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View File perl-Date-Day.spec of Package perl-Date-Day (Project devel:languages:perl:CPAN-D)

# spec file for package perl-Date-Day
# Copyright (c) 2012 SUSE LINUX Products GmbH, Nuernberg, Germany.
# All modifications and additions to the file contributed by third parties
# remain the property of their copyright owners, unless otherwise agreed
# upon. The license for this file, and modifications and additions to the
# file, is the same license as for the pristine package itself (unless the
# license for the pristine package is not an Open Source License, in which
# case the license is the MIT License). An "Open Source License" is a
# license that conforms to the Open Source Definition (Version 1.9)
# published by the Open Source Initiative.

# Please submit bugfixes or comments via http://bugs.opensuse.org/

Name:           perl-Date-Day
Version:        1.04
Release:        0
%define cpan_name Date-Day
Summary:        Perl extension for converting a date to its respective day.
License:        CHECK(GPL-1.0+ or Artistic-1.0)
Group:          Development/Libraries/Perl
Url:            http://search.cpan.org/dist/Date-Day/
Source:         http://www.cpan.org/authors/id/E/ES/ESSENZ/%{cpan_name}-%{version}.tar.gz
BuildArch:      noarch
BuildRoot:      %{_tmppath}/%{name}-%{version}-build
BuildRequires:  perl
BuildRequires:  perl-macros
#BuildRequires: perl(Date::Day)

After noticing the complexity of some modules for determining the day of a
specific date, I decided to write this module. It is by far the shortest
module of its kind performing the above task. This module exports a
subroutine called day() which takes as arguments numerical month, day, and
year. See Synopsis for example. As far as range of usage, the day()
function will return a proper day for all dates starting from year 0
through infinity. There are no restrictions. If you pass bad data to the
function, a day will still be returned, it just won't have any meaning. So
March 45, 2001 will return a day, just one with no meaning. So make sure
you pass real dates.

After initial release of this module, I decided to elaborate on the
mathematical foundations for the algorithm used. Most other day of week
modules use the dooms day algorithm. Date::Day uses a single line formula.

Not getting into too much detail, we take the fact that March 1, 0000 fell
on a Wednesday. Knowing this, we can determine the day of week March 1 will
fall on in any given year y > 0. That is:

	3 + y + [y/4] - [y/100] + [y/400] mod 7

[y/4] represents the integer part of (year) divided by (4). Weekdays
correspond to the following numbers:

Sun Mon Tue Wed Thu Fri Sat 0 1 2 3 4 5 6

So for example, look at March 1, 1994:

	3 + 1994 + [1994/4] - [1994/100] + [1994/400] mod 7 = 2 mod 7

And so March 1, 1994 is a Tuesday. So now we can find the day of week for
March 1 in any given year. How do we find the day corresponding to a date
other than March 1? Since March 1, 0000 has number 3 (Wednesday), than
April 1, 0000 has number 3 + 31 mod 7 = 6 mod 7 since March has 31 days. We
can do the same thing for May, June and so on. Thus giving the following

(Day of week for first day in given month in year 0000)

Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec 1 Jan 1 Feb 1 3 6
1 4 6 2 5 0 3 5 1 4

And we treat March as month 1, April as month 2, and so on. We denote these
numbers by 1 + j(m), where j(m), for m=1,2,...,12 (with m=1 as March, m=2
as April, and so on), is defined by:


So we refine our table:

Month 1 2 3 4 5 6 7 8 9 10 11 12 Value 0 3 2 5 0 3 5 1 4 6 2 4

The above table is very important in our final formula. So for example, the
month June is numerical 6, and 6 goes to value 3. 3 is then used in our
final formula.

With all the above data, it follows that month m, day 1, year y, has day of
week number:

	1 + j(m) + y + [y/4] - [y/100] + [y/400] mod 7

And to get a formula that handles any given day, we use the formula:

	d + j(m) + y + [y/4] - [y/100] + [y/400] mod 7       (***)

So for example, we want to find the day of week corresponding to April 8,
2002. If March is month 1, then April is month 2, hence m=2. So j(2)=5.
Thus we have:

	8 + 5 + 2002 + [2002/4] - [2002/100] + [2002/400] mod 7

	which is, 1 mod 7. So 4/8/2002 is a Monday.

So when you look at the code portion of Day.pm you see only two important
lines of code. One line is for the associative array that implements j(m).
The other line is for implementing formula (***). Thats it.

%setup -q -n %{cpan_name}-%{version}

%{__perl} Makefile.PL INSTALLDIRS=vendor
%{__make} %{?_smp_mflags}

%{__make} test


%files -f %{name}.files
%doc Changes README