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% abidir.sty
% ArabTeX macros for bidirectional linebreaking
% 21.12.95
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% (c) Klaus Lagally
%     Institut fuer Informatik
%     Universitaet Stuttgart
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\ifx \bidiratcode \undefined \else \xpa \endinput \fi

\chardef \bidiratcode = \catcode`\@            \catcode`\@ = 11

\a@ident {abidir.sty} {3.04 bidirectional linebreaking } {21.12.95}

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% <LR insertion inside Rtext>
%\def \test@insert #1>{\a@Linsert {#1}}

% \LR{#1} = LR insertion inside Rtext
\def \a@c@LR {\unarab@codes \a@Linsert }
\let \a@c@L \a@c@LR	% usage: \L {LR text}

% \LR{#1} = LR insertion inside Ltext: trivial
\let \LR \relax 	\let \L \relax 

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% \RL{#1} = RL insertion inside Ltext
\def \RL {\protect \a@RL }
\let \R \RL		% usage: \R {RL text}

% \RL{#1} = RL insertion inside Rtext: trivial
\def \a@c@RL #1{\test@token #1 } 	\let \a@c@R \a@c@RL

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\def \goodpar {% 	usage: \goodpar {Roman paragraphs}
% put around one or more paragraphs if the linebreaking is bad
% caution: may lead to storage overflow
\dimen0 \prevdepth \setbox0 \vbox \bgroup \prevdepth \dimen0
\def \par {\egroup \endgraf \goodpar x}% dummy character
\aftergroup \g@@dpar \let \next=}

\def \g@@dpar {\unvbox0 }

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\newdimen \a@Llength	\newdimen \a@Lwidth	\newdimen \a@Lindent	
\newdimen \a@Rlength	\newdimen \a@Rheight	\newdimen \a@splitht
\newbox \insertb@x	\newbox \a@spacebox
\newbox \a@Rboxi	\newbox \a@Rboxii
\newbox \a@Rdummyi	\newbox \a@Rdummyii	\newif \ifR@split
\newdimen \a@baselineskip

\def \ins@skip {\hskip \z@ plus 0.1em }% before and after insertion

\def \a@vglue {\z@ plus 2ex }% glue at top of the insertion \vbox

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\def \a@RL {% RL insertion inside Ltext
\bgroup \arab@codes \set@arabfont \@waslafalse \@wasfalse \a@@Rinsert }

\def \a@@Rinsert #1{% RL insertion inside Ltext
\ifshow \a@verb #1>\fi % 	verbating listing
\ifarab \a@Rinsert {#1} \fi % 	arabic writing 
\iftrans \set@transfont \trans@text #1 \end \/\fi
\ifnum \tracingarab > \@ne \message {>}\fi
\unskip \egroup }

\def \a@Rinsert #1{% put a sequence of RL words into Ltext
\leavevmode % go to hmode if not there already
\ifinner \arab@sequence #1>% inside a \hbox: append
\else \a@Rsplit {#1}% splice into the current paragraph
\fi }

\def \a@Rsplit #1{% splice RL words into the current paragraph
\bgroup \def \next@command {\test@special}\transfalse \showfalse 
  \def \arab@space {\space }% no infinite stretch !!
  \a@splitht 3.5ex \def \tat@skip {0.04ex plus 0.5ex }%
  \a@Rdimen {#1}% 	get the length of the first 2 RL words
\ifdim \wd\a@Rboxii = \z@ 
  \unhbox\a@Rboxi % 	done with the insertion
\else \a@Ldimen % 	get the dimensions of the last line
  \a@Rtobox {#1}% 	pack the insertion lines into a \vbox
  \a@Runpack % 		unpack and splice into the current paragraph
\fi \egroup }

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\def \a@Rdimen #1{% get the dimensions of the first two words
\a@Rfirst #1 \to \a@wordi \a@Rrest
\xpa \a@Rwordtobox \a@wordi \to \a@Rboxi \a@Rdummyi
\xpa \ifx \xpa \relax \a@Rrest \relax \def \a@wordii {}%
\else \xpa \a@Rfirst \a@Rrest \to \a@wordii \a@Rrest \fi 
\xpa \a@Rwordtobox \a@wordii \to \a@Rboxii \a@Rdummyii }

\def \a@Rwordtobox #1\to #2#3{% Rword to \box#2, Rdummy to \box#3
\setbox#2\hbox {\spreadtrue \arab@strut \arab@sequence #1>%
		\setbox0 \lastbox \unhbox0 }%
\setbox#3\hbox to \wd#2{\hfill }\ht#3\ht#2\dp#3\z@}

\def \a@Rfirst #1 #2\to #3#4{% split off first word
\ifx \relax #1\relax 
\ifx \relax #2\relax \def #3{#1}\def #4{#2}\else
\a@Rfirst #2 \to #3#4\fi
\else \def #3{#1}\def #4{#2}\fi }

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\def \a@Ldimen {% get the dimensions of the preceding line
\setbox\a@spacebox \hbox {\arab@space}\tolerance 10000
\R@splitfalse \leavevmode \copy \a@Rdummyi \arab@space \copy \a@Rdummyii
\parfillskip \z@ plus 1fill
$$\global \a@Llength \predisplaysize % 		dummy display
\global \a@Lwidth \displaywidth \global \a@Lindent \displayindent 
\hbox to \a@Lwidth {}\postdisplaypenalty \@M
$$ {\endgraf }% keep paragraph parameters
\prevdepth -\baselineskip
\a@Ladjust % update \a@Llength and \a@Lindent
\ifinner \a@killdisplay \else \a@skipback \fi }

\def \a@Ladjust {% correct \a@Llength and \a@Lindent
\ifdim \a@Llength = \maxdimen \a@Llength \a@Lwidth %	flexible line
\else \advance \a@Llength -2em \advance \a@Llength -\a@Lindent 
\fi 
\advance \a@Llength -\leftskip \advance \a@Llength -\wd\a@Rdummyii
\ifdim \a@Llength = \z@ \R@splittrue \a@Llength \a@Lwidth 
	\advance \a@Llength -\leftskip \advance \a@Llength -\rightskip
\else \advance \a@Llength -\wd\a@spacebox
\fi \advance \a@Llength -\wd\a@Rdummyi }

\def \a@killdisplay {% vbox: get back to the old position
\unskip \unskip \unpenalty \setbox0 \lastbox % get rid of garbage
\ifR@split \unskip \unskip \unpenalty \setbox0 \lastbox \fi
\unskip \unskip \unpenalty \setbox0 \lastbox % last line
\dimen0 \baselineskip \advance \dimen0 -\ht0
\advance \dimen0 -\lastskip \prevdepth \dimen0
\unskip \vskip -\parskip 
\noindent \unhbox0 % open and trim last line 
\unskip \unskip \unpenalty \setbox0 \lastbox 
\ifR@split \else \unskip \setbox0 \lastbox \fi }

\def \a@skipback {% paragraph: get back to the old position
\vskip -\belowdisplayskip \vskip -3\baselineskip 
\vskip -\abovedisplayskip \vskip -\parskip 
\ifR@split \ifdim \z@ > \lineskiplimit \vskip -\baselineskip \else
\vskip -\ht\a@Rdummyii \vskip -\dp\a@Rboxi \vskip -\lineskip
\fi\fi \noindent \arab@strut \nobreak \hskip \a@Llength }

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\def \a@Rtobox #1{% pack the insertion into \insertb@x
\setbox \insertb@x \vbox {\a@hsize \a@Lwidth 
\advance \a@hsize -\leftskip \advance \a@hsize -\rightskip
\a@limit \a@hsize \leftskip \z@ \rightskip \z@ 
\parfillskip \z@ plus 1fil \relax \parskip \z@
\def \arab@space {\nobreak \space }% no infinite stretch !!
\let \a@@kern \a@kern \let \a@@mkern \a@mkern
\def \a@kern {\nobreak \a@@kern}\def \a@mkern {\nobreak \a@@mkern}%
\let \end \relax \spreadtrue \vskip \a@vglue \hbadness 10000
\putlineb@x {\arab@strut \hskip \a@Llength }\a@spacefalse 
\test@token #1 \end \unskip \unskip \vskip \a@vglue 
\hbox {\box\lineb@x \hfill }}}

\def \a@Runpack {\ins@skip % unpack all lines from the insertion
\loop \a@Rgetline \unhbox \tempb@x \unskip \unskip \break
\ifvbox \insertb@x \repeat \unpenalty \ins@skip }

\def \a@Rgetline {% unpack the next line globally to \box \tempb@x
\splittopskip \a@vglue \setbox \tempb@x \vsplit \insertb@x to \a@splitht 
\setbox0 \vbox {\unvbox \tempb@x \setbox2 \lastbox \unhbox2 
\unskip \unskip \unpenalty \global \setbox \tempb@x \lastbox }}

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\def \a@Linsert #1{% splice Ltext into RL paragraph
\a@spacetrue \putwordb@x {\ins@skip }\dimen0 \wd \lineb@x 
\setbox \insertb@x \vbox
{\rm \parskip \z@ \hangindent -\dimen0 \hangafter -\@ne 
\rightskip \z@ plus .001fil \vskip \a@vglue \noindent #1\par }%
\a@splitht 3.5ex \a@Lunpack \putwordb@x {\ins@skip }%
\a@spacetrue \arab@codes \test@token }

\def \a@Lunpack {% unpack all lines from the insertion
\loop \a@getline \a@spacefalse 
\putwordb@x {\unhbox \tempb@x \unskip \unskip }%
\ifvbox \insertb@x \repeat }

\def \a@getline {% unpack the next line globally to \box \tempb@x
\splittopskip \a@vglue \setbox \tempb@x \vsplit \insertb@x to \a@splitht 
\setbox0 \vbox {\unvbox \tempb@x \global \setbox \tempb@x \lastbox }}

\catcode`\@ = \bidiratcode
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\endinput