- C++17 and alignment... - 1 Update
- atomic<>-costs - 1 Update
| "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: Jan 21 03:17PM -0800 Thanks to Bonita, I learned that C++17 actually works with alignas wrt using new. This is very nice and am looking forward to using it quite a bit. Here is some crude sample code: can you compile it, and what is your output? Do you get any Crap? ;^) _________________________ #include <iostream> #include <atomic> #include <cstdint> #include <cstdlib> static constexpr std::size_t ct_page_size = 8192; static constexpr std::size_t ct_l2_cacheline_size = 64; struct alignas(ct_l2_cacheline_size) ct_cacheline { std::atomic<std::uint64_t> m_state; }; struct alignas(ct_page_size) ct_page { ct_cacheline m_line_0; ct_cacheline m_line_1; }; int main() { if (sizeof(ct_cacheline) != ct_l2_cacheline_size) { std::cout << "Crap! ct_cacheline is not padded!\n"; } if (sizeof(ct_page) != ct_page_size) { std::cout << "Crap! ct_page is not padded!\n"; } ct_page* page = new ct_page; std::cout << "page = " << page << "\n"; if ((std::uintptr_t)(page) % ct_page_size) { std::cout << "Crap! page is not aligned!\n"; } if ((std::uintptr_t)(&page->m_line_1) % ct_l2_cacheline_size) { std::cout << "Crap! page->m_line_1 is not aligned!\n"; } delete page; return 0; } _________________________ Now it seems as if alignas, at least on MSVC has a "limit". For instance I am getting a compile time error using a ct_page_size of 8192 * 4. _________________________ Error C2345 align(32768): illegal alignment value Well, I am wondering why this would be a limitation? _________________________ Thanks. |
| "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: Jan 21 02:25PM -0800 On 1/21/2021 2:23 PM, Chris M. Thomasson wrote: > I installed MSVC 2019, and your code still does not work. I am getting: > doesn't fit > What am I doing wrong here? DOH! I was not compiling in C++17 mode. So, now it works. Cool. Thanks. |
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