#include <stdlib.h>
#include <string.h>

typedef int comp_func(void const *left, void const *right);

static int partition(void *base, size_t size, comp_func *compare,
	int low, int high)
{
	#define AT(n) (base + size * (n))

	__attribute__((aligned(4))) char tmp[size], pivot[size];
	memcpy(pivot, AT((low + high) >> 1), size);

	int i = low - 1;
	int j = high + 1;

	while(1) {
		do i++;
		while(compare(AT(i), pivot) < 0);

		do j--;
		while(compare(AT(j), pivot) > 0);

		if(i >= j) return j;

		memcpy(tmp, AT(i), size);
		memcpy(AT(i), AT(j), size);
		memcpy(AT(j), tmp, size);
	}
}

static void sort(void *base, size_t size, comp_func *compare,
	int low, int high)
{
	if(low >= high) return;

	int p = partition(base, size, compare, low, high);
	sort(base, size, compare, low, p);
	sort(base, size, compare, p+1, high);
}

void qsort(void *base, size_t n, size_t size, comp_func *compare)
{
	sort(base, size, compare, 0, n-1);
}