RE: [boost] RE: math constant - generic function circle_area example.

From: Paul A. Bristow (boost_at_[hidden])
Date: 2003-01-24 09:42:32

There is a description of this in the math constants updated docs

http://groups.yahoo.com/group/boost/files/MathConstants/Math_Constants_doc_3.zip

and within the code zip

http://groups.yahoo.com/group/boost/files/MathConstants/Math_constants3.zip

there are function_constants.hpp and a testfunction_constants.cpp file

I have simply used these to provide the code I posted.  And I am still offering
this code (devised by Michael Kenniston) as a possible way of presenting math
constants.  (Ultimately of course, it is the value int MACRO file that is the
real source - even if not used directly, I propose to generate both files form
the same program using NTL).

Your views are most welcome because I feel that it is practical usefulness that
is the major factor in presenting these definitively accurate values.

It looks OK to me (but it needs to compile on the major platforms - I only have
MSVC 7 available, and now discount MSVC 6 because of the need for a dummy type
argument which is unacceptbaly messy for this purpose).

Paul

Paul A Bristow, Prizet Farmhouse, Kendal, Cumbria, LA8 8AB  UK
[phone]   Mobile [phone]
Mobile mailto:pabristow_at_[hidden]
mailto:pbristow_at_[hidden]

> -----Original Message-----
> From: boost-bounces_at_[hidden]
> [mailto:boost-bounces_at_[hidden]]On Behalf Of Joerg Walter
> Sent: Friday, January 24, 2003 12:27 AM
> To: Boost mailing list
> Subject: Re: [boost] RE: math constant - generic function circle_area
> example.
>
>
> Hi Paul,
>
> you wrote:
>
> > > I've been looking into an earlier version of the proposed math constants
> > > before and asked myself how to implement a generic function like
> > >
> > > template<class T>
> > > T circle_area (const T &radius) {
> > >     return math_constants<T>::pi * radius * radius;
> > > }
> > >
> > > How should this be done?
> > >
> > > Thanks,
> > >
> > > Joerg
> >
> > Attached is an example using Michael Kenniston's Kunning Function
> constants.
> >
> > Briefly
> >
> > template <typename T>
> > T circle_area(const T& radius)
> > {
> >   // Usage example: circle_area<double>( 2.) // Explicit type double.
> >   // or             circle_area(2.F) // Implicit type float.
> > return boost::math::constant< T, boost::math::pi_tag >() * radius *
> radius;
> > }
>
> OK. I've tried to compile this with GCC 3.2.1 and after applying some
> remedies like
>
> <for example>
> #ifdef LATER
>   // Define constant is namespaces to hold three builtin floating-point
> representations.
>   namespace float_constants
>   {
>    constant< float, pi_tag > const pi;
>   }
>   namespace double_constants
>   {
>    constant< double, pi_tag > const pi;
>   }
>   namespace long_double_constants
>   {
>    constant< long double, pi_tag > const pi;
>   }
> #endif
> </for example>
>
> it compiled and executed giving the expected results. How is this solution
> related to your latest (Dec. 12) upload at groups.yahoo.com/group/boost?
>
> > It compiles with MSVC 7.0 (but not 6 - see MK's original example for why
> not).
> > (long double == double for MSVC, so long double not fully
> testable/useful).
> >
> > It seems to do the trick, without too many surprises.  I have displayed
> the
> > output using the 17 significant digits for double so one can see the
> difference
> > between a float pi 3.1415927410125732 and a double pi 3.1415926535897931
> (even
> > though only 9 are really significant for float).
> >
> > cout << "circle_area<float>(1.) = "  << circle_area<float>(1.) << endl; //
> > Explicit type float.
> > cout << "circle_area<double>(1.) = "  << circle_area<double>(1.) << endl;
> //
> > Explicit type double.
> > cout << "circle_area(1.F) = "  << circle_area(1.F) << endl; // Implicit
> type
> > float.
> > cout << "circle_area(1.) = "  << circle_area(1.) << endl; // Implicit type
> > double.
> > cout << "circle_area(1.L) = "  << circle_area(1.L) << endl; // implicit
> type
> > long double.
> > cout << "circle_area<double>(1.F) = "  << circle_area<double>(1.F) <<
> endl; //
> > Explicit over-rides implicit.
> >
> > And silly types like int fail helpfully.
> >   // cout << "circle_area(1) = "  << circle_area(1)<< endl; // Implicit
> int -
> > does not link!
> >   // cout << "circle_area<int>(1.) = "  << circle_area<int>(1.)<< endl; //
> > Explicit int - does not compile!
> >
> > Output is
> >
> > Test test_circle_area.cpp Thu Jan 23 00:06:28 2003
> > float pi  = 3.14159274
> > double pi = 3.1415926535897931
> > float pi  = 3.1415927410125732
> > circle_area<float>(1.) = 3.1415927410125732
> > circle_area<double>(1.) = 3.1415926535897931
> > circle_area(1.F) = 3.1415927410125732
> > circle_area(1.) = 3.1415926535897931
> > circle_area(1.L) = 3.1415926535897931
> > circle_area<double>(1.F) = 3.1415926535897931
> > circle_area<long double>(1.) = 3.1415926535897931
> > circle_area<float>(2.) = 12.566370964050293
> > circle_area<double>(2.) = 12.566370614359172
> > circle_area(2.F) = 12.566370964050293
> > circle_area(2.) = 12.566370614359172
> > circle_area(2.L) = 12.566370614359172
> > circle_area<double>(2.F) = 12.566370614359172
> > boost::math::constant< float, boost::math::pi_tag >() 3.1415927410125732
> >
> > I haven't looked at any assembler to check on efficiency, but believe/hope
> from
> > previous examples that it will be optimal if inlined.
> >
> > Does this look sensible/useful?
>
> Only if I learn to see the relation to your latest upload (which I'm
> assuming your review request is related to).
>
> Best,
>
> Joerg
>
>
>
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