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#ifndef ALIGN_PTR_H_
#define ALIGN_PTR_H_
#include <stddef.h>
#include <stdint.h>
/**
* ALIGN_PTR_DECL(type, name, num, alignsize):
* Declare a pointer called ${name}, which points to an array large enough to
* contain ${num} values of ${type} and is aligned to ${alignsize} bytes. The
* pointer must not be used until ALIGN_PTR_INIT(${name}, ${alignsize}) has
* been called. This macro may also create an additional variable called
* "${name}_buf".
*/
#define ALIGN_PTR_DECL(type, name, num, alignsize) \
uint8_t name##_buf[num * sizeof(type) + (alignsize - 1)]; \
type * name
/**
* ALIGN_PTR_INIT(name, alignsize):
* Initialize the variable called ${name} to point to an array which is
* aligned to ${alignsize} bytes. They must have previously been declared
* with ALIGN_PTR_DECL(${name}, ${alignsize}). This macro assumes that
* casting a pointer to uintptr_t behaves naturally, i.e. yields a byte offset
* relative to aligned memory.
*/
#define ALIGN_PTR_INIT(name, alignsize) \
name = align_ptr(name##_buf, alignsize)
/**
* align_ptr(arr, alignment):
* Return a pointer to the first memory location within ${arr} which is
* aligned to ${alignsize} bytes. (It is expected that this function will
* only be called via the ALIGN_PTR_INIT macro).
*/
static inline void *
align_ptr(uint8_t * arr, size_t alignment)
{
size_t offset;
/*
* This assumes that casting a pointer to uintptr_t behaves naturally,
* i.e. yields a byte offset relative to aligned memory.
*/
offset = (uintptr_t)(&arr[0]) % alignment;
offset = (alignment - offset) % alignment;
/* Return the aligned pointer. */
return ((void *)&arr[offset]);
}
#endif /* !ALIGN_PTR_H_ */
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