Useful aligned malloc function

[jboldiga]

Here is a useful aligned malloc function you can use for when dynamically allocating vertex data for 3D stuff. Enjoy.

Example use:

Code: Select all

typedef struct Vertex
{
	float u, v;
	float x, y, z;
}Vertex;

Vertex* vertices;
int  numVerts = 36;

// 16 byte aligned memory block
vertices = aligned_malloc(numVerts * sizeof(Vertex), 16);

And here is the source:

Code: Select all

// returns a block of memory aligned to "alignSize" bytes
void* aligned_malloc(size_t size, size_t alignSize) 
{
	void**	ptr;
	void**	alignedPtr;

	ptr = (void*)malloc(size + alignSize + sizeof(void*));
	
	if(ptr == NULL) 
		return(NULL);

	alignedPtr			= (void**)((int)(ptr) & 0xfffffff0);
	*alignedPtr++	    = ptr;

	return(alignedPtr);
}

// frees an aligned block of memory
void aligned_free(void* ptr) 
{
	void* ptr2 = *((void**)ptr - 1);
	free(ptr2);
}

[ooPo]

Why not just use memalign()?

[jboldiga]

cuz didnt know there was a memalign in libc :)

[ooPo]

Well, at least you learned something about malloc in the process. :)

[Jim]

Code: Select all

ptr = (void*)malloc(size + alignSize + sizeof(void*)); 
alignedPtr         = (void**)((int)(ptr) & 0xfffffff0);
*alignedPtr++       = ptr;

ooh, nasty bug :-p
Use memalign :-)

Jim