stdalign

1. Byte-packing structures

struct PackedStruct {
  _Alignas(1) char byte1;
  _Alignas(2) short byte2;
  _Alignas(4) int byte3;
};

This ensures that byte1 is aligned on a 1-byte boundary, byte2 on a 2-byte boundary, and byte3 on a 4-byte boundary, optimizing memory access performance.

2. Hardware alignment requirements

#define SIMD_ALIGNMENT 16

struct SIMDVector {
  _Alignas(SIMD_ALIGNMENT) float vec[4];
};

This ensures that when accessing the vec array, the SIMD instructions are executed efficiently, without causing cache misses or performance penalties.

3. Alignment for performance-critical code

_Alignas(64) char *ptr = malloc(1024);

Aligning memory allocations on a 64-byte boundary can improve performance for memory-intensive operations, such as vector computations or high-speed data transfers.

4. Cross-platform alignment

#if __STDC_VERSION__ >= 201112L
  _Alignas(16) int arr[100];
#else
  int arr[100] __attribute__ ((aligned(16)));
#endif

This ensures that the array arr is aligned on a 16-byte boundary, regardless of the compiler or platform, providing consistent performance.

5. Custom alignment

_Alignas(sizeof(long long double)) long long double value;

This aligns the value variable on a boundary that matches the alignment of the long long double data type, ensuring efficient access.

6. Unaligned memory access mitigation

char *unaligned_ptr;
_Alignas(16) char aligned_buffer[16];

memcpy(aligned_buffer, unaligned_ptr, 16);

This example copies data from an unaligned memory location to an aligned buffer, allowing efficient access to the data later.

7. Cache-friendly data structures

struct CacheLineAlignedStruct {
  _Alignas(64) int data[16];
};

This aligns the data array on a 64-byte boundary, optimizing cache performance by ensuring that the entire array fits within a single cache line.

8. Vector data alignment

_Alignas(64) float vec[16];

Aligning the vector vec on a 64-byte boundary allows efficient vector operations, such as SIMD calculations or matrix transformations.

9. Multithreaded data sharing

_Atomic(_Alignas(64)) int shared_var;

Aligning the shared_var atomic variable on a 64-byte boundary ensures consistent cache behavior across multiple threads, reducing synchronization overhead.

10. SIMD vector optimization

_Alignas(16) int vec[4];

_Alignas(16) int *vec_ptr = &vec;
_Alignas(16) int var = *vec_ptr;

This example aligns the vec array and the pointer vec_ptr on a 16-byte boundary, enabling efficient SIMD operations, such as vector loads and stores.

11. Hardware-specific alignment requirements

#ifdef __ARM_ARCH
  _Alignas(8) int arr[10];
#else
  _Alignas(4) int arr[10];
#endif

This ensures that the array arr is aligned on the appropriate boundary, as specified by the ARM or non-ARM hardware architecture.

12. Aligning function arguments

void aligned_func(_Alignas(16) int *arr);

Aligning the function argument arr on a 16-byte boundary optimizes its passing to the function, reducing the overhead of parameter copying.

13. Structure padding removal

struct PaddedStruct {
  int x;
  char *ptr;
};

struct AlignedStruct {
  _Alignas(sizeof(void *)) struct PaddedStruct s;
};

Aligning the s member of AlignedStruct on a boundary that matches the size of the ptr pointer removes unnecessary padding, reducing memory consumption.

14. Memory allocation hints

void *ptr;

posix_memalign(&ptr, 16, 1024);

This allocates memory aligned on a 16-byte boundary, optimizing its use for alignment-sensitive operations.

15. Data parallel operations

#pragma omp parallel for aligned
for (int i = 0; i < 100; i++) {
  _Alignas(16) int arr[100];
}

The aligned clause ensures that the loop iterations are executed on aligned memory, improving performance for data parallel operations.

16. DMA transfers

_Alignas(64) float buf[1024];

Aligning the buf buffer on a 64-byte boundary optimizes Direct Memory Access (DMA) transfers, reducing the overhead of data alignment during data movement.

17. Packed SIMD data

#include <x86intrin.h>

_Alignas(32) __m256i packed_data;

Aligning the packed_data variable on a 32-byte boundary optimizes operations using SSE intrinsics, such as vector additions and multiplications.

18. Memory mapping

void *ptr;

ptr = mmap(NULL, 1024, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ALIGNED_ SUPER, -1, 0);

This maps memory aligned on the system page size, typically 4096 bytes, optimizing performance for memory-intensive operations.

19. Cache-aware data structures

struct CacheAwareStruct {
  _Alignas(64) int *data;
};

Aligning the data pointer on a 64-byte boundary optimizes cache performance by ensuring that the data structure fits within a single cache line.

20. Accelerating computations

void func(_Alignas(64) float *arr) {
  // Perform computations on aligned data
}

Aligning the arr array on a 64-byte boundary improves the efficiency of vectorized and parallelized computations, reducing execution time.

21. Efficient pointer arithmetic

_Alignas(4) int *ptr;

ptr += 4;

Aligning the ptr pointer on a 4-byte boundary ensures that pointer increment and decrement operations align with the underlying data type.

22. Optimized data access

_Alignas(16) int *arr;

int val = arr[0];

Aligning the arr array on a 16-byte boundary optimizes data access by ensuring that individual elements are accessed on the appropriate alignment boundaries.

23. Reducing memory fragmentation

_Alignas(256) int *arr;

Aligning the arr array on a 256-byte boundary reduces memory fragmentation by allocating larger chunks of aligned memory, minimizing the overhead of managing small memory blocks.

24. Improved performance for virtualized environments

_Alignas(4096) char *buf;

Aligning the buf buffer on a 4096-byte boundary improves performance in virtualized environments by matching the page size, reducing the overhead of page table translations.

25. Aligning structures in packed memory regions

struct PackedStruct {
  _Alignas(16) int x;
  _Alignas(16) int y;
};

Aligning the members of PackedStruct on a 16-byte boundary ensures efficient access when the structure is packed into a contiguous memory region.

26. Aligning data for streaming operations

_Alignas(32) float *data;

Aligning the data array on a 32-byte boundary optimizes streaming operations, such as network I/O or multimedia data processing, by matching the alignment of streaming buffers.

27. Multi-threading performance optimization

_Atomic(_Alignas(32)) int shared_value;

Aligning the shared_value atomic variable on a 32-byte boundary improves performance in multi-threaded environments by reducing the overhead of atomic operations.

28. Aligning matrices for efficient operations

_Alignas(64) float matrix[16][16];

Aligning the matrix array on a 64-byte boundary optimizes linear algebra operations, such as matrix multiplication, by reducing the overhead of accessing individual matrix elements.

29. Reducing cache misses for data structures

struct CacheOptimisedStruct {
  _Alignas(64) int *arr;
  _Alignas(64) float *data;
};

Aligning the arr and data members of CacheOptimisedStruct on a 64-byte boundary reduces cache misses when accessing the members together, improving performance.

30. Aligning function pointers

typedef void (*AlignedFuncPtr)(_Alignas(16) int *);

Aligning the function pointer on a 16-byte boundary ensures efficient function calls when passing aligned arguments.

31. Aligning data for efficient vectorization

_Alignas(64) float arr[1024];

Aligning the arr array on a 64-byte boundary enables efficient vectorization of operations on the array, improving performance.

32. Ensuring memory alignment for critical sections

_Alignas(16) volatile int lock;

while (lock > 0);

Aligning the lock variable on a 16-byte boundary ensures efficient access in critical sections, reducing contention and improving synchronization performance.

33. Optimizing memory access for large data structures

_Alignas(256) char *buffer[100

Previoussignal Nextstdarg