如何快速分别左闭右开和左开右闭？

while (l < r){
    mid = (l + r) >> 1;
    if (check(mid)) r = mid-1;
    else l = mid;
}

while (l < r){
    mid = (l + r + 1) >> 1;
    if (check(mid)) r = mid;
    else l = mid+1;
}

上面这两个分别是什么意思？