Solution
#include <iostream>
using namespace std;
int aligned_malloc(void **memptr, size_t alignment, size_t size)
{
size_t len = size + alignment + sizeof(void *);
void *ptr = malloc(len);
if(ptr == NULL){
return 0;
}
*memptr = (unsigned int *)((((unsigned)ptr) + alignment + sizeof(void *)) & ~(alignment - 1));
*((unsigned int *)(((unsigned int *)*memptr) - 1)) = (unsigned)ptr;
return 1;
}
int aligned_free(void *memptr)
{
if(memptr == NULL){
return 0;
}
else{
free((void *)(*((unsigned int *)memptr - 1)));
return 1;
}
}
int main(int argc, char* argv[])
{
for(int i = 1; i < 257; i *= 2){
void *memptr = NULL;
aligned_malloc(&memptr, i, 1000);
cout << "aligned :" << i << " -- " << hex << (unsigned)memptr << endl;
aligned_free(memptr);
}
return 0;
}
Output
aligned :1 -- 396445
aligned :2 -- 396446
aligned :4 -- 396448
aligned :8 -- 396448
aligned :10 -- 396b20
aligned :20 -- 396b20
aligned :40 -- 396b40
aligned :80 -- 396b80
aligned :100 -- 396c00
Problem
Write an aligned malloc & free function that takes number of bytes and aligned byte (which is always power of 2)