% From: minow@decvax.UUCP (Martin Minow)
%
% \DayOfWeek expands to the day of the week ("Sunday", etc.)
%
\newcount\dow
\def\DayOfWeek{\ifcase\dow Sunday\or Monday\or Tuesday\or Wednesday\or
Thursday\or Friday\or Saturday\fi}
%
% Calculate day of the week (0=Sunday, 1=Monday, etc.), result
% into \dow.
%
{ \countdef\leap=1 % Leap year fingaler
\countdef\x=2 % Temp register
\countdef\y=3 % 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
\global\dow=\dow
}