timestamp.h

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/*-------------------------------------------------------------------------
 *
 * timestamp.h
 *    Timestamp and Interval typedefs and related macros.
 *
 * Note: this file must be includable in both frontend and backend contexts.
 *
 * Portions Copyright (c) 1996-2013, 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

#include <math.h>
#include <limits.h>
#include <float.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
 *
 * We have two implementations, one that uses int64 values with units of
 * microseconds, and one that uses double values with units of seconds.
 *
 * TimeOffset and fsec_t are convenience typedefs for temporary variables
 * that are of different types in the two cases.  Do not use fsec_t in values
 * stored on-disk, since it is not the same size in both implementations.
 * Also, fsec_t is only meant for *fractional* seconds; beware of overflow
 * if the value you need to store could be many seconds.
 */

#ifdef HAVE_INT64_TIMESTAMP

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

typedef double Timestamp;
typedef double TimestampTz;
typedef double TimeOffset;
typedef double fsec_t;          /* fractional seconds (in seconds) */
#endif

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;


#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
 */
#ifdef HAVE_INT64_TIMESTAMP
#define DT_NOBEGIN      (-INT64CONST(0x7fffffffffffffff) - 1)
#define DT_NOEND        (INT64CONST(0x7fffffffffffffff))
#else                           /* !HAVE_INT64_TIMESTAMP */
#ifdef HUGE_VAL
#define DT_NOBEGIN      (-HUGE_VAL)
#define DT_NOEND        (HUGE_VAL)
#else
#define DT_NOBEGIN      (-DBL_MAX)
#define DT_NOEND        (DBL_MAX)
#endif
#endif   /* HAVE_INT64_TIMESTAMP */

#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.
 *
 * IS_VALID_JULIAN checks the minimum date exactly, but is a bit sloppy
 * about the maximum, since it's far enough out to not be especially
 * interesting.
 */

#define JULIAN_MINYEAR (-4713)
#define JULIAN_MINMONTH (11)
#define JULIAN_MINDAY (24)
#define JULIAN_MAXYEAR (5874898)

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

#define JULIAN_MAX (2147483494) /* == date2j(JULIAN_MAXYEAR, 1, 1) */

/* 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) */

#endif   /* DATATYPE_TIMESTAMP_H */