Is there a way to speed up the use of ucharclasses?

Question

The ucharclasses package is very helpful for automatic font switching based on Unicode blocks. However, it is very, very slow.

One way to speed it up is to restrict its scope on certain Unicode blocks/scripts by giving the blocks or block ranges as an option. Unfortunately, this can have negative side effects when blocks are encountered, that are not selected at package load time. (see also the discussion around my previous question here: How can I use ucharclasses to change the font for a special script and then restore to what it was before?)

Ideally, I'd like to avoid restricting ucharclasses to certain Unicode blocks and load the package without any options. Is there any way conveivable to speed up the usage of the package? Potentially by rewriting parts of the package?

Answer 1

The setup code in ucharclasses uses the awfully slow \forloop for speed critical parts of the code. Using a \loop ... \repeat construction instead is roughly 100 times faster. I agree that it is not quite as clean, but since we are talking about setting up every Unicode character, there is a lot of work to be done for each document.

Hence, it would be better if the code was

\newcommand{\@ucc@forloop}[1]
  {\expandafter\@ucc@forloop@\csname c@#1\endcsname}
\newcommand{\@ucc@forloop@}[4]{%
  #1=#2\relax
  \loop
    #4\relax
  \ifnum#1<#3\relax
    \advance#1 by \@ne
  \repeat
}
\newcounter{glyphcounter}
\newcommand{\@defineUnicodeClass}[3]{%
  \newXeTeXintercharclass#1
  \@ucc@forloop {glyphcounter}{#2}{#3}
    {\XeTeXcharclass\value{glyphcounter}=#1}
}

instead of the current definition of \@defineUnicodeClass, which is

\newcounter{glyphcounter}
\newcommand{\@defineUnicodeClass}[3]{%
  \newXeTeXintercharclass#1
  %\message{Package ucharclasses Message: #1 was assigned \the#1}
  \forloop{glyphcounter}{#2}{\value{glyphcounter}<#3}{\XeTeXcharclass\value{glyphcounter}=#1}
  \XeTeXcharclass#3=#1}

So essentially, changing the \forloop line into a faster variant would increase performance of the setup code by a sizeable factor.

However, I should warn you that the license of this package is non-free, so I am not sure whether changing your sty, even renaming it, is legal.

Answer 2

\fontspec is quite slow. If you use \setTransitionTo, use low-level font commands instead, that will be much faster.

Example:

\documentclass{article}
\usepackage[Devanagari]{ucharclasses}
\font\mangal="Mangal"
\setTransitionsFor{Devanagari}{\begingroup\mangal}{\endgroup}

\begin{document}
text and ताजा धनिया के साथ अनायास and text
\end{document}

It is much faster to use low-level font \mangal instead of \fontspec{Arial Unicode MS} or a command defined by \newfontfamily. If you use quite a lot of these transitions, it is quite clear.

However, it is not compatible with LaTeX2e's NFSS, very bad. For a better solution, see below.

---

(For advanced users)

In xeCJK, we use a font cache mechanism. Similar thing can be done: when change to a new Unicode block, cache the font by calling \fontspec and \external@font, and use the low-level command later.

Full code:

\documentclass{article}
\usepackage[Devanagari]{ucharclasses}
\usepackage{fontspec}
\newfontfamily\mangal{Mangal}

\makeatletter
% inherited from \xeCJK@setfont of xeCJK
\def\sethindifont{% Only one family here, it is simpler than xeCJK
  \ifcsname hindi@\f@series/\f@shape/\f@size\endcsname
    \@nameuse{hindi@\f@series/\f@shape/\f@size}%
  \else
    \mangal
    \get@external@font
    \expandafter\global\expandafter\font
      \csname hindi@\f@series/\f@shape/\f@size\endcsname=\external@font
  \fi}
\makeatother

% proof of code only, should have a loop
% but the code in ucharclasses have too many extra spaces
\def\ResetTransitionTo#1{%
  \XeTeXinterchartoks 255 \csname#1Class\endcsname{\relax}}

\setTransitionsFor{Devanagari}
  {\begingroup\ResetTransitionTo{Devanagari}\sethindifont}
  {\endgroup}

\begin{document}
text and ताजा धनिया के साथ अनायास and text \textbf{and ताजा धनिया के साथ अनायास and text}
\end{document}