DTJulianDateToQwordDate
Converts a Julian Date number to a QWORD value containing date information. Uses CCYYMMDD DateTime Format
DTJulianDateToQwordDate PROTO JulianDate:QWORD
Parameters
JulianDate- AQWORDvalue containing the Julian date integer to convert to aQWORDformat inRAX
Returns
On return RAX will contain the date information in the following format:
RAX Register Bits:
+--------------------------------------------------+------------------------+------------+-----------+ | DWORD | WORD | BYTE | BYTE | +--------------------------------------------------+------------------------+------------+-----------+ | Bits 63-32 | Bits 31-16 | Bits 15-8 | Bits 7-0 | +--------------------------------------------------+------------------------+------------+-----------+ | Not used - Not applicable | Century Year | Month | Day | +--------------------------------------------------+------------------------+------------+-----------+ | N/A | CCCCYY | MM | DD | +--------------------------------------------------+------------------------+------------+-----------+
Notes
The Julian Day Count is a uniform count of days from a remote epoch in the past (-4712 January 1, 12 hours Greenwich Mean Time (Julian proleptic Calendar) = 4713 BCE January 1, 12 hours GMT (Julian proleptic Calendar) At this instant, the Julian Day Number is 0.
The Julian Day Count has nothing to do with the Julian Calendar introduced by Julius Caesar. It is named for Julius Scaliger, the father of Josephus Justus Scaliger, who invented the concept. It can also be thought of as a logical follow-on to the old Egyptian civil calendar, which also used years of constant lengths.
Scaliger chose the particular date in the remote past because it was before recorded history and because in that year, three important cycles coincided with their first year of the cycle: The 19-year Metonic Cycle, the 15-year Indiction Cycle (a Roman Taxation Cycle) and the 28-year Solar Cycle (the length of time for the old Julian Calendar to repeat exactly).
Example
.data
Day db 0
Month db 0
CentYear dw 0
.code
Invoke DTJulianDateToQwordDate, 2299161 ; Gregorian date of this Julian Date value is 1582 October 15
mov rdx, rax
mov Month, ah
mov Day, al
shr rax, 16 ; move year info into lower word of eax
mov CentYear, ax
; 1582 October 15 - CentYear now contains 1582, Month contains 10, Day contains 15
See Also