#include <iostream>

#include <assert.h>

using namespace std;

/*

* http://stackoverflow.com/questions/227897/solve-the-memory-alignment-in-c-interview-question-that-stumped-me

* Q: How would you allocate 1024 bytes of memory, and align it to a 16 byte boundary?

* and free after allocate

* http://jongampark.wordpress.com/2008/06/12/implementation-of-aligned-memory-alloc/

*/

void * memset_16aligned() {

/* allocate a buffer with room to add 0-15 bytes to ensure 16-alignment*/

void *mem = malloc(1024+15);

assert(mem); // some kind of error handling

/* round up to multiple of 16, add 15 and round down by masking*/

void *ptr = (void *)(((unsigned long)mem + 15) & ~0x0f);

// free memory

free(mem);

}

/*

* For more generic memeory allocation function, without tracking two pointer

* one to use (ptr) and one to free (mem)

* idea is to store a pointer which points to real buffer below the aligned buffer

*/

void * aligned_malloc(size_t size, int align) {

// alignment could not be less than 0

if (size<0) {

return NULL;

}

// allocate necessary memory for

// requested size +

// alignment +

// area to store the address of memory returned by malloc

void *p = malloc(size + align-1 + sizeof(void *));

if (p == NULL) {

return NULL;

}

// address of the aligned memory according to the align parameter

void *ptr = (void *) (((unsigned long)p + sizeof(void *) + align-1) & ~(align-1));

// store th address of mallc() above at the beginning of our total memory area

*((void **)ptr -1) = p;

// return the address of aligned memory

return ptr;

}

void aligned_free(void *p) {

// Get address of the memory from start of total memory area

free ( *( (void **)p - 1) );

}

int main() {

void * ptr = aligned_malloc(10, 4);

printf("aligned address %ld \n", (unsigned long)ptr);

aligned_free(ptr);

return 1;

}