[Boost-users] A MPL loop..

Subject: [Boost-users] A MPL loop..
From: Frank Winter (frank.winter_at_[hidden])
Date: 2010-07-11 03:18:27

I am trying to translate this runtime loop

while( totalsize * maxelem * 3 > poolsize )
   maxelem >>= 1;

into MPL. I got so far:

template< typename totalsize , typename maxelement , typename poolsize >
struct loop
{
   typedef mpl::times< totalsize , maxelement > part0;
   typedef mpl::times< part0 , mpl::int_< 3 > > part1;
   typedef mpl::greater< part1 , poolsize > gr;
   typedef mpl::if_< gr , typename loop< totalsize , mpl::divides< maxelement , 
mpl::int_< 2 > > , poolsize >::value , maxelement > value;
};

template< class totalsize , class poolsize >
struct loop< totalsize , mpl::int_< 1 > , poolsize >
{
   typedef mpl::int_< 1 > value;
};

typename loop< mpl::int_< 144 > , mpl::int_< 1024 > , mpl::int_< 140000 > 
> ::value max;

g++43 (GCC) 4.3.2 says:
error: template instantiation depth exceeds maximum of 500

If coded it correctly that should not happen. Since maxelement is already after 
the 1st interation mpl::int_< 512 > and therefor the product with 
mpl::int_< 144 > smaller than mpl::int_< 140000 >

I could imagine:
  - that I need a constructor that converts the divided types, correct?
  - that I need to use a vector< sequence > like in the physics dimension
    example, correct?

Can somebody fix this or point me to a working loop example?

Regards,
Frank