RE: [boost] Standard Constants?

From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2000-07-08 06:56:42

I'll "boostify" if there is sufficient interest.

(Changing the names will mean they become rather long
and much less clear,
but if standards are standards, I'll go with it).

I already have some tests - and some idea about how much
the on-the-fly ones computed are different (0 to 32 epsilon!)

Paul

> -----Original Message-----
> From: jmaurer_at_[hidden]
> [mailto:jmaurer_at_[hidden]]On Behalf Of Jens Maurer
> Sent: Friday, July 07, 2000 10:06 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] Standard Constants?
> 
> 
> "Paul A. Bristow" wrote:
> > Is there any interest in some high accuracy constants for 
> the boost libraries?
> 
> Yes, I need pi in my random number library. It already has a plea
> for a "boost::mathconst" embedded in a comment.
> 
> Your suggested header file looks like it still needs some 
> boost-ification.
> boost seems to prefer all lower-case identifiers with underscores as
> separators, so it's "half_pi" instead of "halfPi".  Aliases (sqrtTwo
> and rootTwo) should be avoided.  The naming should be consistent
> (gammaThird vs. thirdPi and sqrtE vs. eSqr).  Probably define
> an explicit naming policy so that others can add further constants
> with a compatible naming.
> 
> Include guards should be applied to the header file.
> 
> Oh, and we need a test file, which would compare the constants
> to on-the-fly FPU computed values with a certain accuracy.
> 
> You should upload your package to the boost "files" section
> at www.egroups.com/files/boost in a new directory.
> 
> > typedef double real_type;  // float or double or long double.
> > // Changing this typedef automatically converts the constant to the
> > appropriate
> > // type, for example float 1.234F, double 1234. or long 
> double 1.234L.
> 
> This is plain ugly.  Use a template instead, that's exactly what they
> were made for.  Example:
> 
> template<class T>
> struct mathconst
> {
>   static const double pi;
>   // ...
> };
> template<class T> const double mathconst<T>::pi = 3.14;
> 
> I think we need pi, e and the euler constant, but the rest can
> be computed (with a possible loss of accuracy, of course).
> Probably we should offer only a basic set of constants to gain
> more experience before expanding things further.
> 
> If we ever consider physical constant, they should be in a different
> header file.
>  
> > const real_type realMax = std::numeric_limits<real_type>::max();
> > const real_type eps = std::numeric_limits<real_type>::epsilon();
> 
> This is completely redundant and should be avoided.  That would also
> do away with #include <limits> and makes the file self-contained.
> 
> > const real_type pi = (real_type) 
> 3.141592653589793238462643383279502884197;
> 
> I think the compiler is allowed to parse 3.14..., store it as 
> a "double"
> internally and convert it to a "long double" afterwards (when
> real_type == long double).  This makes all the countless digits rather
> useless.  Thus, all constants should be given as "long double", e.g.
> 3.14......L.
> 
> Please don't be disappointed by the above suggestions.  I am looking
> forward to seeing a re-worked header file.
> 
> Jens Maurer
> 
> 
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