source: trunk/SRC/Calendar/leapyr.pro

;+
;
; @file_comments
; determine whether the input year is a leap year or not
; Very useful for finding number of days in a year.
; eg. NUM_DAYS_IN_YR = 365 + leapyr(year)
;
; @categories
; Calendar
;
; @param year {in}{required} {type= scalar or array}
; year to be tested as a leap year.
;
; @returns
; 0 then not a leap year, 1 then year is a leap year
; with the same number of elements than year.
;
; @uses
; <pro>cm_4cal</pro>
;
; @examples
;   IDL> result = leapyr(2000)
;
; @history
;
; Originally Written by: Trevor Harris, Physics Dept., University of Adelaide,
;20/09/88
;
; November 2004: correction for century years... S. Masson;
;
; Every year divisible by 4 is a leap year.
; But every year divisible by 100 is NOT a leap year
; Unless the year is also divisible by 400, then it is still a
; leap year.
; This means that year 1800, 1900, 2100, 2200, 2300 and 2500 are
; NOT leap years, while year 2000 and 2400 are leap years.
; + suppress the automatic change 89 -> 1989
;
; June 2005 update for new commons, Sebastien Masson.
;
; @version
; $Id$
;
;-
FUNCTION leapyr, year
;
  compile_opt idl2, strictarrsubs
;
@cm_4cal
  yr = long(year)
  IF n_elements(key_caltype) EQ 0 THEN key_caltype = 'greg'
;
  IF key_caltype NE 'greg' THEN BEGIN
    sd = size(yr, /dimensions)
    IF sd[0] EQ 0 THEN return, 0b ELSE return, bytarr(size(yr, /dimensions))
  ENDIF ELSE return, (yr MOD 4 EQ 0)*((yr MOD 100 NE 0) + (yr MOD 400 EQ 0))

end