src/include/datatype/timestamp.h

/*-------------------------------------------------------------------------
 *
 * timestamp.h
 *	  Timestamp and Interval typedefs and related macros.
 *
 * Note: this file must be includable in both frontend and backend contexts.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/datatype/timestamp.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef DATATYPE_TIMESTAMP_H
#define DATATYPE_TIMESTAMP_H

/*
 * Timestamp represents absolute time.
 *
 * Interval represents delta time. Keep track of months (and years), days,
 * and hours/minutes/seconds separately since the elapsed time spanned is
 * unknown until instantiated relative to an absolute time.
 *
 * Note that Postgres uses "time interval" to mean a bounded interval,
 * consisting of a beginning and ending time, not a time span - thomas 97/03/20
 *
 * Timestamps, as well as the h/m/s fields of intervals, are stored as
 * int64 values with units of microseconds.  (Once upon a time they were
 * double values with units of seconds.)
 *
 * TimeOffset and fsec_t are convenience typedefs for temporary variables.
 * Do not use fsec_t in values stored on-disk.
 * Also, fsec_t is only meant for *fractional* seconds; beware of overflow
 * if the value you need to store could be many seconds.
 */

typedef int64 Timestamp;
typedef int64 TimestampTz;
typedef int64 TimeOffset;
typedef int32 fsec_t;			/* fractional seconds (in microseconds) */

typedef struct
{
	TimeOffset	time;			/* all time units other than days, months and
								 * years */
	int32		day;			/* days, after time for alignment */
	int32		month;			/* months and years, after time for alignment */
} Interval;


/* Limits on the "precision" option (typmod) for these data types */
#define MAX_TIMESTAMP_PRECISION 6
#define MAX_INTERVAL_PRECISION 6

/*
 *	Round off to MAX_TIMESTAMP_PRECISION decimal places.
 *	Note: this is also used for rounding off intervals.
 */
#define TS_PREC_INV 1000000.0
#define TSROUND(j) (rint(((double) (j)) * TS_PREC_INV) / TS_PREC_INV)


/*
 * Assorted constants for datetime-related calculations
 */

#define DAYS_PER_YEAR	365.25	/* assumes leap year every four years */
#define MONTHS_PER_YEAR 12
/*
 *	DAYS_PER_MONTH is very imprecise.  The more accurate value is
 *	365.2425/12 = 30.436875, or '30 days 10:29:06'.  Right now we only
 *	return an integral number of days, but someday perhaps we should
 *	also return a 'time' value to be used as well.  ISO 8601 suggests
 *	30 days.
 */
#define DAYS_PER_MONTH	30		/* assumes exactly 30 days per month */
#define HOURS_PER_DAY	24		/* assume no daylight savings time changes */

/*
 *	This doesn't adjust for uneven daylight savings time intervals or leap
 *	seconds, and it crudely estimates leap years.  A more accurate value
 *	for days per years is 365.2422.
 */
#define SECS_PER_YEAR	(36525 * 864)	/* avoid floating-point computation */
#define SECS_PER_DAY	86400
#define SECS_PER_HOUR	3600
#define SECS_PER_MINUTE 60
#define MINS_PER_HOUR	60

#define USECS_PER_DAY	INT64CONST(86400000000)
#define USECS_PER_HOUR	INT64CONST(3600000000)
#define USECS_PER_MINUTE INT64CONST(60000000)
#define USECS_PER_SEC	INT64CONST(1000000)

/*
 * We allow numeric timezone offsets up to 15:59:59 either way from Greenwich.
 * Currently, the record holders for wackiest offsets in actual use are zones
 * Asia/Manila, at -15:56:00 until 1844, and America/Metlakatla, at +15:13:42
 * until 1867.  If we were to reject such values we would fail to dump and
 * restore old timestamptz values with these zone settings.
 */
#define MAX_TZDISP_HOUR		15	/* maximum allowed hour part */
#define TZDISP_LIMIT		((MAX_TZDISP_HOUR + 1) * SECS_PER_HOUR)

/*
 * DT_NOBEGIN represents timestamp -infinity; DT_NOEND represents +infinity
 */
#define DT_NOBEGIN		PG_INT64_MIN
#define DT_NOEND		PG_INT64_MAX

#define TIMESTAMP_NOBEGIN(j)	\
	do {(j) = DT_NOBEGIN;} while (0)

#define TIMESTAMP_IS_NOBEGIN(j) ((j) == DT_NOBEGIN)

#define TIMESTAMP_NOEND(j)		\
	do {(j) = DT_NOEND;} while (0)

#define TIMESTAMP_IS_NOEND(j)	((j) == DT_NOEND)

#define TIMESTAMP_NOT_FINITE(j) (TIMESTAMP_IS_NOBEGIN(j) || TIMESTAMP_IS_NOEND(j))


/*
 * Julian date support.
 *
 * date2j() and j2date() nominally handle the Julian date range 0..INT_MAX,
 * or 4714-11-24 BC to 5874898-06-03 AD.  In practice, date2j() will work and
 * give correct negative Julian dates for dates before 4714-11-24 BC as well.
 * We rely on it to do so back to 4714-11-01 BC.  Allowing at least one day's
 * slop is necessary so that timestamp rotation doesn't produce dates that
 * would be rejected on input.  For example, '4714-11-24 00:00 GMT BC' is a
 * legal timestamptz value, but in zones east of Greenwich it would print as
 * sometime in the afternoon of 4714-11-23 BC; if we couldn't process such a
 * date we'd have a dump/reload failure.  So the idea is for IS_VALID_JULIAN
 * to accept a slightly wider range of dates than we really support, and
 * then we apply the exact checks in IS_VALID_DATE or IS_VALID_TIMESTAMP,
 * after timezone rotation if any.  To save a few cycles, we can make
 * IS_VALID_JULIAN check only to the month boundary, since its exact cutoffs
 * are not very critical in this scheme.
 *
 * It is correct that JULIAN_MINYEAR is -4713, not -4714; it is defined to
 * allow easy comparison to tm_year values, in which we follow the convention
 * that tm_year <= 0 represents abs(tm_year)+1 BC.
 */

#define JULIAN_MINYEAR (-4713)
#define JULIAN_MINMONTH (11)
#define JULIAN_MINDAY (24)
#define JULIAN_MAXYEAR (5874898)
#define JULIAN_MAXMONTH (6)
#define JULIAN_MAXDAY (3)

#define IS_VALID_JULIAN(y,m,d) \
	(((y) > JULIAN_MINYEAR || \
	  ((y) == JULIAN_MINYEAR && ((m) >= JULIAN_MINMONTH))) && \
	 ((y) < JULIAN_MAXYEAR || \
	  ((y) == JULIAN_MAXYEAR && ((m) < JULIAN_MAXMONTH))))

/* Julian-date equivalents of Day 0 in Unix and Postgres reckoning */
#define UNIX_EPOCH_JDATE		2440588 /* == date2j(1970, 1, 1) */
#define POSTGRES_EPOCH_JDATE	2451545 /* == date2j(2000, 1, 1) */

/*
 * Range limits for dates and timestamps.
 *
 * We have traditionally allowed Julian day zero as a valid datetime value,
 * so that is the lower bound for both dates and timestamps.
 *
 * The upper limit for dates is 5874897-12-31, which is a bit less than what
 * the Julian-date code can allow.  For timestamps, the upper limit is
 * 294276-12-31.  The int64 overflow limit would be a few days later; again,
 * leaving some slop avoids worries about corner-case overflow, and provides
 * a simpler user-visible definition.
 */

/* First allowed date, and first disallowed date, in Julian-date form */
#define DATETIME_MIN_JULIAN (0)
#define DATE_END_JULIAN (2147483494)	/* == date2j(JULIAN_MAXYEAR, 1, 1) */
#define TIMESTAMP_END_JULIAN (109203528)	/* == date2j(294277, 1, 1) */

/* Timestamp limits */
#define MIN_TIMESTAMP	INT64CONST(-211813488000000000)
/* == (DATETIME_MIN_JULIAN - POSTGRES_EPOCH_JDATE) * USECS_PER_DAY */
#define END_TIMESTAMP	INT64CONST(9223371331200000000)
/* == (TIMESTAMP_END_JULIAN - POSTGRES_EPOCH_JDATE) * USECS_PER_DAY */

/* Range-check a date (given in Postgres, not Julian, numbering) */
#define IS_VALID_DATE(d) \
	((DATETIME_MIN_JULIAN - POSTGRES_EPOCH_JDATE) <= (d) && \
	 (d) < (DATE_END_JULIAN - POSTGRES_EPOCH_JDATE))

/* Range-check a timestamp */
#define IS_VALID_TIMESTAMP(t)  (MIN_TIMESTAMP <= (t) && (t) < END_TIMESTAMP)

#endif							/* DATATYPE_TIMESTAMP_H */