Please send me your amended code.  I had thought that the Kenniston stuff was
included in the zip uploaded, but I will check. Apologies if not.

Thanks

Paul
>  -----Original Message-----
>  From: boost-bounces@[...].org
>  [mailto:boost-bounces@[...].org]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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