[Boost-users] Meta Template Programming with MPL - Compiler Bug or is the code really so evil slow?

13 Feb 2006

      Hi,

I've written a little Meta Template Program which should calculate the 
first 3 perfect numbers. ( range 1 - 500 )

The code is compilable if you use the range 1 - 30 really fast and works 
correctly. But I've tried to compile the code but I can't get it finished.

Someone tried it on a Machine with 40 GB RAM and it now compiles for 
more than 12 hours and uses more than 7.1 GB RAM ( the compilation )

I've tried it by myself with g++ 3.4.x and g++ 4.0.x and with VC++ 7.1

The code works on all tested compilers if the range would be 1 - 30 but

If the range is 1 - 500 VC++ says:

d:\boost\vc71\include\boost-1_33_1\boost\mpl\aux_\preprocessed\plain\apply_wrap.hpp(48): 
fatal error C1204: compiler limit: internal structure overflow.

( This seems to be a known bug in VC++ 
http://support.microsoft.com/default.aspx?scid=kb;en-us;883655 )

and g++ compiles and compiles and uses more and more RAM.

Is the code really so evil slow or is it a compiler Bug in g++?

Maybe anyone has an answer.

BR
evilissimo

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include <iostream>

namespace mpl = boost::mpl;

template < typename Sum , typename Div , typename Num >
struct perf_num_plus_if :
    mpl::if_<
        mpl::equal_to<
            mpl::modulus< Num,Div > ,
            mpl::long_<0>
        >,        
        typename mpl::plus::type,
        Sum
    >::type                
    {};

template< typename Num >
    struct perf_num_impl :
        mpl::accumulate<
            mpl::range_c<
                long,
                1,
                Num::value/2+1
            >,
            mpl::long_<0>,
            perf_num_plus_if<
                mpl::_,
                mpl::_,
                Num
            >
        >::type
    {};

template< long Start , long End >
    struct  perfect_number :
        mpl::copy_if<
            mpl::range_c,
            mpl::equal_to< mpl::_1 , perf_num_implmpl::_1 >,
            mpl::back_inserter< mpl::vector_c<long> >
        >::type
    {};

template< typename Seq , size_t Pos , size_t Max >
    struct Output
    {
        Output()
        {
           std::cout << mpl::at_c::type::value << std::endl;              
           Output< Seq , Pos+1 , Max >();
        }
    };
template< typename Seq , size_t N >
    struct Output< Seq , N , N >
    {
        Output(){}
    };

int main()
{
   typedef perfect_number< 1 , 500 > vec;
   Output< vec , 0 , mpl::size< vec >::value >();
}

[Boost-users] Meta Template Programming with MPL - Compiler Bug or is the code really so evil slow?

Vinzenz 'evilissimo' Feenstra