内存分配中的对齐操作

#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;

}

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