Re: [boost] Compile-time power of a run-time base

From: John Maddock (john_at_[hidden])
Date: 2008-02-11 04:30:14

Bruno Lalande wrote:
>> Hi,
>>
>> You will find attached to this mail the header file of the pow
>> function, a cpp test file and the documentation in .qbk format.
>> I tried to write docs and tests in accordance to those found in the
>> math library.
>> The files are ready for integration since I placed them respectively
>> into boost/math, libs/math/test and libs/math/doc in my own
>> environment. Let me know if anything has to be changed or added.
>>
>> I passed the tests on :
>> - gcc-2.95 (debian)
>> - gcc-3.3 (debian)
>> - gcc-3.4 (debian)
>> - gcc-4.1 (kubuntu)
>> - icc-10.1 (debian)
>> - msvc-8.0 (XP SP2)
>> - msvc-9.0 (XP SP2)
>>
>> It didn't compile with msvc-6.5. It's not surprising since, if I
>> remember well, this compiler doesn't handle partial template
>> specialization even with SP5. Is this compiler still officially
>> supported by Boost?
>>
>> There is one case for which I don't know what to do : the
>> pow<negative value>(0) case, which obviously crashes since it
>> consists of computing 1/0. Should I check it and throw something, or
>> let the platform's division by 0 behavior (if any) do its effect? I
>> personally think the first approach is better since it ensures an
>> uniform behavior accross platforms.

Can you follow the error handling policies for overflow here: 
http://svn.boost.org/svn/boost/trunk/libs/math/doc/sf_and_dist/html/math_toolkit/main_overview/error_handling.html ?

You will need to overload pow like this:

template <int N, class T, class Policy>
typename tools::promote_args<T>::type pow(T, const Policy&)
{
  // Actual implementation goes here: uses the specified policy to handle 
errors.
}

template <int N, class T>
inline typename tools::promote_args<T>::type pow(T x)
{
   return pow<N>(x, policies::policy<>());
}

>> The return type is a double. Now I'm going to study the possibility
>> of
>> having different possible return types.

Using boost::math::tools::promote_args<T>::type to calculate the result type 
based on the argument type will work for integer and floating point args: 
not sure how this integrates with Boost.Units though.

Keep up the good work!  John.