C-merge-sort

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int a[200000] = {0};
#define SIZE sizeof(a)/sizeof(int)
int* merge_sort(int* a,int length)
{
    int* buff = (int*)malloc(sizeof(int)*length);
    int* array = (int*)malloc(sizeof(int)*length);
    memcpy(array,a,length*sizeof(int));
    int i;
    if(length == 1)
    {
        free(buff);
        return array;
    }
    int* tmp;
    int size = 1;
    while(size < length)
    {
        int s;
        int i;
        int j;
        for(s = 0; s <= length/size+1; s += size*2)
        {
            i = s;
            j = s + size;
            int o = s;
            while(!((i >= s + size) &&
                        ((j >= s + size*2) || j >= length)
                   ))
            {
                if(j >= s + size*2 || j >= length)
                    buff[o++] = array[i++];
                else if (i >= s + size)
                    buff[o++] = array[j++];
                else if (array[i] > array[j])
                    buff[o++] = array[j++];
                else
                    buff[o++] = array[i++];
            }
        }
        tmp = buff;
        buff = array;
        array = tmp;
        size *= 2;
    }
    free(buff);
    return array;
}
int main()
{
    int i;
    //  for(i= 0; i < SIZE; i ++)
    //      printf("%d ",a[i]);
    //  printf("\n");
    int* sorted = merge_sort(a,SIZE);
    //  for(i= 0; i < SIZE; i ++)
    //      printf("%d ",sorted[i]);
    //  printf("\n");
    free(sorted);
}