Thoughts on Quaternions 1

From: Daryle Walker (darylew_at_[hidden])
Date: 2001-05-20 09:29:07

This class template is from the Special Function library under review.

This is what I did to make the quaternion test run:

1.  My compiler, CodeWarrior Pro 5.3/Mac, must have a problem with
namespaces and explicit template instantiation.  Your code in
"quaternion_test.cpp":

template    class ::boost::quaternion<int>;

wouldn't be accepted.  It gave errors at the first "::", then at the "boost"
when I removed the "::".  I worked around the problem by doing:

// explicit (if ludicrous) instanciation
using boost::quaternion;
template class quaternion<int>;

The template's name must be completely unqualified.  I have something of
this form in my CRC test file, but didn't notice the error because my test
template was already local to the file.  By the way, I don't think MS VC++
can take any kind of explicit template instantiation.

2.  In my comments about sinc_pi and sinhc_pi, I said I commented out the
second versions of those function templates because my compiler couldn't
accept them.  I have to make up that difference here by making custom
versions in "quaternion.hpp":

//=========================================================================
namespace boost
{
    //...

    // Specializations of the index-pi cardinal sine and hyperbolic sine
    template<typename T>
    inline quaternion<T>    sinc_pi(const quaternion<T> x)
    {
        using    ::std::abs;
        using    ::std::sin;
        
        using    ::std::numeric_limits;
        
        if    (abs(x) <= numeric_limits<T>::epsilon())
        {
            return(static_cast< quaternion<T> >(1));
        }
        else
        {
            return(sin(x)/x);
        }
    }

    template<typename T>
    inline quaternion<T>    sinhc_pi(const quaternion<T> x)
    {
        using    ::std::abs;
        using    ::std::sinh;
        
        using    ::std::numeric_limits;
        
        if    (abs(x) <= numeric_limits<T>::epsilon())
        {
            return(static_cast< quaternion<T> >(1));
        }
        else
        {
            return(sinh(x)/x);
        }
    }

}  // boost
//=========================================================================

3.  The I/O functions had a bunch of errors.  The problem was your headers.
The <iosfwd> header is OK if you only need the name of an item, like for a
pointer or a declaration.  If you need an item for a definition, like the
implementation of your I/O operators, you need the item's full declaration.
I commented out the <iosfwd> #include and added #includes for <istream>,
<ostream>, and <sstream> in "quaternion.hpp".

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com