public static byte[] swapLongs(byte b[], int off, int len) {
        checkLength(len, 8);
        for (int i = off, n = off + len; i < n; i += 8) {
            swap(b, i, i+7);
            swap(b, i+1, i+6);
            swap(b, i+2, i+5);
            swap(b, i+3, i+4);
        }
        return b;
    }
@Test
    public void testSwapLongs() {
        assertArrayEquals(DOUBLE_PI_LE ,
                ByteUtils.swapLongs(DOUBLE_PI_BE.clone(), 0,
                        DOUBLE_PI_BE.length));
    }