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1.. title:: clang-tidy - altera-struct-pack-align2 3altera-struct-pack-align4========================5 6Finds structs that are inefficiently packed or aligned, and recommends7packing and/or aligning of said structs as needed.8 9Structs that are not packed take up more space than they should, and accessing10structs that are not well aligned is inefficient.11 12Fix-its are provided to fix both of these issues by inserting and/or amending13relevant struct attributes.14 15Based on the `Altera SDK for OpenCL: Best Practices Guide16<https://www.altera.com/en_US/pdfs/literature/hb/opencl-sdk/aocl_optimization_guide.pdf>`_.17 18.. code-block:: c++19 20 // The following struct is originally aligned to 4 bytes, and thus takes up21 // 12 bytes of memory instead of 10. Packing the struct will make it use22 // only 10 bytes of memory, and aligning it to 16 bytes will make it23 // efficient to access.24 struct example {25 char a; // 1 byte26 double b; // 8 bytes27 char c; // 1 byte28 };29 30 // The following struct is arranged in such a way that packing is not needed.31 // However, it is aligned to 4 bytes instead of 8, and thus needs to be32 // explicitly aligned.33 struct implicitly_packed_example {34 char a; // 1 byte35 char b; // 1 byte36 char c; // 1 byte37 char d; // 1 byte38 int e; // 4 bytes39 };40 41 // The following struct is explicitly aligned and packed.42 struct good_example {43 char a; // 1 byte44 double b; // 8 bytes45 char c; // 1 byte46 } __attribute__((packed)) __attribute__((aligned(16));47 48 // Explicitly aligning a struct to the wrong value will result in a warning.49 // The following example should be aligned to 16 bytes, not 32.50 struct badly_aligned_example {51 char a; // 1 byte52 double b; // 8 bytes53 char c; // 1 byte54 } __attribute__((packed)) __attribute__((aligned(32)));55