On 5/28/05, Arkadiy Vertleyb <vertleyb@hotmail.com> wrote:
"Peder Holt" <peder.holt@gmail.com> wrote
On 5/28/05, Arkadiy Vertleyb <vertleyb@hotmail.com> wrote:
"Peder Holt" <peder.holt@gmail.com> wrote
I did some tests on VC8 beta, and it compiles the testcase in half the time compared to the present implementation of typeof_impl. As far as I have been able to test, it also works around the compiler bug for VC8 discussed earlier.
Here is a more detailed sketch of the proposed solution:
namespace boost {namespace type_of{ template<typename T> struct encode_result { typedef typename encode_type<BOOST_TYPEOF_VECTOR(0)<>, T>::type encoded_type; typedef typename mpl::size<encoded_type>::type size; char (&value0)[...]; char (&value1)[...]; char (&value2)[...]; ... char (&value50)[...]; };
template<class T> encode_result<T> typeof_result(const T&); }} #define BOOST_TYPEOF_AT(n, expr) sizeof(boost::type_of::typeof_result(expr).BOOST_PP_CAT(value,n))
Interesting... Let me guess:
char(&value2)[mpl::at<encode<T>::type, mpl::int<(2 < size) ? 2 : 0>
::type::value]; //?
Yep :)
char(&value2)[mpl::at<encoded_type,mpl::int_<(2 < size::value) ? 2 : 0>
::type::value];
Than there is no magic here :-)
None intended :)
You just re-introduced the simple type optimization I removed to workaround the vc8 problem. Cutting performance in half was the result I got. Apparently in this simpler context vc8 is able to handle this.
Yep. I got no significant performance boost on VC7.1 or GCC with the new version.
This workaround is much better than mine because it doesn't degrade vc8 preformance. And it might be better than the original (before workaround) solution in terms of portability -- other compilers might have the same problem vc8 has. One thing -- we might consider a function template instead of preprocessor-generated values...
Not quite sure how that should work.
Althouth I believe this change _should_ be applied, along with the change that allows to remove _TPL, let's not make these changes now, and consider this more carefully after the review.
Agreed. One more thing, I also tried modifying boost::type_of::vector a bit: struct vector_base { char (&value0)[1]; char (&value1)[1]; char (&value2)[1]; ... char (&value50)[1]; }; template<typename T=void> struct vector0 : vector_base { } template<typename P0,typename T=void> struct vector1 : vector_base { char (&value0)[T0::value]; } ... template<typename P0,..typename P49,typename T=void> struct vector50 : vector_base { ... }; template<class T> typename encode_type<vector0<>,T>::type typeof_result(const T&); This seems to make a ~20% improvement on the VC compilers at least (haven't tried GCC on this change yet) Regards, Peder
Regards, Arkadiy
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