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      SUBROUTINE slCLYD (IY, IM, ID, NY, ND, JSTAT)

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

  Given:
     IY,IM,ID   i    year, month, day in Gregorian calendar

  Returned:
     NY         i    year (re-aligned Julian calendar)
     ND         i    day in year (1 = January 1st)
     JSTAT      i    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  The essence of the algorithm is first to express the Gregorian
     date as a Julian Day Number and then to convert this back to
     a Julian calendar date, with day-in-year instead of month and
     day.  See 12.92-1 and 12.95-1 in the reference.

  Reference:  Explanatory Supplement to the Astronomical Almanac,
              ed P.K.Seidelmann, University Science Books (1992),
              p604-606.

  P.T.Wallace   Starlink   26 November 1994

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

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