# stdalign

***

**1. Byte-packing structures**

```c
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**

```c
#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**

```c
_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**

```c
#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**

```c
_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**

```c
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**

```c
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**

```c
_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**

```c
_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**

```c
_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**

```c
#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**

```c
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**

```c
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**

```c
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**

```c
#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**

```c
_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**

```c
#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**

```c
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**

```c
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**

```c
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**

```c
_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**

```c
_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**

```c
_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**

```c
_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**

```c
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**

```c
_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**

```c
_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**

```c
_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**

```c
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**

```c
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**

```c
_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**

```c
_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**

```c
_Alignas(256) char *buffer[100

```