Function first_multiple

Eigen/src/Core/util/Memory.h:476–479

  */ 
template<typename Index> 
inline Index first_multiple(Index size, Index base)
{
  return ((size+base-1)/base)*base;
}

// std::copy is much slower than memcpy, so let's introduce a smart_copy which
// use memcpy on trivial types, i.e., on types that does not require an initialization ctor.