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calendar_module.f90
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calendar_module.f90
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module calendar_module
! provides date utility fuctions
use kind_module, only : i4b
use string_module, only : string_tolower
implicit none
character(len=*), dimension(12), parameter, public :: calendar_monthnames = &
(/"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"/)
character(len=*), dimension(0:6), parameter, public :: calendar_weekdaynames = &
(/"Sun","Mon","Tue","Wed","Thr","Fri","Sat"/)
public :: calendar_isleapyear, calendar_daysinmonth, &
calendar_weekday, calendar_dayofyear, calendar_date, &
calendar_pentad, calendar_pentaddates, calendar_ndays
contains
function calendar_isleapyear(y) result(d)
! returns d=1 if argument y is a leap year otherwise d=0
implicit none
integer(kind=i4b), intent(in) :: y
integer(kind=i4b) :: d
d = 0
if (modulo(y,4)==0) then
if (modulo(y,100)/=0) then
d = 1
else
if (modulo(y,400)==0) then
d = 1
end if
end if
end if
end function calendar_isleapyear
function calendar_daysinmonth(y,m) result(d)
! returns the number of days in the month
implicit none
integer(kind=i4b), intent(in) :: y, m
integer(kind=i4b) :: d
select case(m)
case(4,6,9,11)
d = 30
case(2)
d = 28 + calendar_isleapyear(y)
case default
d = 31
end select
end function calendar_daysinmonth
function calendar_weekday(y,m,d) result(w)
! returns the day of the week using Zeller's algorithm
! 0-6 correspond to Sun-Sat
implicit none
integer(kind=i4b), intent(in) :: y, m, d
integer(kind=i4b) :: x,n,w
x = y
n = m
! treat Jan and Feb as 13th and 14th months of the previous year
if (m<=2) then
n = n + 12
x = x - 1
end if
w = modulo((d-1+(13*(n+1)/5)+x+x/4-x/100+x/400),7)
end function calendar_weekday
function calendar_dayofyear(y,m,d) result(n)
! returns the day of the year
implicit none
integer(kind=i4b), intent(in) :: y, m, d
integer(kind=i4b) :: i, n
n = d
do i=1, m-1
n = n + calendar_daysinmonth(y,i)
end do
end function calendar_dayofyear
function calendar_date(y,n) result(ymd)
! returns year, month, date from the year and day of the year
implicit none
integer(kind=i4b), intent(in) :: y, n
integer(kind=i4b) :: x, m, d, k
integer(kind=i4b), dimension(3) :: ymd
x = y
m = 1
d = n
substloop: do
k = calendar_daysinmonth(x,m)
if (d <= k) then
exit substloop
else
if (m<12) then
m = m + 1
else
x = x + 1
m = 1
end if
d = d - k
end if
end do substloop
ymd(1) = x
ymd(2) = m
ymd(3) = d
end function calendar_date
function calendar_pentad(y,m,d) result(p)
! returns pentad the date(y,m,d) belogs to
implicit none
integer(kind=i4b), intent(in) :: y, m, d
integer(kind=i4b) :: l,x,p
integer(kind=i4b), parameter :: z = 60 ! 29 Feb
l = calendar_isleapyear(y)
x = calendar_dayofyear(y,m,d)
if (x>z) then
x = x - l
end if
p = (x-1)/5 + 1
end function calendar_pentad
function calendar_pentaddates(p) result(n)
! returns the beginning and ending dates of the pentad
implicit none
integer(kind=i4b), intent(in) :: p
integer(kind=i4b), dimension(4) :: n
integer(kind=i4b), dimension(3) :: b, e
integer(kind=i4b) :: d
integer(kind=i4b), parameter :: y = 1999 ! non-leap dummy year
d = (p-1)*5+1
b = calendar_date(y,d)
e = calendar_date(y,d+4)
n(1:2) = b(2:3)
n(3:4) = e(2:3)
end function calendar_pentaddates
function calendar_ndays(y1,m1,d1,y2,m2,d2) result(n)
! returns number of days
implicit none
integer(kind=i4b), intent(in) :: y1, m1, d1, y2, m2, d2
integer(kind=i4b) :: n
integer(kind=i4b) :: n1, n2, m, ny, y
n1 = calendar_dayofyear(y1,m1,d1)
n2 = calendar_dayofyear(y2,m2,d2)
ny = y2-y1
m = 0
do y=y1, y2-1
m = m + calendar_isleapyear(y)
end do
n = max(0,n2 + ny*365 + m - n1 + 1)
end function calendar_ndays
end module calendar_module