[luatex] a problem with luatexUmathcode

[jfbu]

Le 13 oct. 2012 a 13:14, jfbu <jfbu at free.fr> wrote :

> 
> Le 12 oct. 2012  22:01, jfbu <jfbu at free.fr> wrote :
> 
>> Hi,  [I just posted on c.t.tex, but figured here could be better]
>> 
>> the following code gives dissimilar results for XeTeX 
>> and LuaLatex. 
>> 
>> \documentclass{article} 
>> \usepackage{ifxetex} 
>> \begin{document} 
>> \ifxetex 
>> 
>> \the\mathcode`\-           % 8704="2200 
>> \the\XeTeXmathcodenum`\-   % 37748736=2.2^{24} + 2.2^{21} + 0 
>> 
>> \else 
>> 
>> \the\mathcode`\-           % 8704 = "2200 
>> 
>> \the\luatexUmathcodenum`\- % 8704, if interpreted as Unicode 
>>                          % mathcode 0.2^{24} + 0.2^{21} + 8704 
>> \fi 
>> \end{document} 
>> 
>> This is a bit strange. The problem with this behavior of LuaLaTeX 
>> is that I need to know *in advance* if I have to interpret the 
>> number resulting from \luatexUmathcodenum as a legacy mathcode 
>> or as a Unicode mathcode ! ... 
>> 
>> best wishes, 
>> Jean-Francois
> 
> 
> Hi again
> 
> \documentclass{article} 
> \usepackage{ifxetex} 
> \begin{document} 
> \ifxetex 
> \the\XeTeXmathcodenum`\a   % 31457377 
> \the\XeTeXmathcodenum`\1   % 14680113 
> \the\XeTeXmathcodenum`\-   % 37748736 
> \else 
> \the\luatexUmathcodenum`\a   % 31457377 
> \the\luatexUmathcodenum`\1   % 28721 
> \the\luatexUmathcodenum`\-   % 8704 
> \fi 
> \end{document} 
> 
> Why the difference between querying the mathcode of a and 1?
> 
> This makes it impossible for me to use \luatexUmathcodenum to
> query the family number for 1 or -, as I can not know in advance
> if it will return a legacy mathcode (as here) or a Unicode mathcode
> (if 1 or - have been assigned Unicode mathcode).
> 
> Jean-Francois


How do I know that a package did not do something 
like \mathcode`\a="161\relax?

If this happens \the\luatexUmathcodenum`\a will be 
a legacy mathcode 353 and not a Unicode mathcode
like 31457377. The family number is not on the same
bits, and my code will be broken.

Is there some primitive (not some Lua code that I don't
want to have to learn) from Lualatex which gives me
a safe way to extract the family number of a math character?

regards

Jean-Francois