%------------------------------------------------------------------------------
% d a t e s . s t y   --  style file for inserting dates into documents
%------------------------------------------------------------------------------
% DESCRIPTION
% \today            generates today's date.  Alter this to suit the way you
%                   want it to appear.  It is currently set up to generate
%                   dates in the form `Saturday 14th October 1066'
%
% \thisdayofweek    generates today's day name (`Sunday', etc)
% \thisday          generates today's day (`1', `2', etc)
% \thisdayth        generates today's day (`1st', `2nd', etc),
%                   where the `st' etc are generated by \st etc
% \thismonth        generates today's month (`January', etc)
% \thisyear         generates today's year
%
% \dayofweek{year}{month}{day}  generates the day of the week for
%                   the given date
%
% \Sunday (etc)     generates `Sunday' (etc)
% \January (etc)    generates 'January' (etc)
%
% \stsup            generates a raised, reduced, underlined `st', as in 1st
% \ndsup            generates a raised, reduced, underlined `nd', as in 2nd
% \rdsup            generates a raised, reduced, underlined `rd', as in 3rd
% \thsup            generates a raised, reduced, underlined `th', as in 4th
% \raiseul          used by the above macros to raise and underline
%------------------------------------------------------------------------------
% REVISION HISTORY
% v1.00 1990-08-03 Adrian F. Clark <alien@essex.ac.uk>
%       Original version.
% v1.01 1992-08-04 Adrian F. Clark <alien@essex.ac.uk>
%        Corrected \dayofweek: it was generating additional spaces before the
%          day-name: this was significant in {tabular} environments, and
%          screwed up alignment no end.
%        Disabled the \phaseofmoon definitions, which are of little interest
%          to most people.
% v1.02 1994-05-13 Adrian F. Clark <alien@essex.ac.uk>
%       Changed \@x and \@y to \dates@x and \dates@y to circumvent name clash
%       with bezier.sty.
% v2.00 2002-03-07 Adrian F. Clark <alien@essex.ac.uk>
%       \th -> \thsup (etc) to avoid name clash with \th (thorn) in PS fonts;
%         THIS IS AN INCOMPATIBILITY, alas.
%       Removed a few vestigates of the phase of the moon computation.
%       Revised comments.
% v2.01 2003-08-14 Adrian F. Clark <alien@essex.ac.uk>
%       Added \now to generate the time as "hh:mm".
% v2.02 2003-11-15 Adrian F. Clark <alien@essex.ac.uk>
%       \alien@up -> \raiseul
%------------------------------------------------------------------------------
% TO-DO
% I suppose it'd be nice to take an optional argument, the language in which
% the text is to appear.  For example,
%   \usepackage[french]{dates}
% would make the dates appear in the form `Samedi 14 Octobre 1066'.  Or maybe
% this could be picked up from the babel option?
%------------------------------------------------------------------------------
% Copyright 1990-2002 Adrian F. Clark <alien@essex.ac.uk>  All rights reserved.
%------------------------------------------------------------------------------


%------------------------------------------------------------------------------
% The actual date macros.
%------------------------------------------------------------------------------

% \today generates today's date in the style `Saturday 14th October 1066'

\def\today{\thisdayofweek\ \thisdayth\ \thismonth\ \thisyear}

\def\thisday{\number\day}

\def\thisdayth{\thisday \ifcase\day
  \or\stsup\or\ndsup\or\rdsup\or\thsup\or\thsup
  \or\thsup\or\thsup\or\thsup\or\thsup\or\thsup
  \or\thsup\or\thsup\or\thsup\or\thsup\or\thsup
  \or\thsup\or\thsup\or\thsup\or\thsup\or\thsup
  \or\stsup\or\ndsup\or\rdsup\or\thsup\or\thsup
  \or\thsup\or\thsup\or\thsup\or\thsup\or\thsup
  \or\stsup\fi}

\def\thisdayofweek{\dayofweek{\year}{\month}{\day}}

\def\thismonth{\ifcase\month\or \January\or \February\or \March\or
  \April\or \May\or \June\or \July\or \August\or \September\or
  \October\or \November\or \December\fi}

\def\thisyear{\number\year}

%------------------------------------------------------------------------------
% Names of days of the week and the months.  This makes it easier to change
% them for languages other than English (that's why they're not \@Sunday, etc).
%------------------------------------------------------------------------------

\def\Sunday{Sunday}
\def\Monday{Monday}
\def\Tuesday{Tuesday}
\def\Wednesday{Wednesday}
\def\Thursday{Thursday}
\def\Friday{Friday}
\def\Saturday{Saturday}

\def\January{January}
\def\February{February}
\def\March{March}
\def\April{April}
\def\May{May}
\def\June{June}
\def\July{July}
\def\August{August}
\def\September{September}
\def\October{October}
\def\November{November}
\def\December{December}

%------------------------------------------------------------------------------
% Counters.  Note that we use the same registers as TeX holds other things in
% (e.g., \count0 holds the page number).  This requires that \@savestyle,
% \@setstyle and \dayofweek do all their register manipulations within a
% group.  This is a bit messy but it saves having eight registers permanently
% set aside just for date calculation.
%------------------------------------------------------------------------------

\def\@cent{\count0 }                       % century number (1979 == 20)
\def\@diy{\count1 }                        % day in the year
\def\@dow{\count2 }                        % gets day of the week
\def\@epact{\count3 }                      % age of the moon on Jan. 1
\def\@golden{\count4 }                     % Moon's golden number
\def\@leap{\count5 }                       % leap year
\def\dates@x{\count6 }                     % temp register
\def\dates@y{\count7 }                     % another temp register

%------------------------------------------------------------------------------
% For `old' (pre-version-2.10) LaTeX, these macros ensure the smaller text
% comes out in the right font by saving the font family before reducing the
% size, then restoring it.  (This hack was suggested by Leslie Lamport.)  Of
% course, it requires that the font in use when the caller is invoked has
% a sensible family.  For LaTeX 2.10 onwards, including LaTeX2e, which uses
% the font selection scheme due to Mittelbach and Sh\"oepf, such a hack is not
% necessary.  The macros detect which version is in use automagically.
%------------------------------------------------------------------------------

\def\stsup{\raiseul{st}}
\def\ndsup{\raiseul{nd}}
\def\rdsup{\raiseul{rd}}
\def\thsup{\raiseul{th}}

\def\raiseul#1{{\@savestyle\thinspace$^{\underline{\hbox{%
  \scriptsize\@setstyle#1\fam=-1 }}}$}}

% Macros to save and restore the font family.

\def\@savestyle{\count0=\the\fam}

\def\@setstyle{\ifcase\count0\rm\or\mit\or\cal\or\rm% what's family 3?
  \or\it\or\sl\or\bf\or\tt\fi}

%------------------------------------------------------------------------------
% The time.
%------------------------------------------------------------------------------

\def\@hour{\count0 }
\def\@min{\count1 }

\def\now{{\@hour=\time \@min=\@hour \divide\@hour by 60\relax
  \ifnum\@hour <10
    0\number\@hour \else \number\@hour \fi
  :\relax
  \multiply\@hour by 60 \advance\@min by -\@hour
  \ifnum\@min <10
    0\number\@min \else \number\@min \fi}}


%------------------------------------------------------------------------------
% The nitty-gritty.
%------------------------------------------------------------------------------

% The day of the week (\Sunday, etc.) is inserted into the text by
% \dayofweek. (This uses registers \@dow, \@leap, \dates@x and \dates@y.)  I
% acquired this from elsewhere; it was apparently written by Martin Minow, now
% a DEC employee.  The algorithm is:
%   leap = year + (month - 14)/12;
%   dow = (13 * (month + 10 - (month + 10)/13*12) - 1)/5
%   dow += day + 77 + 5 * (leap % 100)/4
%   dow += leap / 400
%   dow -= leap / 100 * 2
%   dow = (dow % 7)

\def\dayofweek#1#2#3{{\@leap=#2\advance\@leap by -14\divide\@leap by 12\relax
  \advance\@leap by #1\relax
  \@dow=#2\advance\@dow by 10\relax
  \dates@y=\@dow \divide\dates@y by 13\multiply\dates@y by 12\relax
  \advance\@dow by -\dates@y \multiply\@dow by 13\relax
     \advance\@dow by -1 \divide\@dow by 5\relax
  \advance\@dow by #3\advance\@dow by 77\relax
  \dates@x=\@leap \dates@y=\dates@x \divide\dates@y by
  100\multiply\dates@y by 100\relax \advance\dates@x by -\dates@y \relax
  \multiply\dates@x by 5\divide\dates@x by 4\advance\@dow by \dates@x
  \dates@x=\@leap \divide\dates@x by 400\advance\@dow by \dates@x
  \dates@x=\@leap \divide\dates@x by 100\multiply\dates@x by 2\relax
  \advance\@dow by -\dates@x \dates@x=\@dow \divide\dates@x by 7\relax
  \multiply\dates@x by 7\advance\@dow by -\dates@x
  \ifcase\@dow \Sunday\or \Monday\or \Tuesday\or \Wednesday\or
      \Thursday\or \Friday\or \Saturday\fi}}

\endinput


% Likewise, \phaseofmoon inserts the phase of the moon into the text. This was
% written by the same person as \dayofweek.  The routine calculates the year's
% epact (the age of the moon on Jan 1.), adds this to the number of days in
% the year, and calculates the phase of the moon for this date.  It returns
% the phase as a string, e.g., \NewMoon, \FullMoon, etc.
% In the algorithm:
%   diy       is the day of the year - 1 (i.e., Jan 1 is day 0).
%   golden    is the number of the year in the Mentonic cycle, used to
%             determine the position of the calender moon. 
%   epact     is the age of the calender moon (in days) at the beginning
%             of the year.  To calculate epact, two century-based
%             corrections are applied:
%             Gregorian:      (3 * cent)/4 - 12
%                is the number of years such as 1700, 1800 when leap year was
%                not held.
%             Clavian:      (((8 * cent) + 5) / 25) - 5
%                is a correction to the Mentonic cycle of about 8 days every
%                2500 years.  Note that this will overflow 16 bits in the year
%                409600: beware. ;-)
% The algorithm is accurate for the Gregorian calender only.
% The magic numbers used in the phase calculation are:
%   29.5      The moon's period in days.
%  177        29.5 scaled by 6
%   22        (29.5 / 8) scaled by 6 (this gets the phase)
%   11        ((29.5 / 8) / 2) scaled by 6
% Theoretically, this should yield a number in the range 0--7.  However,
% two days per year, things don't work out too well.

% Epact is calculated by the algorithm given in Knuth vol. 1 (Calculation
% of Easter).  See also the article on Calenders in the Encyclopaedia
% Britannica and Knuth's algorithm in CACM April 1962, page 209.

\def\NewMoon{new}
\def\WaxCresMoon{waxing crescent}
\def\FirstQuarterMoon{in its first quarter}
\def\WaxGibMoon{waxing gibbous}
\def\FullMoon{full}
\def\WaneGibMoon{waning gibbous}
\def\LastQuarterMoon{in its last quarter}
\def\WaneCresMoon{waning crescent}

\def\phaseofmoon#1#2#3{{%
  \@diy=#3 \advance\@diy by \ifcase#2                  % Jan 1 == 0
      -1\or -1\or 30\or 58\or 89\or 119\or 150\or      % Jan .. Jun
      180\or 211\or 241\or 272\or 303\or 333\fi        % Jul .. Dec
%            if ((month > 2) && ((year % 4 == 0) &&
%                ((year % 400 == 0) || (year % 100 != 0))))
%                  diy++;            /* Leapyear fixup      */
  \ifnum #2>2
    \dates@x=#1 \dates@y=\dates@x \divide\dates@y by 4 \multiply
      \dates@y by 4 \advance\dates@x by -\dates@y
    \ifnum \dates@x=0               % month > 2 and maybe leap year
      \dates@x=#1 \dates@y=\dates@x \divide\dates@y by 400 \multiply
        \dates@y by 400 \advance\dates@x by -\dates@y
      \ifnum \dates@x=0             % 2000 is a leap year
      \advance\@diy by 1            % so it's one day later
      \else                         % not 2000, check other '00's
      \dates@x=#1 \dates@y=\dates@x \divide\dates@y by 100 \multiply
        \dates@y by 100 \advance\dates@x by -\dates@y
      \ifnum \dates@x>0             % not some other '00' year
          \advance\@diy by 1        % it's still one day later
      \fi                           % not odd century
      \fi                           % not 2000-type century
    \fi                             % not leapish year
  \fi                               % not march or later
% cent = (year / 100) + 1;      // Century number
% golden = (year % 19) + 1;     // Golden number
  \@cent=#1 \divide\@cent by 100 \advance\@cent by 1
  \@golden=#1
  \dates@y=#1 \divide\dates@y by 19 \multiply\dates@y by 19
    \advance\@golden by -\dates@y
  \advance\@golden by 1
% epact = ((11 * golden) + 20             // Golden number
%       + (((8 * cent) + 5) / 25) - 5     // 400 year cycle
%       - (((3 * cent) / 4) - 12)) % 30;  // Leap year correction
  \@epact=11 \multiply\@epact by \@golden
  \advance\@epact by 20
  \dates@x=8 \multiply\dates@x by \@cent \advance\dates@x by 5
  \divide\dates@x by 25 \advance\dates@x by -5
  \advance\@epact by \dates@x
  \dates@x=3 \multiply\dates@x by \@cent \divide\dates@x by 4
    \advance\dates@x by -12
  \advance\@epact by -\dates@x
  \dates@y=\@epact \divide\dates@y by 30 \multiply\dates@y by 30
    \advance\@epact by -\dates@y
% if (epact <= 0)
%   epact += 30;                  // Age range is 1--30
% if ((epact == 25 && golden > 11) || epact == 24)
%    epact++;
  \ifnum \@epact<0
    \advance\@epact by 30
  \fi
  \ifnum \@epact=25
    \ifnum \@golden>11
      \advance \@epact by 1
    \fi
  \else
    \ifnum \@epact=24
      \advance \@epact by 1
    \fi
  \fi
% Calculate the phase, using the magic numbers defined above.
% Note that phase may be equal to 8 (== 0) on two days of the year
% due to the way the algorithm was implemented.
%   phase = (((((diy + epact) * 6) + 11) % 177) / 22) & 7;
  \dates@x=\@diy \advance\dates@x by \@epact \multiply\dates@x by 6
    \advance\dates@x by 11
  \dates@y=\dates@x \divide\dates@y by 177 \multiply\dates@y by 177
    \advance\dates@x by -\dates@y
  \divide\dates@x by 22
  \ifcase\dates@x \NewMoon\or \WaxCresMoon\or \FirstQuarterMoon\or
      \WaxGibMoon\or \FullMoon\or \WaneGibMoon\or
      \LastQuarterMoon\or \WaneCresMoon\or \NewMoon\fi}}

%------------------------------------------------------------------------------
% End of dates.sty
%------------------------------------------------------------------------------