Hi All, I got a compilation error while compiling a library under Win64 arch that includes the boost/numeric/interval/msvc_rounding_control.hpp c:\boost_1.48\include\boost/numeric/interval/detail/msvc_rounding_control.hpp(33) : error C4235: nonstandard extension used : '_asm' keyword not supported on this architecture c:\boost_1.48\include\boost/numeric/interval/detail/msvc_rounding_control.hpp(33) : error C2065: 'FLD' : undeclared identifier c:\boost_1.48\include\boost/numeric/interval/detail/msvc_rounding_control.hpp(34) : error C4235: nonstandard extension used : '_asm' keyword not supported on this architecture So I checked the code under boost/numeric/interval/detail/msvc_rounding_control.hpp and it seems that it does a preprocessor check against WIN64 instead of _WIN64 namespace boost { namespace numeric { namespace interval_lib { namespace detail { #if BOOST_MSVC < 1400 || *defined(WIN64)* extern "C" { double rint(double); } #else inline double rint(double x) { _asm FLD [x] ; _asm FRNDINT ; //_asm RET ; } #endif Is there any reason why do not check against _WIN64 instead of WIN64 since the boost does always check against _WIN64? _WIN64 is also already pre-defined as normal MSVC definition when targeting x86_64 archs. [roberto@roberto include]$ grep -R WIN64 * boost/serialization/force_include.hpp:#elif ! defined(_WIN32) && ! defined(_WIN64) boost/detail/win/synchronization.hpp: #if defined(_WIN64) boost/detail/win/basic_types.hpp:# ifdef _WIN64 boost/intrusive/detail/mpl.hpp:#if defined(_MSC_EXTENSIONS) && !defined(__BORLAND__) && !defined(_WIN64) boost/python/converter/builtin_converters.hpp:# if defined(_MSC_VER) && defined(_WIN64) && PY_VERSION_HEX < 0x03000000 boost/xpressive/xpressive_fwd.hpp:# if (defined(_WIN32) || defined(_WIN64) || defined(_WINCE)) \ boost/thread/win32/thread_primitives.hpp:# ifdef _WIN64 boost/regex/config.hpp:# if(defined(_WIN32) || defined(_WIN64) || defined(_WINCE)) \ boost/signals2/detail/lwm_win32_cs.hpp:#if defined(_WIN64) boost/config/compiler/intel.hpp:#if (!(defined(_WIN32) || defined(_WIN64)) && defined(__STDC_HOSTED__) && (__STDC_HOSTED__ && (BOOST_INTEL_CXX_VERSION <= 1200))) || defined(__GXX_EXPERIMENTAL_CPP0X__) boost/config/compiler/intel.hpp:#if defined(_WIN32) || defined(_WIN64) boost/smart_ptr/detail/lwm_win32_cs.hpp:#if defined(_WIN64) *boost/numeric/interval/detail/msvc_rounding_control.hpp:#if BOOST_MSVC < 1400 || defined(WIN64)*