src/include/datatype/timestamp.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * timestamp.h
   4  *        Timestamp and Interval typedefs and related macros.
   5  *
   6  * Note: this file must be includable in both frontend and backend contexts.
   7  *
   8  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
   9  * Portions Copyright (c) 1994, Regents of the University of California
  10  *
  11  * src/include/datatype/timestamp.h
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 #ifndef DATATYPE_TIMESTAMP_H
  16 #define DATATYPE_TIMESTAMP_H
  17
  18 /*
  19  * Timestamp represents absolute time.
  20  *
  21  * Interval represents delta time. Keep track of months (and years), days,
  22  * and hours/minutes/seconds separately since the elapsed time spanned is
  23  * unknown until instantiated relative to an absolute time.
  24  *
  25  * Note that Postgres uses "time interval" to mean a bounded interval,
  26  * consisting of a beginning and ending time, not a time span - thomas 97/03/20
  27  *
  28  * Timestamps, as well as the h/m/s fields of intervals, are stored as
  29  * int64 values with units of microseconds.  (Once upon a time they were
  30  * double values with units of seconds.)
  31  *
  32  * TimeOffset and fsec_t are convenience typedefs for temporary variables.
  33  * Do not use fsec_t in values stored on-disk.
  34  * Also, fsec_t is only meant for *fractional* seconds; beware of overflow
  35  * if the value you need to store could be many seconds.
  36  */
  37
  38 typedef int64 Timestamp;
  39 typedef int64 TimestampTz;
  40 typedef int64 TimeOffset;
  41 typedef int32 fsec_t;                   /* fractional seconds (in microseconds) */
  42
  43
  44 /*
  45  * Storage format for type interval.
  46  */
  47 typedef struct
  48 {
  49         TimeOffset      time;                   /* all time units other than days, months and
  50                                                                  * years */
  51         int32           day;                    /* days, after time for alignment */
  52         int32           month;                  /* months and years, after time for alignment */
  53 } Interval;
  54
  55 /*
  56  * Data structure representing a broken-down interval.
  57  *
  58  * For historical reasons, this is modeled on struct pg_tm for timestamps.
  59  * Unlike the situation for timestamps, there's no magic interpretation
  60  * needed for months or years: they're just zero or not.  Note that fields
  61  * can be negative; however, because of the divisions done while converting
  62  * from struct Interval, only tm_mday could be INT_MIN.  This is important
  63  * because we may need to negate the values in some code paths.
  64  */
  65 struct pg_itm
  66 {
  67         int                     tm_usec;
  68         int                     tm_sec;
  69         int                     tm_min;
  70         int64           tm_hour;                /* needs to be wide */
  71         int                     tm_mday;
  72         int                     tm_mon;
  73         int                     tm_year;
  74 };
  75
  76 /*
  77  * Data structure for decoding intervals.  We could just use struct pg_itm,
  78  * but then the requirement for tm_usec to be 64 bits would propagate to
  79  * places where it's not really needed.  Also, omitting the fields that
  80  * aren't used during decoding seems like a good error-prevention measure.
  81  */
  82 struct pg_itm_in
  83 {
  84         int64           tm_usec;                /* needs to be wide */
  85         int                     tm_mday;
  86         int                     tm_mon;
  87         int                     tm_year;
  88 };
  89
  90
  91 /* Limits on the "precision" option (typmod) for these data types */
  92 #define MAX_TIMESTAMP_PRECISION 6
  93 #define MAX_INTERVAL_PRECISION 6
  94
  95 /*
  96  *      Round off to MAX_TIMESTAMP_PRECISION decimal places.
  97  *      Note: this is also used for rounding off intervals.
  98  */
  99 #define TS_PREC_INV 1000000.0
 100 #define TSROUND(j) (rint(((double) (j)) * TS_PREC_INV) / TS_PREC_INV)
 101
 102
 103 /*
 104  * Assorted constants for datetime-related calculations
 105  */
 106
 107 #define DAYS_PER_YEAR   365.25  /* assumes leap year every four years */
 108 #define MONTHS_PER_YEAR 12
 109 /*
 110  *      DAYS_PER_MONTH is very imprecise.  The more accurate value is
 111  *      365.2425/12 = 30.436875, or '30 days 10:29:06'.  Right now we only
 112  *      return an integral number of days, but someday perhaps we should
 113  *      also return a 'time' value to be used as well.  ISO 8601 suggests
 114  *      30 days.
 115  */
 116 #define DAYS_PER_MONTH  30              /* assumes exactly 30 days per month */
 117 #define HOURS_PER_DAY   24              /* assume no daylight savings time changes */
 118
 119 /*
 120  *      This doesn't adjust for uneven daylight savings time intervals or leap
 121  *      seconds, and it crudely estimates leap years.  A more accurate value
 122  *      for days per years is 365.2422.
 123  */
 124 #define SECS_PER_YEAR   (36525 * 864)   /* avoid floating-point computation */
 125 #define SECS_PER_DAY    86400
 126 #define SECS_PER_HOUR   3600
 127 #define SECS_PER_MINUTE 60
 128 #define MINS_PER_HOUR   60
 129
 130 #define USECS_PER_DAY   INT64CONST(86400000000)
 131 #define USECS_PER_HOUR  INT64CONST(3600000000)
 132 #define USECS_PER_MINUTE INT64CONST(60000000)
 133 #define USECS_PER_SEC   INT64CONST(1000000)
 134
 135 /*
 136  * We allow numeric timezone offsets up to 15:59:59 either way from Greenwich.
 137  * Currently, the record holders for wackiest offsets in actual use are zones
 138  * Asia/Manila, at -15:56:00 until 1844, and America/Metlakatla, at +15:13:42
 139  * until 1867.  If we were to reject such values we would fail to dump and
 140  * restore old timestamptz values with these zone settings.
 141  */
 142 #define MAX_TZDISP_HOUR         15      /* maximum allowed hour part */
 143 #define TZDISP_LIMIT            ((MAX_TZDISP_HOUR + 1) * SECS_PER_HOUR)
 144
 145 /*
 146  * We reserve the minimum and maximum integer values to represent
 147  * timestamp (or timestamptz) -infinity and +infinity.
 148  */
 149 #define TIMESTAMP_MINUS_INFINITY        PG_INT64_MIN
 150 #define TIMESTAMP_INFINITY      PG_INT64_MAX
 151
 152 /*
 153  * Historically these alias for infinity have been used.
 154  */
 155 #define DT_NOBEGIN              TIMESTAMP_MINUS_INFINITY
 156 #define DT_NOEND                TIMESTAMP_INFINITY
 157
 158 #define TIMESTAMP_NOBEGIN(j)    \
 159         do {(j) = DT_NOBEGIN;} while (0)
 160
 161 #define TIMESTAMP_IS_NOBEGIN(j) ((j) == DT_NOBEGIN)
 162
 163 #define TIMESTAMP_NOEND(j)              \
 164         do {(j) = DT_NOEND;} while (0)
 165
 166 #define TIMESTAMP_IS_NOEND(j)   ((j) == DT_NOEND)
 167
 168 #define TIMESTAMP_NOT_FINITE(j) (TIMESTAMP_IS_NOBEGIN(j) || TIMESTAMP_IS_NOEND(j))
 169
 170
 171 /*
 172  * Julian date support.
 173  *
 174  * date2j() and j2date() nominally handle the Julian date range 0..INT_MAX,
 175  * or 4714-11-24 BC to 5874898-06-03 AD.  In practice, date2j() will work and
 176  * give correct negative Julian dates for dates before 4714-11-24 BC as well.
 177  * We rely on it to do so back to 4714-11-01 BC.  Allowing at least one day's
 178  * slop is necessary so that timestamp rotation doesn't produce dates that
 179  * would be rejected on input.  For example, '4714-11-24 00:00 GMT BC' is a
 180  * legal timestamptz value, but in zones east of Greenwich it would print as
 181  * sometime in the afternoon of 4714-11-23 BC; if we couldn't process such a
 182  * date we'd have a dump/reload failure.  So the idea is for IS_VALID_JULIAN
 183  * to accept a slightly wider range of dates than we really support, and
 184  * then we apply the exact checks in IS_VALID_DATE or IS_VALID_TIMESTAMP,
 185  * after timezone rotation if any.  To save a few cycles, we can make
 186  * IS_VALID_JULIAN check only to the month boundary, since its exact cutoffs
 187  * are not very critical in this scheme.
 188  *
 189  * It is correct that JULIAN_MINYEAR is -4713, not -4714; it is defined to
 190  * allow easy comparison to tm_year values, in which we follow the convention
 191  * that tm_year <= 0 represents abs(tm_year)+1 BC.
 192  */
 193
 194 #define JULIAN_MINYEAR (-4713)
 195 #define JULIAN_MINMONTH (11)
 196 #define JULIAN_MINDAY (24)
 197 #define JULIAN_MAXYEAR (5874898)
 198 #define JULIAN_MAXMONTH (6)
 199 #define JULIAN_MAXDAY (3)
 200
 201 #define IS_VALID_JULIAN(y,m,d) \
 202         (((y) > JULIAN_MINYEAR || \
 203           ((y) == JULIAN_MINYEAR && ((m) >= JULIAN_MINMONTH))) && \
 204          ((y) < JULIAN_MAXYEAR || \
 205           ((y) == JULIAN_MAXYEAR && ((m) < JULIAN_MAXMONTH))))
 206
 207 /* Julian-date equivalents of Day 0 in Unix and Postgres reckoning */
 208 #define UNIX_EPOCH_JDATE                2440588 /* == date2j(1970, 1, 1) */
 209 #define POSTGRES_EPOCH_JDATE    2451545 /* == date2j(2000, 1, 1) */
 210
 211 /*
 212  * Range limits for dates and timestamps.
 213  *
 214  * We have traditionally allowed Julian day zero as a valid datetime value,
 215  * so that is the lower bound for both dates and timestamps.
 216  *
 217  * The upper limit for dates is 5874897-12-31, which is a bit less than what
 218  * the Julian-date code can allow.  For timestamps, the upper limit is
 219  * 294276-12-31.  The int64 overflow limit would be a few days later; again,
 220  * leaving some slop avoids worries about corner-case overflow, and provides
 221  * a simpler user-visible definition.
 222  */
 223
 224 /* First allowed date, and first disallowed date, in Julian-date form */
 225 #define DATETIME_MIN_JULIAN (0)
 226 #define DATE_END_JULIAN (2147483494)    /* == date2j(JULIAN_MAXYEAR, 1, 1) */
 227 #define TIMESTAMP_END_JULIAN (109203528)        /* == date2j(294277, 1, 1) */
 228
 229 /* Timestamp limits */
 230 #define MIN_TIMESTAMP   INT64CONST(-211813488000000000)
 231 /* == (DATETIME_MIN_JULIAN - POSTGRES_EPOCH_JDATE) * USECS_PER_DAY */
 232 #define END_TIMESTAMP   INT64CONST(9223371331200000000)
 233 /* == (TIMESTAMP_END_JULIAN - POSTGRES_EPOCH_JDATE) * USECS_PER_DAY */
 234
 235 /* Range-check a date (given in Postgres, not Julian, numbering) */
 236 #define IS_VALID_DATE(d) \
 237         ((DATETIME_MIN_JULIAN - POSTGRES_EPOCH_JDATE) <= (d) && \
 238          (d) < (DATE_END_JULIAN - POSTGRES_EPOCH_JDATE))
 239
 240 /* Range-check a timestamp */
 241 #define IS_VALID_TIMESTAMP(t)  (MIN_TIMESTAMP <= (t) && (t) < END_TIMESTAMP)
 242
 243 #endif                                                  /* DATATYPE_TIMESTAMP_H */