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- SIMD predefs depend on compiler options. For example, you will have to add the
- option `-msse3` to clang or gcc to enable SSE3. SIMD predefs are also inclusive.
- This means that if SSE3 is enabled, then every other extensions with a lower
- version number will implicitly be enabled and detected. However, some extensions
- are CPU specific, they may not be detected nor enabled when an upper version is
- enabled.
- [note SSE(1) and SSE2 are automatically enabled by default when using x86-64
- architecture.]
- To check if any SIMD extension has been enabled, you can use:
- ``
- #include <boost/predef/hardware/simd.h>
- #include <iostream>
- int main()
- {
- #if defined(BOOST_HW_SIMD_AVAILABLE)
- std::cout << "SIMD detected!" << std::endl;
- #endif
- return 0;
- }
- ``
- When writing SIMD specific code, you may want to check if a particular extension
- has been detected. To do so you have to use the right architecture predef and
- compare it. Those predef are of the form `BOOST_HW_SIMD_"ARCH"` (where `"ARCH"`
- is either `ARM`, `PPC`, or `X86`). For example, if you compile code for x86
- architecture, you will have to use `BOOST_HW_SIMD_X86`. Its value will be the
- version number of the most recent SIMD extension detected for the architecture.
- To check if an extension has been enabled:
- ``
- #include <boost/predef/hardware/simd.h>
- #include <iostream>
- int main()
- {
- #if BOOST_HW_SIMD_X86 >= BOOST_HW_SIMD_X86_SSE3_VERSION
- std::cout << "This is SSE3!" << std::endl;
- #endif
- return 0;
- }
- ``
- [note The *_VERSION* defines that map version number to actual real
- identifiers. This way it is easier to write comparisons without messing up with
- version numbers.]
- To *"stricly"* check the most recent detected extension:
- ``
- #include <boost/predef/hardware/simd.h>
- #include <iostream>
- int main()
- {
- #if BOOST_HW_SIMD_X86 == BOOST_HW_SIMD_X86_SSE3_VERSION
- std::cout << "This is SSE3 and this is the most recent enabled extension!"
- << std::endl;
- #endif
- return 0;
- }
- ``
- Because of the version systems of predefs and of the inclusive property of SIMD
- extensions macros, you can easily check for ranges of supported extensions:
- ``
- #include <boost/predef/hardware/simd.h>
- #include <iostream>
- int main()
- {
- #if BOOST_HW_SIMD_X86 >= BOOST_HW_SIMD_X86_SSE2_VERSION &&\
- BOOST_HW_SIMD_X86 <= BOOST_HW_SIMD_X86_SSSE3_VERSION
- std::cout << "This is SSE2, SSE3 and SSSE3!" << std::endl;
- #endif
- return 0;
- }
- ``
- [note Unlike gcc and clang, Visual Studio does not allow you to specify precisely
- the SSE variants you want to use, the only detections that will take place are
- SSE, SSE2, AVX and AVX2. For more informations,
- see [@https://msdn.microsoft.com/en-us/library/b0084kay.aspx here].]
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