[WTF] Use system endianess information instead of relying CPU information
Created attachment 327313 [details] Patch
My goal is removing bunch of minor CPUs from Platform.h.
Created attachment 327314 [details] Patch
Comment on attachment 327314 [details] Patch Do we want something that’ll work with C++17? http://en.cppreference.com/w/cpp/types/endian
(In reply to JF Bastien from comment #4) > Comment on attachment 327314 [details] > Patch > > Do we want something that’ll work with C++17? > http://en.cppreference.com/w/cpp/types/endian In our current use cases, we need preprocessor defines to switch implementation by ifdefs. But C++ enum would work well if we implement things and switch by it. template<std::endian> void implementation(); template<> void implementation<std::endian::little>() { ...; } template<> void implementation<std::endian::big>() { ...; } And layout change is like, template<std::endian> struct Layout; template<> struct Layout<std::endian::big> { uint8_t f0; uint8_t f1; }; template<> struct Layout<std::endian::little> { uint8_t f1; uint8_t f0; }; I'm not sure how to handle PDP endian (a.k.a. middle endian) in C++17.
(In reply to Yusuke Suzuki from comment #5) > (In reply to JF Bastien from comment #4) > > Comment on attachment 327314 [details] > > Patch > > > > Do we want something that’ll work with C++17? > > http://en.cppreference.com/w/cpp/types/endian > > In our current use cases, we need preprocessor defines to switch > implementation by ifdefs. But C++ enum would work well if we implement > things and switch by it. Sounds like you'd rather do that separately? Sounds fine, I just figured I would ask! :) Shame that the proposal didn't have a feature test macro so we could conditionally use it when available :( > I'm not sure how to handle PDP endian (a.k.a. middle endian) in C++17. Can we just static_assert that we never get such endian? I don't think WebKit supports this type of platform? Otherwise r=me
(In reply to JF Bastien from comment #6) > (In reply to Yusuke Suzuki from comment #5) > > (In reply to JF Bastien from comment #4) > > > Comment on attachment 327314 [details] > > > Patch > > > > > > Do we want something that’ll work with C++17? > > > http://en.cppreference.com/w/cpp/types/endian > > > > In our current use cases, we need preprocessor defines to switch > > implementation by ifdefs. But C++ enum would work well if we implement > > things and switch by it. > > Sounds like you'd rather do that separately? Sounds fine, I just figured I > would ask! :) > > Shame that the proposal didn't have a feature test macro so we could > conditionally use it when available :( Yeah, I think currently using CPU(LITTLE_ENDIAN) / CPU(BIG_ENDIAN) is enough for WebKit. But once C++17 is everywhere, we can consider using std::endian instead in our code base. > > > I'm not sure how to handle PDP endian (a.k.a. middle endian) in C++17. > > Can we just static_assert that we never get such endian? I don't think > WebKit supports this type of platform? > > Otherwise r=me Right, I think the current WebKit does not support middle endian well. And I don't think there are any stake holders using middle endian CPUs. I'll add `static_assert(!CPU(MIDDLE_ENDIAN), "");` to ensure this.
(In reply to Yusuke Suzuki from comment #7) > (In reply to JF Bastien from comment #6) > > (In reply to Yusuke Suzuki from comment #5) > > > (In reply to JF Bastien from comment #4) > > > > Comment on attachment 327314 [details] > > > > Patch > > > > > > > > Do we want something that’ll work with C++17? > > > > http://en.cppreference.com/w/cpp/types/endian > > > > > > In our current use cases, we need preprocessor defines to switch > > > implementation by ifdefs. But C++ enum would work well if we implement > > > things and switch by it. > > > > Sounds like you'd rather do that separately? Sounds fine, I just figured I > > would ask! :) > > > > Shame that the proposal didn't have a feature test macro so we could > > conditionally use it when available :( > > Yeah, I think currently using CPU(LITTLE_ENDIAN) / CPU(BIG_ENDIAN) is enough > for WebKit. But once C++17 is everywhere, we can consider using std::endian > instead in our code base. > > > > > > I'm not sure how to handle PDP endian (a.k.a. middle endian) in C++17. > > > > Can we just static_assert that we never get such endian? I don't think > > WebKit supports this type of platform? > > > > Otherwise r=me > > Right, I think the current WebKit does not support middle endian well. > And I don't think there are any stake holders using middle endian CPUs. > I'll add `static_assert(!CPU(MIDDLE_ENDIAN), "");` to ensure this. Since it's macro, and we do not want to add any C++ things to Platform.h, I'll insert #if !CPU(LITTLE_ENDIAN) && !CPU(BIG_ENDIAN) #error Unsupported endian #endif
Committed r225032: <https://trac.webkit.org/changeset/225032>
<rdar://problem/35635902>