快排过程中参数会是负数？

void QSort(int l, int r)
{
    int lp = l, rp = r, key = (l + r) >> 1;
    while (lp < rp) {
        while (a[lp] < key) lp++;
        while (a[rp] > key) rp--;
        if (lp <= rp)
            swap(&a[lp++], &a[rp--]);
    }
    if (l < rp) QSort(l, rp);
    if (lp < r) QSort(lp, r);
}