best to avoid infinite loops

[latex2e.git] / trunk / base / ltfsstrc.dtx

% \iffalse meta-comment
%
% Copyright 1993-2016
% The LaTeX3 Project and any individual authors listed elsewhere
% in this file.
%
% This file is part of the LaTeX base system.
% -------------------------------------------
%
% It may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3c
% of this license or (at your option) any later version.
% The latest version of this license is in
%    http://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions of LaTeX
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%
% This file has the LPPL maintenance status "maintained".
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% given in the file `manifest.txt'. See also `legal.txt' for additional
% information.
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% The list of derived (unpacked) files belonging to the distribution
% and covered by LPPL is defined by the unpacking scripts (with
% extension .ins) which are part of the distribution.
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% \fi
%
% \iffalse
%%% From File: ltfsstrc.dtx
%% Copyright (C) 1989-97 by Frank Mittelbach and Rainer Sch\"opf.
%% Copyright (C) 1994-97 by LaTeX3 project. All rights reserved.
%
%<package>\NeedsTeXFormat{LaTeX2e}[1995/05/16]
%<package>\ProvidesPackage{tracefnt}
%<package>     [2015/02/21 v3.0k  Standard LaTeX package (font tracing)]
% \fi
% \ProvidesFile{ltfsstrc.dtx}
%              [2015/02/21 v3.0k LaTeX Kernel (NFSS tracing)]
%
% \iffalse
%<+checkmem>\CHECKMEM
% \fi
%
%
%
%
% \changes{v3.0g}{1995/11/28}
%        {documentation fixes}
% \changes{v3.0f}{1995/10/22}{Added `genb' and `sgenb' size functions
%    to support new DC font naming scheme.}
% \changes{v3.0e}{1995/10/20}
%        {(DPC) Modify autoload code}
% \changes{v3.0d}{1995/10/04}
%        {(DPC) Modify autoload code}
% \changes{v3.0b}{1995/05/24}
%        {(DPC) Fix \cs{ProvidesFile} usage}
% \changes{v3.0a}{1995/05/24}
%        {(DPC) Make file from previous file, tracefnt 1995/05/16 v2.3o}
% \changes{v3.0k}{2015/02/21}
%         {Removed autoload code}
%
% \changes{v2.3m}{1994/11/18}
%         {\cs{next} to \cs{reserved@f}}
% \changes{v2.3l}{1994/11/17}
%         {\cs{@tempa} to \cs{reserved@a}}
% \changes{v2.3i}{1994/05/20}{Use new error command names}
% \changes{v2.3g}{1994/05/13}{Removed typeouts as
%             \cs{ProvidesPackage} writes to log.}
% \changes{v2.3e}{1994/04/27}{Corrected item that was forgotten
%                               in last change.}
% \changes{v2.3d}{1994/04/18}{Changed to new error/warning scheme}
% \changes{v2.3a}{1994/01/17}{New math font setup}
% \changes{v2.2a}{1993/11/11}{Option concept added for LaTeX2e}
% \changes{v2.1j}{1993/09/15}{Corrected spelling of \cs{noxpand}.}
% \changes{v2.1i}{1993/09/02}{Corrected name of sgen size function.}
% \changes{v2.1h}{1993/07/16}{Changed layout of info messages}
% \changes{v2.1b}{1993/03/18}
%      {Changed all \cs{@tempdimb} in \cs{@tempdimx}
%                  to avoid killing \cs{numberline}}
% \changes{v2.1b}{1993/03/18}
%      {Changed all \cs{@tempdima} in \cs{@tempdimb}
%                           to avoid killing \cs{numberline}}
% \changes{v1.0l}{1990/04/01}{Part of code moved to fam.dtx.}
% \changes{v1.0k}{1990/03/14}{Added code for TeX3.}
% \changes{v1.0h}{1990/01/18}{\cs{tracingfonts} meaning changed.}
%
% \newcommand\module[1]{\texttt{#1}}
% \providecommand{\dst}{\textsc{DocStrip}}
% \newcommand\Loption[1]{\texttt{#1}}
%
% \GetFileInfo{ltfsstrc.dtx}
% \title{The \texttt{tracefnt} package\thanks
%               {This file has version number \fileversion, dated
%                \filedate.} \\
%       for use with the new font selection scheme}
% \author{Frank Mittelbach \and Rainer Sch\"opf}
%
%
% \MaintainedByLaTeXTeam{latex}
% \maketitle
%
% \section{Introduction}
%
% This package contains the code for tracing font loading and font
% changes.  It basically overlays some of the low-level functions of
% NFSS with additional code used for tracing.
%
% The package accepts the following options:
% \begin{description}
% \item[errorshow]      Write all information about font changes etc.\
%   only to the transcript file unless an error happens. This means
%   that information about font substitution will not be shown on the
%   terminal.
%
% \item[warningshow]    Show all NFSS warnings on the terminal. This
%   setting corresponds to the default behaviour of NFSS if the
%   \texttt{tracefnt} package is \emph{not} loaded!
%
% \item[infoshow]       Show all NFSS warning and all NFSS info
%   messages (that are normally only written to the transcript file)
%   also on the terminal. This is the default if the \texttt{tracefnt}
%   package is loaded.
%
% \item[debugshow]      In addition to \texttt{infoshow} show also
%   changing of math fonts as far as possible (this option can produce a
%   large amount of output.
%
% \item[loading]        Show the name of external fonts when they are
%   loaded. This option shows only ``newly'' loaded fonts not those
%   already preloaded in the format or the class file before the
%   \texttt{tracefnt} package became active.
%
% \item[pausing]
%   Turn all font warnings into errors so that \LaTeX{} will stop.
%
% \end{description}
%
%
% \StopEventually{}
%
% \section{A driver for this document}
%
%    The next bit of code contains the documentation driver file for
%    \TeX{}, i.e., the file that will produce the documentation you
%    are currently reading. It will be extracted from this file by the
%    \dst{} program.
%
%    When this file is processed directly by \LaTeX{} this will
%    produce the documentation as well.
%
%    \begin{macrocode}
%<*driver>
\documentclass{ltxdoc}


%\OnlyDescription  % comment out for implementation details

\begin{document}
   \DocInput{ltfsstrc.dtx}
\end{document}
%</driver>
%    \end{macrocode}
%
%
% \section{The Implementation}
%
% \begin{quote}
%   \textbf{Warning:} Read the macro documentation with a grain of
%   salt. It is still basically the documentation from the first NFSS
%   release and therefore in some cases probably not completely
%   accurate.
% \end{quote}
%
% If we are making a package file it is a good idea to test whether
% we are running under 2e.
% This code is actually placed at the very beginning of this file
% for easier maintenance, thus commented out here.
%    \begin{macrocode}
%<*package>
%\NeedsTeXFormat{LaTeX2e}
%\ProvidesPackage{tracefnt}[??/??/?? v?.??
%                           Standard LaTeX package (font tracing)]
%</package>
%    \end{macrocode}
%
%
% The \texttt{debug} module makes use of commands contained in a
% special package file named \texttt{trace.sty}.\footnote{This package
% is not in distribution at the moment (and probably doesn't any
% longer work). Think of this part of the code as being historical
% artefacts.}
%    \begin{macrocode}
%<+debug> \input trace.sty
%    \end{macrocode}
%
%
% \section{Handling Options}
%
% \begin{macro}{\tracingfonts}
%    Here is the definition of the integer register for the font
%    trace.  As a default in a package file we use $1$ to give error
%    messages if fonts are substituted. If this code is used for
%    debugging or tracing reasons in the format file (i.e.\ in
%    \texttt{fam.dtx}) we use $0$ as the default.  But if no font
%    trace is used we build a definition that will produce a warning
%    message.
% \changes{v1.0l}{1990/04/01}
%      {Check if \cs{tracingfonts} already defined.}
% \changes{v1.0o}{1990/04/01}
%      {Check if \cs{tracingfonts} defined removed again.}
%    \begin{macrocode}
%<*2ekernel>
\def\tracingfonts{%
  \@font@warning{Command \noexpand\tracingfonts
           not provided.\MessageBreak
           Use the `tracefnt' package.\MessageBreak Command found:}%
       \count@}
%</2ekernel>
%    \end{macrocode}
%    The |\count@| in the line above will remove the number after
%    |\tracingfonts|. Note that this definition will be overwritten be
%    the next line if one of these modules are included.
%    \begin{macrocode}
%<*package,trace,debug>
\newcount\tracingfonts
\tracingfonts=0
%</package,trace,debug>
%    \end{macrocode}
% \end{macro}
%
%
%    The option \Loption{errorshow} turns off all warnings so that only
%    real errors are shown. \Loption{warningshow} corresponds  to the
%    NFSS default (when \texttt{tracefnt} is not loaded).
%    \Loption{infoshow} is the default for this package here; and
%    \Loption{debugshow}, \Loption{loading}, and
%    \Loption{pausing} extend the amount of information even further.
% \changes{v2.3o}{1995/05/13}
%      {Use single hash mark in \cs{DeclareOption}}
%    \begin{macrocode}
%<*package>
\DeclareOption{errorshow}{%
   \def\@font@info#1{%
         \GenericInfo{(Font)\@spaces\@spaces\@spaces\space\space}%
                     {LaTeX Font Info: \space\space\space#1}}%
    \def\@font@warning#1{%
         \GenericInfo{(Font)\@spaces\@spaces\@spaces\space\space}%
                        {LaTeX Font Warning: #1}}%
     }
%    \end{macrocode}
%
%    \begin{macrocode}
\DeclareOption{warningshow}{%
   \def\@font@info#1{%
         \GenericInfo{(Font)\@spaces\@spaces\@spaces\space\space}%
                     {LaTeX Font Info: \space\space\space#1}}%
    \def\@font@warning#1{%
         \GenericWarning{(Font)\@spaces\@spaces\@spaces\space\space}%
                        {LaTeX Font Warning: #1}}%
     }
%    \end{macrocode}
%
%    \begin{macrocode}
\DeclareOption{infoshow}{%
   \def\@font@info#1{%
         \GenericWarning{(Font)\@spaces\@spaces\@spaces\space\space}%
                     {LaTeX Font Info: \space\space\space#1}}%
    \def\@font@warning#1{%
         \GenericWarning{(Font)\@spaces\@spaces\@spaces\space\space}%
                        {LaTeX Font Warning: #1}}%
     }
%    \end{macrocode}
%
%    \begin{macrocode}
\DeclareOption{loading}{%
    \tracingfonts\tw@
   }
%    \end{macrocode}
%
%    \begin{macrocode}
\DeclareOption{debugshow}{%
    \ExecuteOptions{infoshow}%
    \tracingfonts\thr@@
   }
%    \end{macrocode}
%
% \changes{v3.0j}{1997/05/29}{Replaced \texttt{\symbol{92}\symbol{92}}
%        by \cs{MessageBreak}, as suggested by Donald Arseneau.}
%    \begin{macrocode}
\DeclareOption{pausing}{%
    \def\@font@warning#1{%
      \GenericError
             {(Font)\@spaces\@spaces\@spaces\space\space}%
             {LaTeX Font Warning: #1}%
             {See the LaTeX Companion for details.}%
             {I'll stop for every LaTeX Font Warning because
              you requested\MessageBreak the `pausing' option
              to the tracefnt package.}}%
   }
%    \end{macrocode}
%    We make |infoshow| the default, which in turn defines
%    |\font@warning| and |\font@info|.
%    \begin{macrocode}
\ExecuteOptions{infoshow}
\ProcessOptions
%</package>
%    \end{macrocode}
%
%    We also need a default definition inside the kernel:
%    \begin{macrocode}
%<*2ekernel>
\def\@font@info#1{%
         \GenericInfo{(Font)\@spaces\@spaces\@spaces\space\space}%
                     {LaTeX Font Info: \space\space\space#1}}%
\def\@font@warning#1{%
         \GenericWarning{(Font)\@spaces\@spaces\@spaces\space\space}%
                        {LaTeX Font Warning: #1}}%
%</2ekernel>
%    \end{macrocode}
%
%
% \section{Macros common to \texttt{fam.tex} and \texttt{tracefnt.sty}}
%
% In the first versions of \texttt{tracefnt.dtx} some macros of
% \texttt{fam.dtx}\footnote{This file is currently not distributed in
%     documented form. Its code is part of \texttt{ltfss.dtx}.}
% were redefined to included the extra tracing
% information. Now these macros are all defined in this file (i.e.\
% removed from \texttt{fam.dtx}) and different production versions can
% be obtained simply by specifying a different set of modules to
% include when generating \texttt{ltfss.dtx}.
%
%
%
% \subsection{General font loading}
%
%
% \begin{macro}{\extract@font}
%
%    This macro organizes the font loading.
%    It first calls |\get@external@font|
%    which will return in |\external@font| the name of the external
%    font file (the \texttt{.tfm}) as it was determined by the NFSS
%    tables.
%    \begin{macrocode}
%<*2ekernel|package>
\def\extract@font{%
   \get@external@font
%    \end{macrocode}
%    Then the external font is loaded and assigned to the font
%    identifier stored inside |\font@name|
%    (for this reason we need |\expandafter|).
%    \begin{macrocode}
   \global\expandafter\font\font@name\external@font\relax
%    \end{macrocode}
%    When tracing we typeout the internal and external font name.
%    \changes{v1.0k}{1990/03/14}{Added code for TeX3.}
%    \begin{macrocode}
%<*trace>
    \ifnum \tracingfonts >\@ne
    \@font@info{External font `\external@font'
              loaded as\MessageBreak \font@name}\fi
%</trace>
%    \end{macrocode}
%    Finally we call the corresponding ``loading action'' macros to
%    finish things. First the font is locally selected to allow the
%    use of |\font| inside the loading action macros.
%    \begin{macrocode}
    \font@name \relax
%    \end{macrocode}
%    The next two lines execute the ``loading actions'' for the
%    family and then for the individual font shape.
%    \begin{macrocode}
    \csname \f@encoding+\f@family\endcsname
    \csname\curr@fontshape\endcsname
    \relax
       }
%</2ekernel|package>
%    \end{macrocode}
%    The |\relax| at the end needs to be explained.
%    This is inserted to prevent \TeX{} from scanning too far
%    when it is executing the replacement text of the loading
%    code macros.
%    \end{macro}
%
%
%  \begin{macro}{\get@external@font}
%    This function tries to find an external font name. It will place
%    the name into the macro
%    |\external@font|. If no font is found it will return the one
%    that was defined via |\DeclareErrorFont|.
%    \begin{macrocode}
%<*2ekernel>
\def\get@external@font{%
%    \end{macrocode}
%    We don't know the external font name at the beginning.
%    \begin{macrocode}
   \let\external@font\@empty
   \edef\font@info{\expandafter\expandafter\expandafter\string
        \csname \curr@fontshape \endcsname}%
   \try@size@range
%    \end{macrocode}
%    If this failed, we'll try to substitute another size of the same
%    font.  This is done by the |\try@size@substitution| macro.  It
%    ``knows about'' |\do@extract@font|, |\font@name|, |\f@size|, and
%    so on.
%    \begin{macrocode}
   \ifx\external@font\@empty
      \try@size@substitution
      \ifx\external@font\@empty
         \@latex@error{Font \expandafter \string\font@name\space
                     not found}\@eha
         \error@fontshape
         \get@external@font
   \fi\fi
}
%</2ekernel>
%    \end{macrocode}
%  \end{macro}
%
%
% \changes{v1.0j}{1990/02/18}
%      {Redefine unprotected version \cs{p@selectfont}
%                           instead of \cs{selectfont}.}
%
%
% \begin{macro}{\selectfont}
% \changes{v1.1a}{1989/12/16}{Changed order of calls.}
% \changes{v2.3f}{1994/05/12}{Use \cs{DeclareRobustCommand}}
%    The macro |\selectfont| is called whenever a font change must
%    take place.
%    \begin{macrocode}
%<*2ekernel|package>
\DeclareRobustCommand\selectfont
        {%
%    \end{macrocode}
%    When \module{debug} is specified we actually want something like
%    `undebug'. The font selection is now stable so that using
%    |\tracingall| on some other macros will show us a lot of unwanted
%    information about font loading. Therefore we disable tracing during
%    font loading as long as |\tracingfonts| is less than $4$.
% \changes{v1.0m}{1990/04/05}
%      {Call \cs{tracingon} only if \cs{tracingfonts} greater than 3.}
% \changes{v1.0n}{1990/05/05}{\cs{tracingon} with new syntax.}
%    \begin{macrocode}
%<+debug>  \pushtracing
%<+debug>  \ifnum\tracingfonts<4 \tracingoff
%<+debug>  \else \tracingon\p@selectfont \fi
%    \end{macrocode}
%    If |\baselinestretch| was redefined by the user it will not
%    longer match its internal counterpart |\f@linespread|. If so we
%    call |\set@fontsize| to prepare |\size@update|.
%    \begin{macrocode}
    \ifx\f@linespread\baselinestretch \else
      \set@fontsize\baselinestretch\f@size\f@baselineskip \fi
%    \end{macrocode}
%    Then we generate the internal name of the font
%    by concatenating {\em family}, {\em series},
%    {\em shape}, and current {\em size},
%    with slashes as delimiters between them.
%    This is much more readable than standard
%    \LaTeX's |\twfbf|, etc.
%    We define |\font@name| globally, as always.
%    The reason for this is explained later on.
% \changes{v2.0b}{1992/07/26}{}
%    \begin{macrocode}
    \xdef\font@name{%
      \csname\curr@fontshape/\f@size\endcsname}%
%    \end{macrocode}
%    We call the macro |\pickup@font| which will load the font if
%    necessary.
%    \begin{macrocode}
    \pickup@font
%    \end{macrocode}
%    Then we select the font.
%    \begin{macrocode}
    \font@name
%    \end{macrocode}
%    If |\tracingfonts| is
%    greater than 2 we also show the font switch.
%    We do this before |\glb@settings| is called since this
%    macro might redefine |\font@name|.
% \changes{v1.0k}{1990/03/14}{Added code for TeX3.}
% \changes{v1.0i}{1990/02/16}{Changed \cs{f@size} to \cs{lcl@currsize}
%         (see fam file).}
%    \begin{macrocode}
%<*trace>
    \ifnum \tracingfonts>\tw@
      \@font@info{Switching to \font@name}\fi
%</trace>
%    \end{macrocode}
%    Finally we call |\size@update|. This macro is normally empty but
%    will contain actions (like setting the |\baselineskip|) that have
%    to be carried out when the font size, the base |\baselineskip| or
%    the |\baselinestretch| have changed.
%    \begin{macrocode}
    \size@update
%    \end{macrocode}
%    A similar function is called to handle anything related to
%    encoding updates. This one is changed from |\relax| by
%    |\fontencoding|.
% \changes{v2.3h}{1994/05/14}{Added \cs{enc@update}}
%    \begin{macrocode}
    \enc@update
%    \end{macrocode}
%    Just before ending this macro we have to pop the tracing stack
%    if it was pushed before.
%    \begin{macrocode}
%<+debug> \poptracing
    }
%    \end{macrocode}
% \end{macro}
%
%
%
%  \begin{macro}{\set@fontsize}
%    The macro |\set@fontsize| does the actual work. First it assigns
%    new values to |\f@size|, |\f@baselineskip| and |\f@linespread|.
%    \begin{macrocode}
\def\set@fontsize#1#2#3{%
    \@defaultunits\@tempdimb#2pt\relax\@nnil
    \edef\f@size{\strip@pt\@tempdimb}%
    \@defaultunits\@tempskipa#3pt\relax\@nnil
    \edef\f@baselineskip{\the\@tempskipa}%
    \edef\f@linespread{#1}%
%    \end{macrocode}
%    For backward compatibility and for later testing within
%    |\selectfont| the internal value of |\f@linespread| is passed
%    back to |\baselinestretch|.
%    \begin{macrocode}
    \let\baselinestretch\f@linespread
%    \end{macrocode}
%    Additional processing will happen within |\selectfont|. For this
%    reason the macro |\size@update| (which will be called in
%    |\selectfont|) will be defined to be:
%    \begin{macrocode}
      \def\size@update{%
%    \end{macrocode}
%    First calculate the new |\baselineskip| and also store it in
%    |normalbaselineskip|
%    \begin{macrocode}
        \baselineskip\f@baselineskip\relax
        \baselineskip\f@linespread\baselineskip
        \normalbaselineskip\baselineskip
%    \end{macrocode}
%    then to set up a new |\strutbox|
%    \begin{macrocode}
        \setbox\strutbox\hbox{%
          \vrule\@height.7\baselineskip
                \@depth.3\baselineskip
                \@width\z@}%
%    \end{macrocode}
%    We end with a bit of tracing information.
%    \begin{macrocode}
%<*trace>
   \ifnum \tracingfonts>\tw@
      \ifx\f@linespread\@empty
        \let\reserved@a\@empty
      \else
        \def\reserved@a{\f@linespread x}%
      \fi
      \@font@info{Changing size to \f@size/\reserved@a
                \f@baselineskip}%
      \aftergroup\type@restoreinfo \fi
%</trace>
%    \end{macrocode}
%    When all this is processed |\size@update| redefines itself to
%    |\relax| so that in later calls of |\selectfont| no extra code
%    will be executed.
%    \begin{macrocode}
        \let\size@update\relax}%
  }
%    \end{macrocode}
%  Instead of defining this macro internally we might speed things
%  up by placing the code into a separate macro and use |\let|!
%  \end{macro}
%
%
%  \begin{macro}{\size@update}
%    Normally this macro does nothing; it will be redefined by
%    |\set@fontsize| to initiate an update.
%    \begin{macrocode}
\let\size@update\relax
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\type@restoreinfo}
%    This macro produces some info when a font size and/or baseline
%    change will get restored.
% \changes{1.0r}{1990/08/27}{Some extra tracing info.}
%    \begin{macrocode}
%<*trace>
   \def\type@restoreinfo{%
      \ifx\f@linespread\@empty
        \let\reserved@a\@empty
      \else
        \def\reserved@a{\f@linespread x}%
      \fi
      \@font@info{Restoring size to
                \f@size/\reserved@a\f@baselineskip}}
%</trace>
%    \end{macrocode}
%  \end{macro}
%
% \begin{macro}{\glb@settings}
% \begin{macro}{\glb@currsize}
% \changes{v2.3a}{1994/01/17}{New math font setup}
% \changes{v2.3k}{1994/11/06}{New implementation}
%    The macro |\glb@settings| globally selects
%    all math fonts for the current size if necessary.
%    \begin{macrocode}
\def\glb@settings{%
%    \end{macrocode}
%    When |\glb@settings| gains control a size
%    change was requested and all previous font assignments need to
%    be replaced.
%    Therefore the old values of the fonts are no longer needed.
%    For every {\em math group\/} the new assignments are appended to
%    |\math@fonts|.
%    But this happens only if the |math@fonts| switch
%    is set to true.
%    However, we always set up the correct math sizes for script and
%    scriptscript  fonts since they may be needed even if we don't set
%    up the whole math machinery.
%
%    Here we set the math size, script size and scriptscript size.
%    If the |S@|\ldots{} macro is not defined we have to first
%    calculate the three sizes.
%    \begin{macrocode}
     \expandafter\ifx\csname S@\f@size\endcsname\relax
       \calculate@math@sizes
     \fi
%    \end{macrocode}
%    The effect of this is that |\calculate@math@sizes|
%    may or may not define the |S@|\ldots{} macro. In the
%    first case the next time the same size is requested
%    this macro is used, otherwise |\calculate@math@sizes| is
%    called again.
%    This also sets the |math@fonts| switch.
%    If it is true we must switch the math fonts.
%    \begin{macrocode}
     \csname S@\f@size\endcsname
     \ifmath@fonts
%<*trace>
       \ifnum \tracingfonts>\tw@
         \@font@info{Setting up math fonts for
                     \f@size/\f@baselineskip}\fi
%</trace>
%    \end{macrocode}
%    Inside a group we execute the macro for the current math {\em
%    version}.  This sets |\math@fonts| to a list of
%    |\textfont|\dots{} assignments.  |\getanddefine@fonts| (which may
%    be called at this point) needs the |\escapechar| parameter to be
%    set to $-1$.
%    \begin{macrocode}
       \begingroup
         \escapechar\m@ne
         \csname mv@\math@version \endcsname
%    \end{macrocode}
%    Then we set |\globaldefs| to 1 so that all following changes are
%    done globally.  The math font assignments recorded in
%    |\math@fonts| are executed and |\glb@currsize| is set equal to
%    |\f@size|.  This signals that the fonts for math in this size are
%    set up.
%    \begin{macrocode}
         \globaldefs\@ne
         \math@fonts
         \let \glb@currsize \f@size
       \endgroup
%    \end{macrocode}
%       Finally we execute any code that is supposed to happen
%       whenever the math font setup changes. This register will
%       be executed in local mode which means that everything that is
%       supposed to have any effect should be done globally inside.
%       We can't execute it within |\globaldefs\@ne| as we don't know
%       what ends up inside this register, e.g., it might contain
%       calculations which use some local registers to calculate the
%       final (global) value.
%    \begin{macrocode}
        \the\every@math@size
%    \end{macrocode}
%    Otherwise we announce that the math fonts are not set up for this
%    size.
%    \begin{macrocode}
%<*trace>
       \else
         \ifnum \tracingfonts>\tw@
           \@font@info{No math setup for
                       \f@size/\f@baselineskip}\fi
%</trace>
     \fi
}
%</2ekernel|package>
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
%
% \begin{macro}{\baselinestretch}
% \changes{v1.0o}{1990/06/24}{Moved to tracefnt.dtx.}
%    In |\selectfont| we used |\baselinestretch| as
%    a factor when assigning a value to |\baselineskip|.
%    We use 1 as a default (i.e.\ no stretch).
%    \begin{macrocode}
%<*2ekernel>
\def\baselinestretch{1}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\every@math@size}
% \changes{v1.0u fam.dtx}{1989/12/05}{Hook \cs{every@size} added.}
% \changes{v23.k}{1994/10/23}{Renamed to \cs{every@math@size}}
%    We must still define the hook |\every@math@size| we used in
%   |\glb@settings|.  We initialize it to nothing.  It is important to
%   remember that everything that goes into this hook should to global
%   updates, local changes will have weird effects.
%    \begin{macrocode}
\newtoks\every@math@size
\every@math@size={}
%</2ekernel>
%    \end{macrocode}
% \end{macro}
%
%
%
% \subsection{Math fonts setup}
%
%
% \subsubsection{Outline of algorithm for math font sizes}
%
% \TeX{} uses the the math fonts that are current when the end of a
% formula is reached. If we don't want to keep font setups local to
% every formula (which would result in an enormous overhead, we have
% to be careful not to end up with the wrong setup in case formulas
% are nested, e.g., we need to be able to handle
% \begin{verbatim}
% $ a=b+c \mbox{ \small for all $b$ and $c\in Z$}$
%\end{verbatim}
% Here the inner formulae |b| and |c\in Z| are typeset in |\small| but
% we have to return to |\normalsize| before we reach the closing |$|
% of the outer formula.
%
% This is handled in the following way:
% \begin{enumerate}
% \item At any point in the document the global variable
%   |\gbl@currsize| contains the point size for which the math fonts
%   currently are set up.
%
% \item \label{it:everymath} Whenever we start a formula we compare
%   its value with the local variable |\f@size| that describes the
%   current text font size.
%
% \item If both are the same we assume that we can use the current
%   math font setup without adjustment.
%
% \item \label{it:everymathend} If they differ we call |\gbl@settings|
%   which changes the math font setup and updates |\gbl@currsize|.
%   \begin{enumerate}
% \item If we are recursively inside another formula (|\if@inmath|) we
%      ensure that |\gbl@settings| is executed again in the outer
%      formula, so that the old setup is automatically restored.
% \item Otherwise, we set the switch |@inmath| locally to |true| so
%      that all nested formulae will be able to detect that they are
%      nested in some outer formula.
%   \end{enumerate}
% \end{enumerate}
%
%
% The above algorithm has the following features:
% \begin{itemize}
% \item For sizes which are not containing any formula no math setup
%   is done. Compared to the original algorithm of NFSS this results
%   in the following savings:
%   \begin{itemize}
%   \item No unnecessary loading of math fonts for sizes that are not
%      used to typeset any math formulae (explicit or implicit ones).
%   \item No time overhead due to unnecessary changes of the math font
%      setup on entrance and exit of the text font size.
%   \end{itemize}
%
% \item Math font setup changes for top-level formulae will survive
%   (there is no restoration after the formula) thus any following
%   formula in the same size will be directly typesetable. Compared to
%   original implementation in NFSS2
%   the new algorithm has the overhead of one test per formula
%   to see if the current math setup is valid (in the original
%   algorithm the setup was always valid, thus no test was necessary).
%
% \item In nested formulae the math font setup is restored in the
%   outer formula by a series of |\aftergroup| commands and checks.
%   Compared to the original algorithm this involves additional checks
%   ($2 \times \langle\mbox{non-math levels}\rangle$ per inner
%   formula).
% \end{itemize}
%
% \subsubsection{Code for math font size setting}
%
% \begin{macro}{\check@mathfonts}
% \changes{v2.3a}{1994/01/17}{New math font setup}
% \changes{v2.3c}{1994/01/26}{Correct trace info placement}
%    In the |\check@mathfonts| macros we implement the steps
%    \ref{it:everymath} to \ref{it:everymathend} except that instead
%     of a switch the macro |\init@restore@glb@settings| is used.
%    \begin{macrocode}
%<*2ekernel|package>
\def\check@mathfonts{%
  \ifx \glb@currsize \f@size
%<*trace>
    \ifnum \tracingfonts>\thr@@
        \@font@info{*** MATH: no change \f@size\space
         curr/global (\curr@math@size/\glb@currsize)}\fi
%</trace>
  \else
%<*trace>
    \ifnum \tracingfonts>\thr@@
        \@font@info{*** MATH: setting up \f@size\space
         curr/global (\curr@math@size/\glb@currsize)}\fi
%</trace>
     \glb@settings
     \init@restore@glb@settings
  \fi
  \let\curr@math@size\f@size
  \def\init@restore@glb@settings{\aftergroup\restglb@settings}%
}
%    \end{macrocode}
% \end{macro}
%
%
%
%
% \begin{macro}{\init@restore@glb@settings}
% \changes{v3.0i}{1996/07/26}{macro added replacing \cs{if@inmath} switch}
%    This macros does by default nothing but get redefined inside
%    |\check@mathfonts| to initiate fontsize restoring in nested
%    formulas.
%    \begin{macrocode}
%<-trace>\let\init@restore@glb@settings\relax
%<*trace>
\def\init@restore@glb@settings{%
       \ifnum \tracingfonts>\thr@@
        \@font@info{*** MATH: no resetting (not in
                    nested math)}\fi
}
%</trace>
%    \end{macrocode}
% \end{macro}
%
%
% \begin{macro}{\restglb@settings}
% \changes{v2.3a}{1994/01/17}{New math font setup}
% \changes{v2.3c}{1994/01/26}{Correct trace info placement}
%    This macro will be executed the first time after the current
%    formula.
%    \begin{macrocode}
\def\restglb@settings{%
%<*trace>
    \ifnum \tracingfonts>\thr@@
        \@font@info{*** MATH: restoring}\fi
%</trace>
      \begingroup
        \let\f@size\curr@math@size
        \ifx\glb@currsize \f@size
%<*trace>
    \ifnum \tracingfonts>\thr@@
        \@font@info{*** MATH: ... already okay (\f@size)}\fi
%</trace>
        \else
%<*trace>
    \ifnum \tracingfonts>\thr@@
        \@font@info{*** MATH: ... to \f@size}\fi
%</trace>
          \glb@settings
        \fi
      \endgroup
}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{Other code for math}
%
%
% \begin{macro}{\use@mathgroup}
% \changes{v1.2b}{1990/01/21}{Macro added to allow cleaner interface.}
% \changes{v1.2h}{1990/03/30}{Third argument removed (see
%    \cs{math@egroup}).}
%    The |\use@mathgroup| macro should be used in user
%    macros to select a math group. Depending on whether or not the
%    \texttt{margid} option is in force it has two or three arguments.
%    For this reason it should be called as the last macro.
%
%    First we test if we are inside math mode since we don't want to
%    apply a useless definition.
% \changes{v1.1a}{1989/12/16}{Usage of `\quotechar=' macro added.}
% \changes{v1.1a}{1989/12/16}{Redefinition of alphabet now simpler.}
%    \begin{macrocode}
\def\use@mathgroup#1#2{\relax\ifmmode
%    \end{macrocode}
% \changes{v1.0o}{1990/06/24}{Tracing code added.}
% \changes{v1.0q}{1990/07/07}{Group number added to tracing.}
%    \begin{macrocode}
%<*trace>
  \ifnum \tracingfonts>\tw@
    \count@#2\relax
    \@font@info{Using \noexpand\mathgroup
             (\the\count@) #2}\fi
%</trace>
%    \end{macrocode}
%    If so we first call the `=' macro (i.e.\ argument three) to set
%    up special things for the selected math group. Then we call
%    |\mathgroup| to select the group given by argument two and
%    finally we place |#1| (i.e.\ the argument of the \meta{math
%    alphabet identifier} at the end. This part of the code is
%    surrounded by two commands which behave like |\begingroup|
%    and |\endgroup| if we want \meta{math alphabet identifier}s
%    but will expand into |\@empty| if we want simply switches to
%    a new math group.
% \changes{v1.0p}{1990/06/30}{Added \cs{relax} after math group number.}
%    Since argument number $2$ may be a digit instead of a control
%    sequence we add a |\relax|.
%    Otherwise something like |\mit{1}| would switch to math group
%    $11$ (and back) instead of printing an oldstyle $\mit {1}$.
% \changes{v2.0b}{1992/07/26}{}
%    \begin{macrocode}
     \math@bgroup
         \expandafter\ifx\csname M@\f@encoding\endcsname#1\else
         #1\fi
         \mathgroup#2\relax
%    \end{macrocode}
%    Before we reinsert the swallowed token (arg.\ three) into the
%    input stream, in the case that the \meta{math alphabet
%    identifier} isn't called in math mode, we remove the |\fi|
%    with the |\expandafter| trick.  This is necessary if the
%    token is actually an macro with arguments. In such a case the
%    |\fi| will be misinterpreted as the first argument which
%    would be disastrous.
% \changes{v1.0f}{1989/12/13}
%      {\cs{expandafter} added before final \cs{fi}.}
%    \begin{macrocode}
     \expandafter\math@egroup\fi}%
%    \end{macrocode}
%    The surrounding macros equal |\begingroup| and |\endgroup|.  But
%    using internal names makes it possible to overwrite their meaning
%    in certain cases. This is for example used in \AmSTeX{} macros
%    for placing accents.
% \end{macro}
%
% \begin{macro}{\math@egroup}
% \changes{v1.0q}{1990/07/07}{Tracing code added.} If the
%    \texttt{margid} option is in force (which can be tested by
%    looking at the definition of |\math@bgroup| we change the
%    |\math@egroup| command a bit to display the current \meta{math
%    group number} after it closes the scope of \meta{math alphabet}
%    with |\endgroup|.
% \changes{v3.0h}{1996/05/08}{Use \cs{bgroup} instead of \cs{begingroup}
%    to match a kernel change made in 1994!!!!}
%    \begin{macrocode}
%<*trace>
  \ifx\math@bgroup\bgroup
    \def\math@egroup#1{#1\egroup
      \ifnum \tracingfonts>\tw@
     \@font@info{Restoring \noexpand\mathgroup
        (\ifnum\mathgroup=\m@ne default\else \the\mathgroup \fi)%
        }\fi}
  \fi
%</trace>
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\getanddefine@fonts}
% \changes{v1.0o}{1990/06/24}{\cs{Macro} moved from fam.dtx.}
%    |\getanddefine@fonts| has two arguments: the \meta{math
%    group number} and the {\em family/series/shape\/} name as a
%    control sequence.
%    \begin{macrocode}
\def\getanddefine@fonts#1#2{%
%    \end{macrocode}
%    First we turn of tracing when |\tracingfonts| is less than $4$.
% \changes{v1.0o}{1990/06/24}{Adding debug code.}
% \changes{v1.0r}{1990/08/27}
%      {Correcting missing name after \cs{tracingon}.}
%    \begin{macrocode}
%<+debug>  \pushtracing
%<+debug>  \ifnum\tracingfonts<4 \tracingoff
%<+debug>  \else \tracingon\getanddefine@fonts \fi
%    \end{macrocode}
% \changes{v1.0o}{1990/06/24}{\cs{Adding} tracing code.}
% \changes{v1.0q}{1990/07/07}{Group number added to tracing.}
% \changes{v2.1a}{1992/09/22}{Introduced \cs{tf@size} for math size.}
%    \begin{macrocode}
%<*trace>
  \ifnum \tracingfonts>\tw@
  \count@#1\relax
    \@font@info{\noexpand\mathgroup (\the\count@) #1 :=\MessageBreak
              \string#2 \tf@size/\sf@size/\ssf@size}\fi
%</trace>
%    \end{macrocode}
%    We append the current |\tf@size| to |#2| to obtain the font
%    name.\footnote{One might ask why this expansion does not generate
%    a macro name that starts with an additional \texttt{\bslash}
%    character.  The solution is that \texttt{\bslash escapechar} is
%    set to $-1$ before \texttt{\bslash getanddefine@fonts} is
%    called.} Again, |font@name| is defined globally, for the reasons
%    explained in the description of |\wrong@fontshape|.
%    \begin{macrocode}
  \xdef\font@name{\csname \string#2/\tf@size\endcsname}%
%    \end{macrocode}
%    Then we call |\pickup@font| to load it if necessary.
%    We remember the internal name as |\textfont@name|.
%    \begin{macrocode}
  \pickup@font \let\textfont@name\font@name
%    \end{macrocode}
%    Same game for |\scriptfont| and |\scriptscriptfont|:
%    \begin{macrocode}
  \xdef\font@name{\csname \string#2/\sf@size\endcsname}%
  \pickup@font \let\scriptfont@name\font@name
  \xdef\font@name{\csname \string#2/\ssf@size\endcsname}%
  \pickup@font
%    \end{macrocode}
%    Then we append the new |\textfont|\ldots{} assignments to
%    the |\math@fonts|.
%    \begin{macrocode}
  \edef\math@fonts{\math@fonts
               \textfont#1\textfont@name
               \scriptfont#1\scriptfont@name
               \scriptscriptfont#1\font@name}%
%    \end{macrocode}
%    Just before ending this macro we have to pop the tracing stack
%    if it was pushed before.
%    \begin{macrocode}
%<+debug> \poptracing
    }
%</2ekernel|package>
%    \end{macrocode}
% \end{macro}
%
%
% \section{Scaled font extraction}
%
%  \begin{macro}{\ifnot@nil}
%    We begin with a simple auxiliary macro. It checks
%    whether its argument is the token |\@nil|. If so,
%    it expands to |\@gobble| which discards the following
%    argument, otherwise it expands to |\@firstofone| which
%    reproduces it argument.
% \changes{v2.3n}{1995/05/08}{Use \cs{@firstofone}}
%    \begin{macrocode}
%<*2ekernel>
\def\ifnot@nil#1{\def\reserved@a{#1}%
  \ifx\reserved@a\@nnil \expandafter\@gobble
  \else \expandafter\@firstofone\fi}
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\remove@to@nnil}
%  \begin{macro}{\remove@angles}
%  \begin{macro}{\remove@star}
%    Three other auxiliary macros will be needed in the following:
%    |\remove@to@nnil| gobbles up everything up to, and including,
%    the next |\@nnil| token, and |\remove@angles| and |\remove@star|
%    do the same
%    for the character |>| and |*|, respectively, instead of |\@nnil|.
%    \begin{macrocode}
\def\remove@to@nnil#1\@nnil{}
\def\remove@angles#1>{\set@simple@size@args}
\def\remove@star#1*{#1}
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%  \end{macro}
% \changes{v3.0c}{1995/08/24}{Macro \cs{gobble@font@spec} removed}
%
%  \begin{macro}{\extract@sizefn}
%    This macro takes a size specification and parses it into size
%    function and the optional and mandatory arguments.
%    \begin{macrocode}
\def\extract@sizefn#1*#2\@nil{%
  \if>#2>\set@size@funct@args#1\@nil
         \let\sizefn@info\@empty
  \else\expandafter\set@size@funct@args\remove@star#2\@nil
       \def\sizefn@info{#1}\fi
  }
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\try@simple@size}
%    This function tries to extract the given size (specified by
%    |\f@size|) for the requested font shape. The font information
%    must already be present in |\font@info|.
%    The central macro that does the real work is |\extract@fontinfo|.
%    We will first give a simple example how this macro works, and
%    describe it in full generality later.
%
%    Assume that the requested parameters are: {\em encoding scheme\/}
%    `OT1', {\em family\/} `cm', {\em series\/} `sansserif',
%    {\em shape\/} `normal', and {\em size\/} `$12$'.
%    The corresponding font definitions have already been
%    extracted from the macro |\OT1/cm/sansserif/normal| and
%    stored in |font@info|.
%    (Otherwise |\extract@fontinfo| doesn't get called.)
%    This information consists of a token list made of characters
%    of category code $12$ of the form
%    \begin{verbatim}
%       <10*>cmss10<12*>cmss12<17*>cmss17
%\end{verbatim}
%    For reasonable packages one usually needs more sizes but this is
%    sufficient to get the flavour.
%    We will define a macro |\extract@fontinfo| to find
%    the external font name (`cmss12') for us:
%    \begin{verbatim}
%      \def\extract@fontinfo#1<12*#2>#3<#4\@nnil{%
%          \set@simple@size@args#3<#4\@nnil
%          \execute@size@function{#2}}
%\end{verbatim}
%    so that when it gets called via
%    \begin{verbatim}
%      \extract@fontinfo<10*>cmss10<12*>cmss12<17*>cmss17\@nnil
%\end{verbatim}
%    |#1| will contain all characters before |<12*>|,
%    |#2| will be empty, |#3| will be exactly |cmss12|,
%    and |#3| will be |17>cmss17|.
%    The expansion is therefore
%    \begin{verbatim}
%      \set@simple@size@args cmss12<17*>cmss17\@nnil
%      \execute@size@function{}
%\end{verbatim}
%    This means: the default (empty) size function will be executed,
%    with its optional argument argument set to empty and its mandatory
%    argument set to |cmss12| by |\set@simple@size@args|.
%    As we discussed earlier, the effect of the default size function
%    is to load the given external font (cmss12) at the specified size
%    (12)---which is exactly what was intended.
%
%    But this is only part of the whole story.
%    It may be that the size requested does not occur
%    in the token list |\font@info|.
%    And the simple definition of |\extract@fontinfo| we gave
%    above does not allow to specify give more than one
%    size specification in front of the external font name.
%
%    Let's address these two problems separately. The first one
%    is solved with the following trick:
%    We define |\extract@fontinfo| as follows:
%    \begin{verbatim}
%      \def\extract@fontinfo#1<12*#2>#3<#4\@nnil{%
%        \ifnot@nil{#3}%
%          {\set@simple@size@args#3<#4\@nnil
%           \execute@size@function{#2}%
%          }}%
%\end{verbatim}
%    How does this work?
%    We call |\extract@fontinfo| via
%    \begin{verbatim}
%      \expandafter\extract@fontinfo\font@info<12*>\@nil<\@nnil
%\end{verbatim}
%    i.e. by appending |<12*>\@nil<\@nnil|.
%    If the size (`12' in this case) appears in |\font@info|
%    everything works as explained above, the only difference being
%    that argument |#4| of |\extract@fontinfo|
%    additionally gets the tokens |<12*>\@nil<\@nnil|.
%    However, if the size is not found everything up to the final
%    |<12*>| is in argument |#1|,
%    |#3| gets |\@nil|,
%    and |#2| and |#4| are empty.
%    The macro |\ifnot@nil| will discard the calls to
%    |\set@simple@size@args| and |execute@size@function|, and
%    hence |\font@info| will continue to be equal to |\@empty|.
%    This means that no simple size specification matching the
%    requested size could be found.
%
%    The second problem (more than one simple size specification
%    for one external font name) will be addressed in
%    |\set@simple@size@args| below.
%
%    The macros are hidden inside other control sequences
%    so that we have to build |\extract@fontinfo| in
%    several steps.
%
%    So here's the actual definition of |\extract@font| in
%    |\try@simple@size|.
%    \begin{macrocode}
% % this could be replaced by \try@size@range making the subst slower!
\def\try@simple@size{%
%    \end{macrocode}
%    |\reserved@a| is made an abbreviation for the head of the
%    definition of the macro  |\extract@fontinfo|.
%    \begin{macrocode}
    \def\reserved@a{\def\extract@fontinfo####1}%
%    \end{macrocode}
%    Now we can define |\extract@fontinfo|. Here we handle a small
%    but convenient variation: in case of the default (empty) size
%    function it is allowed to omit the |*| character.
% \changes{v2.0b}{1992/07/26}{}
% \changes{v2.0c}{1992/09/19}{}
%    \begin{macrocode}
    \expandafter\reserved@a\expandafter<\f@size>##2<##3\@nnil{%
          \ifnot@nil{##2}%
            {\set@simple@size@args##2<##3\@nnil
             \execute@size@function\sizefn@info
            }}%
%    \end{macrocode}
% \changes{v2.0b}{1992/07/26}{}
%    Now we call |\extract@fontinfo|.  Note the |<\@nil| \textsf{tokens}
%    at the end.
%    \begin{macrocode}
    \expandafter\expandafter
    \expandafter\extract@fontinfo\expandafter\font@info
    \expandafter<\f@size>\@nil<\@nnil
}
%    \end{macrocode}
%  \end{macro}
%
%  \begin{macro}{\set@simple@size@args}
%    As promised above, the macro |\set@simple@size@args| will handle
%    the case of several size specifications in a row.
%    If another size specification follows, the very first token of
%    its argument list is the character |<|.
%    By starting the definition as follows,
%    \begin{macrocode}
\def\set@simple@size@args#1<{%
%    \end{macrocode}
%    parameter |#1| is empty in this case, and contains the size
%    function's arguments otherwise. We distinguish these two cases
%    (Note that the character |<| cannot appear in |#1|) by calling
%    |\remove@angles| for empty |#1| and |\extract@sizefn|
%    otherwise. In the latter case we have to take care of the
%    remaining character tokens and discard them. This is done by
%    |\remove@to@nnil|. Note also the use of Kabelschacht's method.
%    \begin{macrocode}
          \if<#1<%
            \expandafter\remove@angles
          \else
            \extract@sizefn#1*\@nil
            \expandafter\remove@to@nnil
          \fi}
%    \end{macrocode}
%  \end{macro}
%
%
%  Now, we are through with the case of a simple size, except for
%  calling the size function. This will be handled later, as it is
%  the same mechanism for all types of size specification. We will
%  now proceed to macors for extraction of size range specification.
%
%
%
%  \begin{macro}{\extract@rangefontinfo}
%    |\extract@rangefontinfo| goes through a font shape definition
%    in the input until it recognizes the tokens |<\@nil->|.
%    It looks for font ranges with font size functions. It's operation
%    is rather simple: it discards everything up to the next size
%    specification and passes this on to |\is@range| for inspection.
%    The specification (parameter |#2| is inserted again, in case
%    it is needed later.
%    \begin{macrocode}
\def\extract@rangefontinfo#1<#2>{%
       \is@range#2->\@nil#2>}
%    \end{macrocode}
%  \end{macro}
%
%  \begin{macro}{\is@range}
%    |\is@range| is again a sort of dispatcher macro: if the size
%    specification it is looking at is not a range specification
%    it discards it and calls |\extract@rangefontinfo| to continue
%    the search. Otherwise it calls |\check@range| to check the
%    requested size against the specified range.
%
%    From the way |\is@range| is called inside |\extract@rangefontinfo|
%    we see that |#2| is the character |>| if the size specification
%    found is a simple one (as it does not contain a |-| character.
%    This is checked easily enough and |\extract@rangefontinfo|
%    called again. Note that the extra tokens inserted after the
%    |\@nil| in the call to |\is@range| appear at the beginning of
%    the first argument to |\extract@rangefontinfo| and are hence
%    ignored.
%    \begin{macrocode}
\def\is@range#1-#2\@nil{%
   \if>#2\expandafter\check@single\else
      \expandafter\check@range\fi}
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\check@range}
%    |\check@range| takes lower bound as parameter |#1|, upper bound
%    as |#2|, size function as |#3| and the size function's arguments
%    as |#4|. If |#3| is the special token |\@nil| |\font@info| is
%    exhausted and we can stop searching.
%    \begin{macrocode}
\def\check@range#1-#2>#3<#4\@nnil{%
  \ifnot@nil{#3}{%
%    \end{macrocode}
%    If |#3| wasn't |\@nil| we have a range. We start by assuming that
%    we have to recurse. Note that we have to reinsert an |<| as it
%    was already removed by scanning.
%    \begin{macrocode}
     \def\reserved@f{\extract@rangefontinfo<#4\@nnil}%
%    \end{macrocode}
%    We have to make sure that both boundaries are present, if not we
%    have to set them.  Here we check the upper bound. If |\upper@bound|
%    is zero after the assignment we set it to |\maxdimen| (upper open
%    range). We need to use a \meta{dimen} register for the scan since
%    we may have a decimal number as the boundary.
%    \begin{macrocode}
     \upper@bound0#2\p@
     \ifdim\upper@bound=\z@ \upper@bound\maxdimen\fi
%    \end{macrocode}
%    Now we check the upper boundary against |\f@size|.
%    If it is larger or equal than |\f@size| this
%    range is no good and we have to recurse.
%    \begin{macrocode}
     \ifdim \f@size \p@<\upper@bound
%    \end{macrocode}
%    Otherwise we have to check the lower bound. This time it is not
%    necessary to scan the boundary value into a register because if
%    it is empty we get zero as desired. We could even omit the |0|
%    which would result in |1pt| as default lower boundary. If
%    |\f@size| is smaller than the boundary we have to recurse.
%    \begin{macrocode}
       \lower@bound0#1\p@
       \ifdim \f@size \p@<\lower@bound
        \else
%    \end{macrocode}
%    If both tests are passed we can try executing the size function.
%    \begin{macrocode}
          \set@simple@size@args#3<#4\@nnil
          \execute@size@function\sizefn@info
%    \end{macrocode}
%    If the function was successful it should have left an external
%    font name in |\external@font|. We use this to see if we can stop
%    scanning. Otherwise we recurse.
%    \begin{macrocode}
         \ifx\external@font\@empty
         \else
           \let\reserved@f\@empty
         \fi
       \fi
     \fi
     \reserved@f}}
%    \end{macrocode}
%  \end{macro}
%
%  \begin{macro}{\lower@bound}
%  \begin{macro}{\upper@bound}
%    We use two dimen registers |\lower@bound| and |\upper@bound|
%    to store the lower and upper endpoints of the range we found.
%    \begin{macrocode}
\newdimen\lower@bound
\newdimen\upper@bound
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%
%
%  \begin{macro}{\check@single}
%    |\check@single| takes the size as parameter |#1|, size function
%    as |#2| and the size function's arguments as |#3|. We can assume
%    that there is always something in the pipeline since the very
%    last entry is a faked range (see above).
%    \begin{macrocode}
\def\check@single#1>#2<#3\@nnil{%
%    \end{macrocode}
%    We start by assuming that
%    we have to recurse. Note that we have to reinsert an |<| as it
%    was already removed by scanning.
%    \begin{macrocode}
     \def\reserved@f{\extract@rangefontinfo<#3\@nnil}%
%    \end{macrocode}
%    Now we check the the size against |\f@size|.  If it is not equal
%    |\f@size| it is no good and we have to recurse.
%    \begin{macrocode}
     \ifdim \f@size \p@=#1\p@
%    \end{macrocode}
%    Otherwise if this test is passed we can try executing the size
%    function.
%    \begin{macrocode}
        \set@simple@size@args#2<#3\@nnil
        \execute@size@function\sizefn@info
%    \end{macrocode}
%    If the function was successful it should have left an external
%    font name in |\external@font|. We use this to see if we can stop
%    scanning. Otherwise we recurse.
%    \begin{macrocode}
        \ifx\external@font\@empty
        \else
          \let\reserved@f\@empty
        \fi
     \fi
     \reserved@f}
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\set@size@funct@args}
%  \begin{macro}{\set@size@funct@args@}
%    This macro sets the optional and mandatory arguments for a size
%    function. If the optional argument is not present it is set to
%    the empty token list. The mandatory argument is delimited by the
%    token |\@nil|.
%    \begin{macrocode}
\def\set@size@funct@args{\@ifnextchar[%
  \set@size@funct@args@{\set@size@funct@args@[]}}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\set@size@funct@args@[#1]#2\@nil{%
  \def\mandatory@arg{#2}%
  \def\optional@arg{#1}}
%</2ekernel>
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%
%
%  \begin{macro}{\DeclareSizeFunction}
%    This function defines a new size function hiding the internal
%    from the designer. The body of the size function may use
%    |\optional@arg| and |\mandatory@arg| denoting the optional and
%    mandatory argument that may follow the size specification |<...>|.
% \changes{v2.1c}{1993/03/18}{Added all args to avoid blanks problems}
%    \begin{macrocode}
%<*2ekernel>
\def\DeclareSizeFunction#1#2{\@namedef{s@fct@#1}{#2}}
\@onlypreamble\DeclareSizeFunction
%</2ekernel>
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\execute@size@function}
%    This macro is very simple. The only point worth noting
%    is that calling an undefined size function will do nothing
%    (actually execute a |\relax|).
%    \begin{macrocode}
%<*2ekernel|package>
\def\execute@size@function#1{%
%<*trace>
         \@ifundefined{s@fct@#1}%
           {\errmessage{Undefined font size function #1}%
            \s@fct@}%
           {\csname s@fct@#1\endcsname}%
%</trace>
%<-trace>      \csname s@fct@#1\endcsname
}
%</2ekernel|package>
%    \end{macrocode}
%  \end{macro}
%
% \changes{v2.3j}{1994/05/23}{Removed def of \cs{f@warn@break}}
%
%
%  \begin{macro}{\try@size@range}
%    This macro tries to find a suitable range for requested size
%    (specified by |\f@size|) in |\font@info|. All the relevant
%    action is done in |\extract@rangefontinfo|. All that needs
%    to be done is to stuff in the token list in |\font@info| so
%    that |\extract@rangefontinfo| can inspect it.
%    Note the |<-*\@nil><| token at the end to stop scanning.
% \changes{v2.0b}{1992/07/26}{}
%    \begin{macrocode}
%<*2ekernel>
\def\try@size@range{%
    \expandafter\extract@rangefontinfo\font@info <-*>\@nil<\@nnil
}
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\try@size@substitution}
% \changes{v2.3k}{1994/11/06}{New implementation}
%    This is the last thing that can be tried. If the desired |\f@size|
%    is found neither among the simple size specifications nor in one
%    of the ranges the whole list of size specifications is searched for
%    a nearby simple size.
%    \begin{macrocode}
\gdef\try@size@substitution{%
%    \end{macrocode}
%    First we do some initializations. |\@tempdimb|
%    will hold the difference between the wanted size and the best
%    solution found so far, so we initialise it with |\maxdimen|.
%    The macro |\best@size| will hold the best size found, nothing
%    found is indicated by the empty value.
%    \begin{macrocode}
  \@tempdimb \maxdimen
  \let \best@size \@empty
%    \end{macrocode}
%    Now we loop over the specification
%    \begin{macrocode}
  \expandafter \try@simples \font@info <\number\@M>\@nil<\@nnil
}
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\font@submax}
% \changes{v2.3d}{1994/04/18}{Changed dimen to macro}
%  \begin{macro}{\fontsubfuzz}
% \changes{v2.3d}{1994/04/18}{Changed dimen to macro}
%    The macro |\font@submax| records the maximal deviation from the
%    desired size encountered so far. Its value is used in a warning
%     message at |\end{document}|. The macro
%    |\fontsubfuzz| contains the amount that will not cause terminal
%    warnings (warnings still go into the transcript file).
%    \begin{macrocode}
\def\font@submax{0pt}
\def\fontsubfuzz{.4pt}
%</2ekernel>
%<+package>\def\fontsubfuzz{0pt}
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%
%
%
%  \begin{macro}{\try@simples}
% \changes{v2.3k}{1994/11/06}{New implementation}
%    |\try@simples| goes through a font shape definition
%    in the input until it recognizes the tokens |<*\@nil><|.
%    It looks for simple sizes to determine the two closest sizes.
%    It is assumed that simple sizes are in increasing order.
%    \begin{macrocode}
%<*2ekernel>
\gdef\try@simples#1<#2>{%
  \tryif@simple#2->\tryif@simple}
%    \end{macrocode}
%  \end{macro}
%
%  \begin{macro}{\tryis@simple}
% \changes{v2.3k}{1994/11/06}{New implementation}
%   |\tryis@simple| is similar to |\is@range|. If it sees a simple size,
%   it checks it against the value of |\f@size| and sets
%   |\lower@font@size| or |\higher@font@size|. In the latter case, it
%   stops the iteration. By adding |<\number\@M>| at the end of the
%   line we always have an end point. This is a hack which probably
%   should be corrected.
%
%    First it checks whether it is finished already, then whether the
%    size specification in question is a simple one.
%    \begin{macrocode}
\gdef\tryif@simple#1-#2\tryif@simple{%
%    \end{macrocode}
%    Most common case for |\reserved@f| first:
%    \begin{macrocode}
  \let \reserved@f \try@simples
  \if>#2%
%    \end{macrocode}
%    If so, it compares it to the value of |\f@size|. This is done using
%    a dimen register since there may be fractional numbers.
%    \begin{macrocode}
    \dimen@ #1\p@
    \ifdim \dimen@<\@M\p@
%    \end{macrocode}
%    If |\dimen@| is |\@M\p@| we have reached the end of the fontspec
%    (hopefully) otherwise we compare the value with |\f@size| and
%    compute in |\@tempdimc| the absolute value of the difference
%    between the two values.
%    \begin{macrocode}
      \ifdim \f@size\p@<\dimen@
        \@tempdimc \dimen@
        \advance\@tempdimc -\f@size\p@
      \else
        \@tempdimc \f@size\p@
        \advance\@tempdimc -\dimen@
      \fi
%    \end{macrocode}
%    The result is then compared with the smallest difference we have
%    encountered, if the new value (in |\@tempdimc| is smaller) we
%    have found a size which is a better approximation so we make it
%    the |\best@size| and adjust |\@tempdimb|.
%    \begin{macrocode}
      \ifdim \@tempdimc<\@tempdimb
        \@tempdimb \@tempdimc
        \def \best@size{#1}%
      \fi
%    \end{macrocode}
%    When we have reached the end of the fontspec we substitute the
%    best size found (if any). We code this inline to save macro
%    space; in the past this was done by a macro called |\subst@size|.
%    \begin{macrocode}
    \else
%    \end{macrocode}
%
%
%  \begin{macro}{\subst@size}
%    This macro substitutes the size recorded in |\best@size| for
%    the unavailable size |\f@size|. |\font@submax| records the maximum
%    difference between desired size and selected size in the
%    whole run.
% \changes{v2.3d}{1994/04/18}{\cs{font@submax} and \cs{fontsubfuzz}
%                             now macros}
%    \begin{macrocode}
% %\subst@size             %% coded inline
% %\def\subst@size{%
  \ifx \external@font\@empty
    \ifx \best@size\@empty
    \else
      \ifdim \@tempdimb>\font@submax \relax
        \xdef \font@submax {\the\@tempdimb}%
      \fi
      \let \f@user@size \f@size
      \let \f@size \best@size
      \ifdim \@tempdimb>\fontsubfuzz\relax
        \@font@warning{Font\space shape\space
            `\curr@fontshape'\space in\space size\space
             <\f@user@size>\space not\space available\MessageBreak
             size\space <\f@size>\space substituted}%
      \fi
      \try@simple@size
      \do@subst@correction
    \fi
 \fi
% %}
%    \end{macrocode}
%  \end{macro}
%
%    This brings us back into the main part of |\tryif@simple|.
%    Finally we get rid of any rubbish left over on the input stack.
%
% \changes{v3.0c}{1995/08/24}{}
%    \begin{macrocode}
      \let \reserved@f \remove@to@nnil
    \fi
  \fi
%    \end{macrocode}
%    If it's a range iterate also.
%    \begin{macrocode}
  \reserved@f}
%    \end{macrocode}
%  \end{macro}
%
%
%
% \subsection{Sizefunctions}
%
%  In the following we define some useful size functions.
%
%
%  \begin{macro}{\s@fct@}
%    This is the default size function. Mandatory argument is an
%    external font name, optional argument a scale factor.
%    The font is scaled
%    to |\f@size| if no optional argument is present, and to
%    |\f@size| multiplied by the optional argument otherwise.
% \changes{v2.0b}{1992/07/26}{}
%    \begin{macrocode}
\DeclareSizeFunction{}{\empty@sfcnt\@font@warning}
\DeclareSizeFunction{s}{\empty@sfcnt\@font@info}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\empty@sfcnt#1{%
      \@tempdimb \f@size\p@
      \ifx\optional@arg\@empty
      \else
        \@tempdimb \optional@arg\@tempdimb
        #1{Font\space shape\space `\curr@fontshape'\space
           will\space be\MessageBreak
           scaled\space to\space size\space \the\@tempdimb}%
      \fi
      \edef\external@font{\mandatory@arg\space at\the\@tempdimb}}
%    \end{macrocode}
%  \end{macro}
%
%
%
%  \begin{macro}{\s@fct@gen}
%  \begin{macro}{\s@fct@sgen}
%    This size function generates the external name from the mandatory
%    argument and the requested user size, and thus can be used for
%    external names where the size is encoded in the font name. The
%    optional argument a scale factor.  The font is scaled to |\f@size|
%    if no optional argument is present, and to |\f@size| multiplied
%    by the optional argument otherwise.
%    \begin{macrocode}
\DeclareSizeFunction{gen}{\gen@sfcnt\@font@warning}
\DeclareSizeFunction{sgen}{\gen@sfcnt\@font@info}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\gen@sfcnt{%
      \edef\mandatory@arg{\mandatory@arg\f@size}%
      \empty@sfcnt}
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%
%
%
%  \begin{macro}{\s@fct@genb}
%  \begin{macro}{\s@fct@sgenb}
%    This size function is similar to |gen|, but for fonts where the
%    size is encoded in the font name in centipoints, as in the DC
%    fonts version 1.2.  The font is scaled to |\f@size|
%    if no optional argument is present, and to |\f@size| multiplied
%    by the optional argument otherwise.
%    \begin{macrocode}
\DeclareSizeFunction{genb}{\genb@sfcnt\@font@warning}
\DeclareSizeFunction{sgenb}{\genb@sfcnt\@font@info}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\genb@sfcnt{%
    \edef\mandatory@arg{\mandatory@arg\expandafter\genb@x\f@size..\@@}%
    \empty@sfcnt}
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%
%
%  \begin{macro}{\genb@x}
%  \begin{macro}{\genb@y}
%    The auxiliary macros |\genb@x| and |\genb@y| are used to convert
%    the |\f@size| into centipoints.
%    \begin{macrocode}
\def\genb@x#1.#2.#3\@@{\two@digits{#1}\genb@y#200\@@}
\def\genb@y#1#2#3\@@{#1#2}
%    \end{macrocode}
%  \end{macro}
%  \end{macro}
%
%
%
%  \begin{macro}{\s@fct@sub}
%    This size function handles font substitution.
%    The mandatory argument is a family/series/shape combination,
%    the optional argument (if present) is ignored. The font encoding
%    scheme cannot be changed. Therefore, the first thing we do is to
%    prepend the encoding scheme.
% \changes{v2.0b}{1992/07/26}{}
%    \begin{macrocode}
\DeclareSizeFunction{sub}{\sub@sfcnt\@font@warning}
\DeclareSizeFunction{ssub}{\sub@sfcnt\@font@info}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\sub@sfcnt#1{%
    \edef\mandatory@arg{\f@encoding/\mandatory@arg}%
%    \end{macrocode}
%    Next action is split the arg into its individual components and
%    allow for a late font shape load.
%    \begin{macrocode}
    \begingroup
     \expandafter\split@name\mandatory@arg/\@nil
     \try@load@fontshape
    \endgroup
%    \end{macrocode}
%    Then we record the current |\f@size| since it may get clobbered.
%    \begin{macrocode}
    \let\f@user@size\f@size
%    \end{macrocode}
%    Then we check whether this new combination is defined and
%    give an error message if not. In this case we also switch to
%    |\error@fontshape|.
%    \begin{macrocode}
    \expandafter
    \ifx\csname\mandatory@arg\endcsname\relax
      \errmessage{No\space declaration\space for\space
                  shape\space \mandatory@arg}%
      \error@fontshape
    \else
%    \end{macrocode}
%    Otherwise we warn the user about the substitution taking place.
%    \begin{macrocode}
      #1{Font\space shape\space `\curr@fontshape'\space in\space
         size\space <\f@size>\space not\space available\MessageBreak
         Font\space shape\space `\mandatory@arg'\space tried\space
         instead}%
      \expandafter\split@name\mandatory@arg/\@nil
    \fi
%    \end{macrocode}
%    Then we restart the font specification scan by calling
%    |\get@external@font|.
%    \begin{macrocode}
    \edef\f@size{\f@user@size}%
    \get@external@font
%    \end{macrocode}
%    Finally |\do@subst@correction| is called to get the font name
%    right.
%    \begin{macrocode}
    \do@subst@correction
}
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\s@fct@subf}
%    The |subf| size function allows substitution of another font. The
%    mandatory argument is the external name of the font to be
%    substituted, the optional argument a size scaling factor like
%    in the default size function.
%    The main difference to the default size function is the warning
%    message.
%    \begin{macrocode}
\DeclareSizeFunction{subf}{\subf@sfcnt\@font@warning}
\DeclareSizeFunction{ssubf}{\subf@sfcnt\@font@info}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\subf@sfcnt#1{%
      #1{Font\space shape\space `\curr@fontshape'\space in\space
         size\space \f@size\space not\space available\MessageBreak
        external\space font\space `\mandatory@arg'\space used}%
      \empty@sfcnt#1%
      }
%    \end{macrocode}
%  \end{macro}
%
%
%  \begin{macro}{\s@fct@fixed}
%    The |fixed| size function is for using a font at a different size
%    than requested. A warning message is printed, and the external
%    font to be used is taken from the mandatory argument.
%    If an optional argument is present it is used as the `at'
%    size for the font. Otherwise the font is loaded at its design size.
%    \begin{macrocode}
\DeclareSizeFunction{fixed}{\fixed@sfcnt\@font@warning}
\DeclareSizeFunction{sfixed}{\fixed@sfcnt\@font@info}
%    \end{macrocode}
%
%    \begin{macrocode}
\def\fixed@sfcnt#1{%
  \ifx\optional@arg\@empty
    \let\external@font\mandatory@arg
  \else
    \edef\external@font{\mandatory@arg\space at\optional@arg pt}%
  \fi
  #1{External\space font\space `\external@font'\space loaded\space
     for\space size\MessageBreak
     <\f@size>}%
}
%</2ekernel>
%    \end{macrocode}
%  \end{macro}
%
% \iffalse
%<+checkmem>\CHECKMEM
% \fi
%
%
% \Finale