CGAL users discussion list

[Marc Glisse <>]

On Mon, 23 May 2011, Costas Tsirogiannis wrote:

>  int byte_size( NT a)
> { return sizeof(CGAL::Lazy_exact_nt<CGAL::Gmpq>) -
> sizeof(CGAL::Gmpq)+a.exact().size(); }  (That I learned from a previous
> question here, thanks :) )
>
>  But, in fact, the "exact().size()"  function forces the exact part of the
> object to be computed even if algebraic filtering was sufficient to avoid
> this computation so far. Thus, then we get an overestimation of what is
> computed by the algorithm.  It's like a "schrodinger" phenomenon: to read
> the byte-size, you have to force the computation of the exact part.
>
> Is there a way then to detect for a lazy_exact_nt object if the exact part
> is not computed so far?

There is an undocumented (so don't rely on it) but public method 
is_lazy().

> In other words, given a geometric structure whose
> coordinates are represented with this number type,  can one measure the
> number of bytes which are used for the structure's representation, no more,
> no less?

You would need to walk the whole tree for that, which is not easily done. 
If your program has mostly just this structure in memory, your best bet is 
to ask your implementation how much memory it has allocated (see mallinfo 
with glibc).

--
Marc Glisse