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      SUBROUTINE slCAYD (IY, IM, ID, NY, ND, J)

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      C A Y D
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  Gregorian calendar date to year and day in year (in a Julian
  calendar aligned to the 20th/21st century Gregorian calendar).

  (Includes century default feature:  use slCLYD for years
   before 100AD.)

  Given:
     IY,IM,ID   int    year, month, day in Gregorian calendar
                       (year may optionally omit the century)
  Returned:
     NY         int    year (re-aligned Julian calendar)
     ND         int    day in year (1 = January 1st)
     J          int    status:
                         0 = OK
                         1 = bad year (before -4711)
                         2 = bad month
                         3 = bad day (but conversion performed)

  Notes:

  1  This routine exists to support the low-precision routines
     slERTH, slMOON and slECOR.

  2  Between 1900 March 1 and 2100 February 28 it returns answers
     which are consistent with the ordinary Gregorian calendar.
     Outside this range there will be a discrepancy which increases
     by one day for every non-leap century year.

  3  Years in the range 50-99 are interpreted as 1950-1999, and
     years in the range 00-49 are interpreted as 2000-2049.

  Called:  slCLYD

  P.T.Wallace   Starlink   23 November 1994

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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