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typedef ... time_t

This is the system defined time type which is usually the number of
seconds since midnight beginning 1 January 1970.


typedef ... eday_t

Number of days since the Julian Epoch, which is:
In the Gregorian proleptic calendar:  Monday 24 November 4714 BC
In the Julian proleptic calendar:     Monday 1 January 4713 BC


typedef ... etime_t

Number of microseconds since midnight beginning the Julian Epoch.


typedef ... time64_t

Same as time_t except is always at least 64 bits in size.


typedef ... timems_t

Number of milliseconds since the same epoch as time_t.


typedef ... timeus_t

Number of microseconds since the same epoch as time_t.


typedef ... timens_t

Number of nanoseconds since the same epoch as time_t.


typedef double JD;
typedef long double LJD;

The Julian Date, defined as a floating point type value with an epoch
of noon on the day of the Julian Epoch.


typedef ... ecal_t

This is a struct that contains these members:
	type		flag indicating whether Gregorian or Julian
	isleap		true if this is a leap year
	year		year as an absolute value, e.g. 2000
	month		month 1..12
	yday		day of year 0..365
	mday		day of month 1..31
	wday		day of week 1..7
	week		week of year 0..53
	hour		hour of day 0..23
	min		minute of hours 0..59
	sec		second of minute 0..59
	nsec		nanosecond of minute 0..999999999


typedef ... xday_t

Number of days since 18 Sept 763 in the Gregorian proleptic calendar.
The usefulness of this value is that from 16 Nov 1858 to 14 Aug 3501,
the value is in the range 400000 to 999999 which allows it to be used
in places where dates are stored as six characters, and allowing them
to be distinguished from the common MMDDYY format by testing the first
character to see if it is in the range '4' to '9'.  Or the test can be
done by testing only if the first character is '4' which limits the
range to 30 August 2132.  This scheme was invented by Bob Bemer.

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