Julian dates

[Jo ë l Guillod]

For interested parties, here are the 3 base handler/functions I use for
Julian daycount. I have a more elaborated library and could publish it if
anyone is interested (e.g. converting from/to short system date or MySQL
date formats,...).


/** date.julian return the julian count, i.e. days since 24.11.-4713
@param d is the day
@param m is the month
@param y is the year
@returns is the julian count
*/
function date.julian d,m,y
  return (1461*(y+4800+(m-14) div 12)) div 4+(367*(m-2-12*((m-14) div 12)))
div 12-(3*((y+4900.0+(m-14) div 12) div 100)) div 4+d-32075
end date.julian

/** date.julian2DMY aJulian, at d, at m, at y
@purpose Set the day, month year according to the julian date aJulian.
*/
on date.julian2DMY aJulian, at d, at m, at y
  put aJulian + 68569.0 into l
  put ( 4 * l )  div  146097.0 into n
  put l - ( 146097.0 * n + 3 )  div  4 into l
  put ( 4000.0 * ( l + 1 ) )  div  1461001.0  into i -- (that's 1,461,001)
  put l - ( 1461 * i )  div  4 + 31 into l
  put ( 80 * l )  div  2447.0 into j
  put l - ( 2447.0 * j )  div  80 into d -- day
  put j  div  11 into l
  put j + 2 - ( 12 * l ) into m -- month
  put 100 * ( n - 49 ) + i + l into y -- year
end date.julian2DMY

/** get date.julian2DayOfWeek(aJulian)
@purpose Returns the day of the week according to: 1..7 for Sunday..Saturday
@param aJulian is the julian number.
*/
function date.julian2DayOfWeek aJulian
  --    // returns 1..7 for Sunday..Saturday
  return (aJulian+1) mod 7 + 1
end date.julian2DayOfWeek

--
Hope this help!


Joël Guillod