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peter wilson <[log in to unmask]>
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Mailing list for the LaTeX3 project <[log in to unmask]>
Tue, 15 Jun 2010 20:48:42 -0400
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Joseph Wright wrote:
> Hello all,
> Those of you who take an interest in the LaTeX3 SVN may have noticed 
> that I've just added the beginnings of a 'l3fp' module as part of expl3. 
> This is intended to provide a set of floating point functions for LaTeX3.
> As you'll all know, floating point work in TeX is not exactly easy 
> (excepting when using LuaTeX, where of course the Lua route is 
> available). The aim of l3fp is to provide accurate floating point 
> functions (i.e. not using dimens) with a reasonable range of input and 
> written for speed so that the module is generally useful.
> At the moment there are only a small set of basic arithmetic functions 
> available in l3fp. So for example there is
>   \fp_add:Nnn <var> <a> <b>
> which adds <a> and <b> and assigns the result to <var>. I've also 
> defined an 'fp' data type, which is currently simply a macro which 
> contains a number. So there is also a function
>   \fp_add:Nn <var> <a>
> which adds <a> to the current content of <var> (which of course should 
> be an fp).
> In terms of input range, I've gone for -999999999.999999999 to 
> +999999999.999999999. This should be sufficient for a wide range of 
> purposes (for example, if you convert a dimen into a floating point 
> number in units pt then you are safe for any dimen TeX can handle).
> The design of the internals of the package is loosely following the 
> well-known fp package. However, that package is rather slow, at least 
> partly as it handles 18 digits either side of the decimal. The approach 
> in l3fp currently delivers addition, subtraction, multiplication and 
> division much faster than fp does (between about 8 and 15 times as fast 
> for a large number of repeated calculations). I hope this makes the 
> module fast enough for practical use.
> The next phase is to add some more complex functions. I'm planning to 
> cover trigonometry, exponential/ln and roots, plus a pseudo-random 
> number generator and a few utility functions. They may take a while: 
> getting it right is not that easy.
> Feedback on the module is very welcome, for example on which functions 
> to provide, bugs (there are bound to be some), etc.
> -- 
> Joseph Wright

     At one point, many tears (a Freudian slip --- I meant to write 
`years') ago, I needed to manipulate large numbers within LaTeX and 
wrote a package to do so. I never released it and it has gone the way of 
several computer upgrades. In any case, it handled mantissas in the 
range 0 -- 1,000,000,000 with exponents in the range of +/- 0 -- 
1,000,000,000. Would you consider extending your basic l3fp module to 
include exponents, perhaps, if necessary by being able to switch between 
the current 18 significant digits to 9 significant digits + exponent.

Peter W.