Re: [Boost-users] [Boost.polygon.voronoi] [Boost.multiprecision] higher precision voronoi

I'm attempting to following the http://www.boost.org/doc/libs/1_53_0_beta1/libs/polygon/doc/voronoi_advanced... to compile boost::polygon::voronoi using 64 bit integer input. I'm using the boost::multiprecision library to do so. Using boost version 1.53 and Microsoft Visual Studio 2012.

The error message is: 1>d:\workspace\movingboundary\boost_1_53_0\boost\polygon\detail\voronoi_robust_fpt.hpp(60): error C2665: 'sqrt' : none of the 3 overloads could convert all the argument types 1> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\math.h(588): could be 'long double sqrt(long double)' 1> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\math.h(540): or 'float sqrt(float)' 1> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\math.h(127): or 'double sqrt(double)' 1> while trying to match the argument list '(const boost::multiprecision::detail::expression)' 1> with 1> [ 1> tag=boost::multiprecision::detail::multiplies, 1> Arg1=boost::multiprecision::detail::expression>,boost::multiprecision::number>,void,void>,boost::multiprecision::detail::expression>,boost::multiprecision::number>,void,void>,void,void>,boost::multiprecision::detail::expression>,boost::multi precision::number>,void,void>,boost::multiprecision::detail::expression>,boost::multiprecision::number>,void,void>,void,void>,void,void>, 1> Arg2=boost::multiprecision::detail::expression>,boost::multiprecision::number>,void,void>,boost::multiprecision::detail::expression>,boost::multiprecision::number>,void,void>,void,void>, 1> Arg3=void, 1> Arg4=void

== reference line is template <typename T> T get_sqrt(const T& that) { return (std::sqrt)(that); //<-- line 60 }

It's a conceptual issue: polynomial is calling std::sqrt, but there is no overload of sqrt for multiprecision types in that namespace: to place them there would actually be mal-formed according to the std. Had polygon been coded like this: template <typename T> T get_sqrt(const T& that) { using std::sqrt; return (sqrt)(that); // ADL is now active } Then the correct overload would have been found. One possible workaround would be to provide an overload of get_sqrt but that would be hard to do in the presence of expression templates :-( Turning them off in the number type you're using would make life much easier, or else I can help with providing expression-template aware overloads. I'd be interested to hear from polygon's authors as to why the library was coded that way, and whether there's any reason not to move to ADL-aware code. HTH, John.