#  Calculate the calendar date (month, day, year) corresponding to
#  a Julian day number.  (Negative years are B.C.)
#  Based on algorithms published in Computer Language magazine,
#  December, 1990.  Used with permission.

proc caldate(jdate)
   local a, b, c, d, e, z, alpha, month, day, year
   set month = January February March April May June ^
      July August September October November December
   @ z = jdate + 1
   # Cope with the Gregorian calendar reform.
   if (z < 2299161) then
      @ a = z
      # Intercept years B.C.
      if (z < 1721423) @ a -= 366
   else
      @ alpha = (z - 1867216.25)//36524.25
      @ a = z + 1 + alpha - alpha//4
   end
   @ b = a + 1524
   @ c = (b - 122.1)//365.25
   @ d = floor(365.25 * c)
   @ e = (b - d)//30.6001
   @ day = b - d - floor(30.6001 * e)
   @ e -= e < 14 ? 2 : 14
   @ month = month[e]
   if ((year = e > 1 ? c - 4716 : c - 4715) == 0) @ year--
   return "$month $day $year"
end

caldate $argv