CGAL users discussion list

[Sylvain Pion <>]

Le 20/08/10 11:58, Costas Tsirogiannis a écrit :
> Greetings,
>
> I have built a Polyhedron_3 object using Gmpq as NT.  What I want to do is to 
> compute the exact bit-size of the structure.
>
> This object that I compute contains vertices that were already part of the 
> input plus vertices constructed from line intersections.  So not all the 
> vertex coordinates have the same bit size. The Polyhedron_3 class has a 
> member function bytes() which just gives a standard answer:
>
> sizeof(Vertex_type)*number_of_vertices()+sizeof(Facet_type)*number_of_facets()
>
> But this must not be exact since Gmpq can have an arbitrary number of bits, 
> right? Theoretically, the bit-size of the coordinates of a single vertex in 
> the structure that I compute can be very high (can actually be comparable to 
> the size of the entire input) so this function does not really help me. Any 
> suggestions of how can I compute the exact bit size here or, at least, how 
> can I compute the exact bit-size of a single Gmpq object?

Looking at the Gmpq class, I see :

  // Gives the memory size in bytes. (not documented yet)
  std::size_t size() const
  {
    std::size_t s_num = mpz_size(mpq_numref(mpq())) * (mp_bits_per_limb/8);
    std::size_t s_den = mpz_size(mpq_denref(mpq())) * (mp_bits_per_limb/8);
    return s_num + s_den;
  }

--
Sylvain