%\DayOfWeekexpands to the day of the week ("Sunday", etc.)
%\PhaseOfMoonexpands to the phase of the moon
%
%Written by Martin Minow of DEC (minow%bolt.dec@decwrl.dec.com).
%
  \newcount\dow % Gets day of the week
  \newcount\leap % Leap year fingaler
  \newcount\x % Temp register
  \newcount\y % Another temp register
\def\DayOfWeek\%
%
% Calculate day of the week, return "Sunday", etc.
%
% \newcount\dow % Gets day of the week
% \newcount\leap % Leap year fingaler
% \newcount\x % Temp register
% \newcount\y % Another temp register
%leap = year + (month - 14)/12;
  \leap=\month \advance\leap by -14 \divide\leap by 12
  \advance\leap by \year
%dow = (13 * (month + 10 - (month + 10)/13*12) - 1)/5
  \dow=\month \advance\dow by 10
  \y=\dow \divide\y by 13 \multiply\y by 12
  \advance\dow by -\y \multiply\dow by 13 \advance\dow by -1 \divide\dow by 5
%dow += day + 77 + 5 * (leap % 100)/4
  \advance\dow by \day \advance\dow by 77
  \x=\leap \y=\x \divide\y by 100 \multiply\y by 100 \advance\x by -\y
  \multiply\x by 5 \divide\x by 4 \advance\dow by \x
%dow += leap / 400
  \x=\leap \divide\x by 400 \advance\dow by \x
%dow -= leap / 100 * 2;
%dow = (dow % 7)
  \x=\leap \divide\x by 100 \multiply\x by 2 \advance\dow by -\x
  \x=\dow \divide\x by 7 \multiply\x by 7 \advance\dow by -\x
  \ifcase\dow Sunday\or Monday\or Tuesday\or Wednesday\or
Thursday\or Friday\or Saturday\fi
\
%%
%%
%%
  \newcount\cent% Century number (1979 == 20)
  \newcount\epact% Age of the moon on Jan. 1
  \newcount\diy% Day in the year
  \newcount\golden% Moon's golden number
  \newcount\x% Temp
  \newcount\m% Temp for modulus
\def\PhaseOfMoon\%Calculate the phase of the (civil) moon.
%
% 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.,
% "new", "full", etc.
%
% In the algorithm:
%
%diyIs the day of the year - 1 (i.e., Jan 1 is day 0).
%
%goldenIs the number of the year in the Mentonic cycle, used to
%determine the position of the calender moon.
%
%epactIs 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 as follows:
% 29.5The moon's period in days.
%17729.5 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.
%
  \diy=\day \advance\diy by \ifcase\month% 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 \month>2
    \x=\year \m=\x \divide\m by 4 \multiply\m by 4 \advance\x by -\m
    \ifnum \x=0% month > 2 and maybe leapyear
      \x=\year \m=\x \divide\m by 400 \multiply\m by 400 \advance\x by -\m
      \ifnum \x=0% 2000 is a leap year
\advance\diy by 1% so it's one day later
      \else% not 2000, check other '00's
\x=\year \m=\x \divide\m by 100 \multiply\m by 100 \advance\x by -\m
\ifnum \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=\year \divide\cent by 100 \advance\cent by 1
  \golden=\year
  \m=\year \divide\m by 19 \multiply\m by 19 \advance\golden by -\m
  \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
  \x=8 \multiply\x by \cent \advance\x by 5
  \divide\x by 25 \advance\x by -5
  \advance\epact by \x
  \x=3 \multiply\x by \cent \divide\x by 4 \advance\x by -12
  \advance\epact by -\x
  \m=\epact \divide\m by 30 \multiply\m by 30 \advance\epact by -\m
%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;
%
  \x=\diy \advance\x by \epact \multiply\x by 6 \advance\x by 11
  \m=\x \divide\m by 177 \multiply\m by 177 \advance\x by -\m
  \divide\x by 22
  \ifcase\x new\or waxing crescent\or in its first quarter\or
waxing gibbous\or full\or waning gibbous\or
in its last quarter\or waning crescent\or new\fi
