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% This file is public domain.
%
% These are the double-column macros from Paul Abrahams, Dec 1991
% They add the following features:
% \ifbalance (by default true, causes last page to be balanced)
% \everycolumn (a token list, useful for marks)
% \pageeject
% \eject does a column eject
\newtoks\mainoutput
\newbox\partialpage
\newdimen\fullvsize \newdimen \fullhsize
\newbox\leftcolumn \newbox \rightcolumn
\newbox\savefootins \newskip\footskip
\newbox\savetopins \newskip\topinsskip
\newif\ifbalance \balancetrue
\newtoks\everycolumn
\def\pageeject{\penalty -10005 }%
\def\doublecolumns{%
\mainoutput = \output % Save the previous \output.
%
% This grabs any single-column material.
\output = {\global\setbox\partialpage = \vbox{\unvbox255}}%
\vskip\abovedoublecolumnskip
\par % \par updates \pagetotal
\pagegoal = \pagetotal
\break % Now expand the \output we assigned just above.
\output = {\doublecolumnoutput}%
%
% Set up \hsize and \vsize for double columns.
\fullvsize = \vsize
\fullhsize = \hsize
\advance\hsize by -\gutter
\divide \hsize by 2
\advance\vsize by -\ht\partialpage
%
% Take account of existing insertions.
\ifvoid\footins\else
\advance\vsize by -\ht\footins
\advance\vsize by -\skip\footins
\fi
\setbox\savefootins = \box\footins
\footskip = \skip\footins
%
\ifvoid\topins\else
\advance\vsize by -\ht\topins
\advance\vsize by -\skip\topins
\fi
\setbox\savetopins = \box\topins
\topinsskip = \skip\topins
%
% Start at the left, clear the existing columns.
\let\lr = L%
\setbox0 = \box\leftcolumn \setbox0 = \box\rightcolumn
}%
%
% This routine actually does the outputting.
\def\doublecolumnoutput{%
\ifbalance\else \ifnum \outputpenalty < -10000
\setbox255 = \vbox{\unvbox255 \vfil}%
\fi\fi
%
\the\everycolumn
\if \lr L%
\buildcolumn\leftcolumn
\global\let\lr = R%
\else
\buildcolumn\rightcolumn
\global\let\lr = L%
\fi
%
\ifnum \outputpenalty < -10000
\ifbalance
\ifdim \ht\leftcolumn > 8\baselineskip
\balancecolumns
\global \let \lr = L%
\fi\fi\fi
%
\if \lr L%
\setbox255 = \vbox{%
\unvbox\partialpage
\dimen0 = \ht\leftcolumn \dimen1 = \dp\leftcolumn
\joincolumns
\ifnum \outputpenalty = -10005 \vfil \fi
}%
% The restoration of the insertion boxes happens only once, since
% they are empty thereafter.
\setbox\footins = \box\savefootins
\setbox\topins = \box\savetopins
\vsize = \fullvsize % Because we've taken care of \partialoutput
\ifnum \outputpenalty = -10006
\unvbox255
\else
\the\mainoutput
\global\vsize = \fullvsize
\fi
\fi
}%
%
%
% \joincolumns joins \leftcolumn and \rightcolumn into a vbox that aligns
% the tops of the two columns and has the depth of the deeper column.
% It adds the resulting box to the main vertical list.
%
\def\joincolumns{%
\dimen0 = \dp\leftcolumn \dimen1 = \dp \rightcolumn
\setbox0 = \hbox to \fullhsize{%
\vtop to \ht\leftcolumn{\unvbox\leftcolumn}%
\hfil
\vtop to \ht\rightcolumn{\unvbox\rightcolumn}%
}%
\dimen2 = \boxmaxdepth % For restoring it later
\ifdim \dimen0 < \dimen1
\boxmaxdepth = \dimen1
\else
\boxmaxdepth = \dimen0
\fi
\setbox0 = \vbox{\box0}%
\boxmaxdepth = \dimen2
\box0 % Produce for the calling context
}%
\def\buildcolumn #1{%
\ifnum \outputpenalty < -9999
\global \setbox #1 = \vbox{\pagecontents}%
\else
\global \setbox #1 = \vbox to \vsize{\pagecontents}%
\fi
}%
%
%
% Go back to single-column typesetting. Unfortunately, we cannot start
% a group in \doublecolumns and end it here, because some documents
% might want double-column mode to continue to the end. So we have to
% restore the things we've changed manually.
%
\def\singlecolumn{%
\penalty -10006
\output = \mainoutput
\hsize = \fullhsize
\vsize = \fullvsize
%
% Add \belowdoublecolumnskip if there's enough room, otherwise a \vfil
% to fill out the page.
\dimen0 = \pagetotal \advance \dimen0 by \belowdoublecolumnskip
\ifdim \dimen0 < \pagegoal
\vskip\belowdoublecolumnskip
\else
\vfil
\fi
\allowbreak
}%
%
\def \balancecolumns{%
\setbox\leftcolumn = \vbox{\unvbox\leftcolumn \unskip}%
\setbox\rightcolumn = \vbox{\unvbox\rightcolumn \unskip}%
\setbox0 = \vbox{%
\dimen0 = \dp\leftcolumn
\unvbox \leftcolumn
\if \lr L
\kern -\dimen0
\vskip -\topskip
\vskip \baselineskip
\unvbox \rightcolumn
\fi
}%
\dimen0 = \ht0
\advance \dimen0 by \topskip \advance \dimen0 by -\baselineskip
\divide \dimen0 by 2 \splittopskip = \topskip
\count@ = \vbadness \vbadness = 10000
\loop
\setbox2 = \copy0
\setbox1 = \vsplit2 to \dimen0
\ifdim \ht2 > \dimen0
\advance \dimen0 by 1pt
\repeat
\vbadness = \count@
\setbox \leftcolumn = \vbox to \dimen0{\unvbox1}%
\setbox \rightcolumn = \vbox to \dimen0{\unvbox2}%
}%
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