->timecnt - 1]))
  {
    pg_time_t newt;
    pg_time_t seconds;
    pg_time_t years;

    if (t < sp->ats[0])
      seconds = sp->ats[0] - t;
    else
      seconds = t - sp->ats[sp->timecnt - 1];
    --seconds;

    /*
     * Beware integer overflow, as SECONDS might be close to the maximum
     * pg_time_t.
     */
    years = seconds / SECSPERREPEAT * YEARSPERREPEAT;
    seconds = years * AVGSECSPERYEAR;
    years += YEARSPERREPEAT;
    if (t < sp->ats[0])
      newt = t + seconds + SECSPERREPEAT;
    else
      newt = t - seconds - SECSPERREPEAT;

    if (newt < sp->ats[0] ||
      newt > sp->ats[sp->timecnt - 1])
      return NULL;   /* "cannot happen" */
    result = localsub(sp, &newt, tmp);
    if (result)
    {
#if defined ckd_add && defined ckd_sub
      if (t < sp->ats[0]
        ? ckd_sub(&result->tm_year,
              result->tm_year, years)
        : ckd_add(&result->tm_year,
              result->tm_year, years))
        return NULL;
#else
      int_fast64_t newy;

      newy = result->tm_year;
      if (t < sp->ats[0])
        newy -= years;
      else
        newy += years;
      if (!(INT_MIN <= newy && newy <= INT_MAX))
        return NULL;
      result->tm_year = newy;
#endif
    }
    return result;
  }
  if (sp->timecnt == 0 || t < sp->ats[0])
  {
    i = 0;
  }
  else
  {
    int     lo = 1;
    int     hi = sp->timecnt;

    while (lo < hi)
    {
      int     mid = (lo + hi) >> 1;

      if (t < sp->ats[mid])
        hi = mid;
      else
        lo = mid + 1;
    }
    i = sp->types[lo - 1];
  }
  ttisp = &sp->ttis[i];

  /*
   * To get (wrong) behavior that's compatible with System V Release 2.0
   * you'd replace the statement below with t += ttisp->tt_utoff;
   * timesub(&t, 0, sp, tmp);
   */
  result = timesub(&t, ttisp->tt_utoff, sp, tmp);
  if (result)
  {
    result->tm_isdst = ttisp->tt_isdst;
#ifdef TM_ZONE
    result->TM_ZONE = UNCONST(&sp->chars[ttisp->tt_desigidx]);
#endif
  }
  return result;
}


struct pg_tm *
pg_localtime(const pg_time_t *timep, const pg_tz *tz)
{
  return localsub(&tz->state, timep, &tm);
}


/*
 * gmtsub is to gmtime as localsub is to localtime.
 *
 * PG: except we have a private "struct state" for GMT, so no sp is passed in.
 */

static struct pg_tm *
gmtsub(pg_time_t const *timep,
     int_fast32_t offset, struct pg_tm *tmp)
{
  struct pg_tm *result;

  /* GMT timezone state data is kept here */
  static struct state *gmtptr = NULL;

  if (gmtptr == NULL)
  {
    /* Allocate on first use */
    gmtptr = (struct state *) malloc(sizeof(struct state));
    if (gmtptr == NULL)
      return NULL;   /* errno should be set by malloc */
    gmtload(gmtptr);
  }

  result = timesub(timep, offset, gmtptr, tmp);
#ifdef TM_ZONE

  /*
   * Could get fancy here and deliver something such as "+xx" or "-xx" if
   * offset is non-zero, but this is no time for a treasure hunt.
   */
  tmp->TM_ZONE = UNCONST(offset ? wildabbr
               : gmtptr->chars);
#endif              /* defined TM_ZONE */
  return result;
}

struct pg_tm *
pg_gmtime(const pg_time_t *timep)
{
  return gmtsub(timep, 0, &tm);
}

/*
 * Return the number of leap years through the end of the given year
 * where, to make the math easy, the answer for year zero is defined as zero.
 */

static pg_time_t
leaps_thru_end_of_nonneg(pg_time_t y)
{
  return y / 4 - y / 100 + y / 400;
}

static pg_time_t
leaps_thru_end_of(pg_time_t y)
{
  return (y < 0
      ? -1 - leaps_thru_end_of_nonneg(-1 - y)
      : leaps_thru_end_of_nonneg(y));
}

static struct pg_tm *
timesub(const pg_time_t *timep, int_fast32_t offset,
    const struct state *sp, struct pg_tm *tmp)
{
  pg_time_t tdays;
  const int  *ip;
  int_fast32_2s corr;
  int     i;
  int_fast32_t idays,
        rem,
        dayoff,
        dayrem;
  pg_time_t y;

  /*
   * If less than SECSPERMIN, the number of seconds since the most recent
   * positive leap second; otherwise, do not add 1 to localtime tm_sec
   * because of leap seconds.
   */
  pg_time_t secs_since_posleap = SECSPERMIN;

  corr = 0;
  i = sp ? leapcount(sp) : 0;
  while (--i >= 0)
  {
    struct lsinfo ls = lsinfo(sp, i);

    if (ls.ls_trans <= *timep)
    {
      corr = ls.ls_corr;
      if ((i == 0 ? 0 : lsinfo(sp, i - 1).ls_corr) < corr)
        secs_since_posleap = *timep - ls.ls_trans;
      break;
    }
  }

  /*
   * Calculate the year, avoiding integer overflow even if pg_time_t is
   * unsigned.
   */
  tdays = *timep / SECSPERDAY;
  rem = *timep % SECSPERDAY;
  rem += offset % SECSPERDAY - corr % SECSPERDAY + 3 * SECSPERDAY;
  dayoff = offset / SECSPERDAY - corr / SECSPERDAY + rem / SECSPERDAY - 3;
  rem %= SECSPERDAY;

  /*
   * y = (EPOCH_YEAR + floor((tdays + dayoff) / DAYSPERREPEAT) *
   * YEARSPERREPEAT), sans overflow.  But calculate against 1570 (EPOCH_YEAR
   * - YEARSPERREPEAT) instead of against 1970 so that things work for
   * localtime values before 1970 when pg_time_t is unsigned.
   */
  dayrem = tdays % DAYSPERREPEAT;
  dayrem += dayoff % DAYSPERREPEAT;
  y = (EPOCH_YEAR - YEARSPERREPEAT
     + ((1 + dayoff / DAYSPERREPEAT + dayrem / DAYSPERREPEAT
       - ((dayrem % DAYSPERREPEAT) < 0)
       + tdays / DAYSPERREPEAT)
      * YEARSPERREPEAT));
  /* idays = (tdays + dayoff) mod DAYSPERREPEAT, sans overflow.  */
  idays = tdays % DAYSPERREPEAT;
  idays += dayoff % DAYSPERREPEAT + 2 * DAYSPERREPEAT;
  idays %= DAYSPERREPEAT;
  /* Increase Y and decrease IDAYS until IDAYS is in range for Y.  */
  while (year_lengths[isleap(y)] <= idays)
  {
    int     tdelta = idays / DAYSPERLYEAR;
    int_fast32_t ydelta = tdelta + !tdelta;
    pg_time_t newy = y + ydelta;
    int     leapdays;

    leapdays = leaps_thru_end_of(newy - 1) -
      leaps_thru_end_of(y - 1);
    idays -= ydelta * DAYSPERNYEAR;
    idays -= leapdays;
    y = newy;
  }

#ifdef ckd_add
  if (ckd_add(&tmp->tm_year, y, -TM_YEAR_BASE))
  {
    errno = EOVERFLOW;
    return NULL;
  }
#else
  if (!TYPE_SIGNED(pg_time_t) && y < TM_YEAR_BASE)
  {
    int     signed_y = y;

    tmp->tm_year = signed_y - TM_YEAR_BASE;
  }
  else if ((!TYPE_SIGNED(pg_time_t) || INT_MIN + TM_YEAR_BASE <= y)
       && y - TM_YEAR_BASE <= INT_MAX)
    tmp->tm_year = y - TM_YEAR_BASE;
  else
  {
    errno = EOVERFLOW;
    return NULL;
  }
#endif
  tmp->tm_yday = idays;

  /*
   * The "extra" mods below avoid overflow problems.
   */
  tmp->tm_wday = (TM_WDAY_BASE
          + ((tmp->tm_year % DAYSPERWEEK)
             * (DAYSPERNYEAR % DAYSPERWEEK))
          + leaps_thru_end_of(y - 1)
          - leaps_thru_end_of(TM_YEAR_BASE - 1)
          + idays);
  tmp->tm_wday %= DAYSPERWEEK;
  if (tmp->tm_wday < 0)
    tmp->tm_wday += DAYSPERWEEK;
  tmp->tm_hour = rem / SECSPERHOUR;
  rem %= SECSPERHOUR;
  tmp->tm_min = rem / SECSPERMIN;
  tmp->tm_sec = rem % SECSPERMIN;

  /*
   * Use "... ??:??:60" at the end of the localtime minute containing the
   * second just before the positive leap second.
   */
  tmp->tm_sec += secs_since_posleap <= tmp->tm_sec;

  ip = mon_lengths[isleap(y)];
  for (tmp->tm_mon = 0; idays >= ip[tmp->tm_mon]; ++(tmp->tm_mon))
    idays -= ip[tmp->tm_mon];
  tmp->tm_mday = idays + 1;
  tmp->tm_isdst = 0;
#ifdef TM_GMTOFF
  tmp->TM_GMTOFF = offset;
#endif              /* defined TM_GMTOFF */
  return tmp;
}

/*
 * Adapted from code provided by Robert Elz, who writes:
 *  The "best" way to do mktime I think is based on an idea of Bob
 *  Kridle's (so its said...) from a long time ago.
 *  It does a binary search of the pg_time_t space. Since pg_time_t's are
 *  just 32 bits, its a max of 32 iterations (even at 64 bits it
 *  would still be very reasonable).
 */

#ifndef WRONG
#define WRONG (-1)
#endif              /* !defined WRONG */

/*
 * Normalize logic courtesy Paul Eggert.
 */

static bool
increment_overflow(int *ip, int j)
{
#ifdef ckd_add
  return ckd_add(ip, *ip, j);
#else
  int const i = *ip;

  /*----------
   * If i >= 0 there can only be overflow if i + j > INT_MAX
   * or if j > INT_MAX - i; given i >= 0, INT_MAX - i cannot overflow.
   * If i < 0 there can only be overflow if i + j < INT_MIN
   * or if j < INT_MIN - i; given i < 0, INT_MIN - i cannot overflow.
   *----------
   */
  if ((i >= 0) ? (j > INT_MAX - i) : (j < INT_MIN - i))
    return true;
  *ip += j;
  return false;
#endif
}

static bool
increment_overflow_time(pg_time_t *tp, int_fast32_2s j)
{
#ifdef ckd_add
  return ckd_add(tp, *tp, j);
#else
  /*----------
   * This is like
   * 'if (! (TIME_T_MIN <= *tp + j && *tp + j <= TIME_T_MAX)) ...',
   * except that it does the right thing even if *tp + j would overflow.
   *----------
   */
  if (!(j < 0
      ? (TYPE_SIGNED(pg_time_t) ? TIME_T_MIN - j <= *tp : -1 - j < *tp)
      : *tp <= TIME_T_MAX - j))
    return true;
  *tp += j;
  return false;
#endif
}

static int_fast32_2s
leapcorr(struct state const *sp, pg_time_t t)
{
  int     i;

  i = leapcount(sp);
  while (--i >= 0)
  {
    struct lsinfo ls = lsinfo(sp, i);

    if (ls.ls_trans <= t)
      return ls.ls_corr;
  }
  return 0;
}

/*
 * Postgres-specific functions begin here.
 */

/*
 * Load the definition of the given time zone name into *sp.
 * Return true if successful, false if not.
 * If "canonname" is not NULL, then on success the canonical spelling of
 * given name is stored there (the buffer must be > TZ_STRLEN_MAX bytes!).
 *
 * "GMT" is always interpreted as the gmtload() definition, without attempting
 * to load a definition from the filesystem.  This has a number of benefits:
 * 1. It's guaranteed to succeed, so we don't have the failure mode wherein
 * the bootstrap default timezone setting doesn't work (as could happen if
 * the OS attempts to supply a leap-second-aware version of "GMT").
 * 2. Because we aren't accessing the filesystem, we can safely initialize
 * the "GMT" zone definition before my_exec_path is known.
 * 3. It's quick enough that we don't waste much time when the bootstrap
 * default timezone setting is later overridden from postgresql.conf.
 */
bool
pg_tzload(const char *name, char *canonname, struct state *sp)
{
  if (strcmp(name, "GMT") == 0)
  {
    gmtload(sp);
    /* Use given name as canonical */
    if (canonname)
      strcpy(canonname, name);
  }
  else if (tzload(name, canonname, sp, TZLOAD_TZSTRING) != 0)
  {
    if (name[0] == ':' || !tzparse(name, sp, NULL))
    {
      /* Unknown timezone. Fail our call instead of loading GMT! */
      return false;
    }
    /* For POSIX timezone specs, use given name as canonical */
    if (canonname)
      strcpy(canonname, name);
  }
  return true;
}

/*
 * Find the next DST transition time in the given zone after the given time
 *
 * *timep and *tz are input arguments, the other parameters are output values.
 *
 * When the function result is 1, *boundary is set to the pg_time_t
 * representation of the next DST transition time after *timep,
 * *before_gmtoff and *before_isdst are set to the GMT offset and isdst
 * state prevailing just before that boundary (in particular, the state
 * prevailing at *timep), and *after_gmtoff and *after_isdst are set to
 * the state prevailing just after that boundary.
 *
 * When the function result is 0, there is no known DST transition
 * after *timep, but *before_gmtoff and *before_isdst indicate the GMT
 * offset and isdst state prevailing at *timep.  (This would occur in
 * DST-less time zones, or if a zone has permanently ceased using DST.)
 *
 * A function result of -1 indicates failure (this case does not actually
 * occur in our current implementation).
 */
int
pg_next_dst_boundary(const pg_time_t *timep,
           long int *before_gmtoff,
           int *before_isdst,
           pg_time_t *boundary,
           long int *after_gmtoff,
           int *after_isdst,
           const pg_tz *tz)
{
  const struct state *sp;
  const struct ttinfo *ttisp;
  int     i;
  int     j;
  const pg_time_t t = *timep;

  sp = &tz->state;
  if (sp->timecnt == 0)
  {
    /* non-DST zone, use the defaulttype (now always 0) */
    ttisp = &sp->ttis[0];
    *before_gmtoff = ttisp->tt_utoff;
    *before_isdst = ttisp->tt_isdst;
    return 0;
  }
  if ((sp->goback && t < sp->ats[0]) ||
    (sp->goahead && t > sp->ats[sp->timecnt - 1]))
  {
    /* For values outside the transition table, extrapolate */
    pg_time_t newt = t;
    pg_time_t seconds;
    pg_time_t tcycles;
    int64   icycles;
    int     result;

    if (t < sp->ats[0])
      seconds = sp->ats[0] - t;
    else
      seconds = t - sp->ats[sp->timecnt - 1];
    --seconds;
    tcycles = seconds / YEARSPERREPEAT / AVGSECSPERYEAR;
    ++tcycles;
    icycles = tcycles;
    if (tcycles - icycles >= 1 || icycles - tcycles >= 1)
      return -1;
    seconds = icycles;
    seconds *= YEARSPERREPEAT;
    seconds *= AVGSECSPERYEAR;
    if (t < sp->ats[0])
      newt += seconds;
    else
      newt -= seconds;
    if (newt < sp->ats[0] ||
      newt > sp->ats[sp->timecnt - 1])
      return -1;     /* "cannot happen" */

    result = pg_next_dst_boundary(&newt, before_gmtoff,
                    before_isdst,
                    boundary,
                    after_gmtoff,
                    after_isdst,
                    tz);
    if (t < sp->ats[0])
      *boundary -= seconds;
    else
      *boundary += seconds;
    return result;
  }

  if (t >= sp->ats[sp->timecnt - 1])
  {
    /* No known transition > t, so use last known segment's type */
    i = sp->types[sp->timecnt - 1];
    ttisp = &sp->ttis[i];
    *before_gmtoff = ttisp->tt_utoff;
    *before_isdst = ttisp->tt_isdst;
    return 0;
  }
  if (t < sp->ats[0])
  {
    /* For "before", use the defaulttype (now always 0) */
    ttisp = &sp->ttis[0];
    *before_gmtoff = ttisp->tt_utoff;
    *before_isdst = ttisp->tt_isdst;
    *boundary = sp->ats[0];
    /* And for "after", use the first segment's type */
    i = sp->types[0];
    ttisp = &sp->ttis[i];
    *after_gmtoff = ttisp->tt_utoff;
    *after_isdst = ttisp->tt_isdst;
    return 1;
  }
  /* Else search to find the boundary following t */
  {
    int     lo = 1;
    int     hi = sp->timecnt - 1;

    while (lo < hi)
    {
      int     mid = (lo + hi) >> 1;

      if (t < sp->ats[mid])
        hi = mid;
      else
        lo = mid + 1;
    }
    i = lo;
  }
  j = sp->types[i - 1];
  ttisp = &sp->ttis[j];
  *before_gmtoff = ttisp->tt_utoff;
  *before_isdst = ttisp->tt_isdst;
  *boundary = sp->ats[i];
  j = sp->types[i];
  ttisp = &sp->ttis[j];
  *after_gmtoff = ttisp->tt_utoff;
  *after_isdst = ttisp->tt_isdst;
  return 1;
}

/*
 * Identify a timezone abbreviation's meaning in the given zone
 *
 * Determine the GMT offset and DST flag associated with the abbreviation.
 * This is generally used only when the abbreviation has actually changed
 * meaning over time; therefore, we also take a UTC cutoff time, and return
 * the meaning in use at or most recently before that time, or the meaning
 * in first use after that time if the abbrev was never used before that.
 *
 * On success, returns true and sets *gmtoff and *isdst.  If the abbreviation
 * was never used at all in this zone, returns false.
 *
 * Note: abbrev is matched case-sensitively; it should be all-upper-case.
 */
bool
pg_interpret_timezone_abbrev(const char *abbrev,
               const pg_time_t *timep,
               long int *gmtoff,
               int *isdst,
               const pg_tz *tz)
{
  const struct state *sp;
  const char *abbrs;
  const struct ttinfo *ttisp;
  int     abbrind;
  int     cutoff;
  int     i;
  const pg_time_t t = *timep;

  sp = &tz->state;

  /*
   * Locate the abbreviation in the zone's abbreviation list.  We assume
   * there are not duplicates in the list.
   */
  abbrs = sp->chars;
  abbrind = 0;
  while (abbrind < sp->charcnt)
  {
    if (strcmp(abbrev, abbrs + abbrind) == 0)
      break;
    while (abbrs[abbrind] != '\0')
      abbrind++;
    abbrind++;
  }
  if (abbrind >= sp->charcnt)
    return false;     /* not there! */

  /*
   * Unlike pg_next_dst_boundary, we needn't sweat about extrapolation
   * (goback/goahead zones).  Finding the newest or oldest meaning of the
   * abbreviation should get us what we want, since extrapolation would just
   * be repeating the newest or oldest meanings.
   *
   * Use binary search to locate the first transition > cutoff time.  (Note
   * that sp->timecnt could be zero, in which case this loop does nothing
   * and only the defaulttype entry will be checked.)
   */
  {
    int     lo = 0;
    int     hi = sp->timecnt;

    while (lo < hi)
    {
      int     mid = (lo + hi) >> 1;

      if (t < sp->ats[mid])
        hi = mid;
      else
        lo = mid + 1;
    }
    cutoff = lo;
  }

  /*
   * Scan backwards to find the latest interval using the given abbrev
   * before the cutoff time.
   */
  for (i = cutoff - 1; i >= 0; i--)
  {
    ttisp = &sp->ttis[sp->types[i]];
    if (ttisp->tt_desigidx == abbrind)
    {
      *gmtoff = ttisp->tt_utoff;
      *isdst = ttisp->tt_isdst;
      return true;
    }
  }

  /*
   * Not found yet; check the defaulttype, which is notionally the era
   * before any of the entries in sp->types[].
   */
  ttisp = &sp->ttis[0];
  if (ttisp->tt_desigidx == abbrind)
  {
    *gmtoff = ttisp->tt_utoff;
    *isdst = ttisp->tt_isdst;
    return true;
  }

  /*
   * Not there, so scan forwards to find the first one after the cutoff.
   */
  for (i = cutoff; i < sp->timecnt; i++)
  {
    ttisp = &sp->ttis[sp->types[i]];
    if (ttisp->tt_desigidx == abbrind)
    {
      *gmtoff = ttisp->tt_utoff;
      *isdst = ttisp->tt_isdst;
      return true;
    }
  }

  return false;       /* hm, not actually used in any interval? */
}

/*
 * Detect whether a timezone abbreviation is defined within the given zone.
 *
 * This is similar to pg_interpret_timezone_abbrev() but is not concerned
 * with a specific point in time.  We want to know if the abbreviation is
 * known at all, and if so whether it has one meaning or several.
 *
 * Returns true if the abbreviation is known, false if not.
 * If the abbreviation is known and has a single meaning (only one value
 * of gmtoff/isdst), sets *isfixed = true and sets *gmtoff and *isdst.
 * If there are multiple meanings, sets *isfixed = false.
 *
 * Note: abbrev is matched case-sensitively; it should be all-upper-case.
 */
bool
pg_timezone_abbrev_is_known(const char *abbrev,
              bool *isfixed,
              long int *gmtoff,
              int *isdst,
              const pg_tz *tz)
{
  bool    result = false;
  const struct state *sp = &tz->state;
  const char *abbrs;
  int     abbrind;

  /*
   * Locate the abbreviation in the zone's abbreviation list.  We assume
   * there are not duplicates in the list.
   */
  abbrs = sp->chars;
  abbrind = 0;
  while (abbrind < sp->charcnt)
  {
    if (strcmp(abbrev, abbrs + abbrind) == 0)
      break;
    while (abbrs[abbrind] != '\0')
      abbrind++;
    abbrind++;
  }
  if (abbrind >= sp->charcnt)
    return false;     /* definitely not there */

  /*
   * Scan the ttinfo array to find uses of the abbreviation.
   */
  for (int i = 0; i < sp->typecnt; i++)
  {
    const struct ttinfo *ttisp = &sp->ttis[i];

    if (ttisp->tt_desigidx == abbrind)
    {
      if (!result)
      {
        /* First usage */
        *isfixed = true; /* for the moment */
        *gmtoff = ttisp->tt_utoff;
        *isdst = ttisp->tt_isdst;
        result = true;
      }
      else
      {
        /* Second or later usage, does it match? */
        if (*gmtoff != ttisp->tt_utoff ||
          *isdst != ttisp->tt_isdst)
        {
          *isfixed = false;
          break;    /* no point in looking further */
        }
      }
    }
  }

  return result;
}

/*
 * Iteratively fetch all the abbreviations used in the given time zone.
 *
 * *indx is a state counter that the caller must initialize to zero
 * before the first call, and not touch between calls.
 *
 * Returns the next known abbreviation, or NULL if there are no more.
 *
 * Note: the caller typically applies pg_interpret_timezone_abbrev()
 * to each result.  While that nominally results in O(N^2) time spent
 * searching the sp->chars[] array, we don't expect any zone to have
 * enough abbreviations to make that meaningful.
 */
const char *
pg_get_next_timezone_abbrev(int *indx,
              const pg_tz *tz)
{
  const char *result;
  const struct state *sp = &tz->state;
  const char *abbrs;
  int     abbrind;

  /* If we're still in range, the result is the current abbrev. */
  abbrs = sp->chars;
  abbrind = *indx;
  if (abbrind < 0 || abbrind >= sp->charcnt)
    return NULL;
  result = abbrs + abbrind;

  /* Advance *indx past this abbrev and its trailing null. */
  while (abbrs[abbrind] != '\0')
    abbrind++;
  abbrind++;
  *indx = abbrind;

  return result;
}

/*
 * If the given timezone uses only one GMT offset, store that offset
 * into *gmtoff and return true, else return false.
 */
bool
pg_get_timezone_offset(const pg_tz *tz, long int *gmtoff)
{
  /*
   * The zone could have more than one ttinfo, if it's historically used
   * more than one abbreviation.  We return true as long as they all have
   * the same gmtoff.
   */
  const struct state *sp;
  int     i;

  sp = &tz->state;
  for (i = 1; i < sp->typecnt; i++)
  {
    if (sp->ttis[i].tt_utoff != sp->ttis[0].tt_utoff)
      return false;
  }
  *gmtoff = sp->ttis[0].tt_utoff;
  return true;
}

/*
 * Return the name of the current timezone
 */
const char *
pg_get_timezone_name(pg_tz *tz)
{
  if (tz)
    return tz->TZname;
  return NULL;
}

/*
 * Check whether timezone is acceptable.
 *
 * What we are doing here is checking for leap-second-aware timekeeping.
 * We need to reject such TZ settings because they'll wreak havoc with our
 * date/time arithmetic.
 */
bool
pg_tz_acceptable(pg_tz *tz)
{
  struct pg_tm *tt;
  pg_time_t time2000;

  /*
   * To detect leap-second timekeeping, run pg_localtime for what should be
   * GMT midnight, 2000-01-01.  Insist that the tm_sec value be zero; any
   * other result has to be due to leap seconds.
   */
  time2000 = (POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY;
  tt = pg_localtime(&time2000, tz);
  if (!tt || tt->tm_sec != 0)
    return false;

  return true;
}

Coverage Report

Created: 2026-08-14 06:37