1SIMD predefs depend on compiler options. For example, you will have to add the 2option `-msse3` to clang or gcc to enable SSE3. SIMD predefs are also inclusive. 3This means that if SSE3 is enabled, then every other extensions with a lower 4version number will implicitly be enabled and detected. However, some extensions 5are CPU specific, they may not be detected nor enabled when an upper version is 6enabled. 7 8[note SSE(1) and SSE2 are automatically enabled by default when using x86-64 9architecture.] 10 11To check if any SIMD extension has been enabled, you can use: 12 13`` 14#include <boost/predef/hardware/simd.h> 15#include <iostream> 16 17int main() 18{ 19#if defined(BOOST_HW_SIMD_AVAILABLE) 20 std::cout << "SIMD detected!" << std::endl; 21#endif 22 return 0; 23} 24`` 25 26When writing SIMD specific code, you may want to check if a particular extension 27has been detected. To do so you have to use the right architecture predef and 28compare it. Those predef are of the form `BOOST_HW_SIMD_"ARCH"` (where `"ARCH"` 29is either `ARM`, `PPC`, or `X86`). For example, if you compile code for x86 30architecture, you will have to use `BOOST_HW_SIMD_X86`. Its value will be the 31version number of the most recent SIMD extension detected for the architecture. 32 33To check if an extension has been enabled: 34 35`` 36#include <boost/predef/hardware/simd.h> 37#include <iostream> 38 39int main() 40{ 41#if BOOST_HW_SIMD_X86 >= BOOST_HW_SIMD_X86_SSE3_VERSION 42 std::cout << "This is SSE3!" << std::endl; 43#endif 44 return 0; 45} 46`` 47 48[note The *_VERSION* defines that map version number to actual real 49identifiers. This way it is easier to write comparisons without messing up with 50version numbers.] 51 52To *"stricly"* check the most recent detected extension: 53 54`` 55#include <boost/predef/hardware/simd.h> 56#include <iostream> 57 58int main() 59{ 60#if BOOST_HW_SIMD_X86 == BOOST_HW_SIMD_X86_SSE3_VERSION 61 std::cout << "This is SSE3 and this is the most recent enabled extension!" 62 << std::endl; 63#endif 64 return 0; 65} 66`` 67 68Because of the version systems of predefs and of the inclusive property of SIMD 69extensions macros, you can easily check for ranges of supported extensions: 70 71`` 72#include <boost/predef/hardware/simd.h> 73#include <iostream> 74 75int main() 76{ 77#if BOOST_HW_SIMD_X86 >= BOOST_HW_SIMD_X86_SSE2_VERSION &&\ 78 BOOST_HW_SIMD_X86 <= BOOST_HW_SIMD_X86_SSSE3_VERSION 79 std::cout << "This is SSE2, SSE3 and SSSE3!" << std::endl; 80#endif 81 return 0; 82} 83`` 84 85[note Unlike gcc and clang, Visual Studio does not allow you to specify precisely 86the SSE variants you want to use, the only detections that will take place are 87SSE, SSE2, AVX and AVX2. For more informations, 88 see [@https://msdn.microsoft.com/en-us/library/b0084kay.aspx here].] 89 90