// as generated by [PutVarint], to buf and returns the extended buffer.
func AppendVarint(buf []byte, x int64) []byte {
	ux := uint64(x) << 1
	if x < 0 {
		ux = ^ux
	}
	return AppendUvarint(buf, ux)
}

// PutVarint encodes an int64 into buf and returns the number of bytes written.
// If the buffer is too small, PutVarint will panic.
func PutVarint(buf []byte, x int64) int {
	ux := uint64(x) << 1

		ix.sa.int64 = make([]int64, len(data))
		text_64(data, ix.sa.int64)
	}
	return ix
}

// writeInt writes an int x to w using buf to buffer the write.
func writeInt(w io.Writer, buf []byte, x int) error {
	binary.PutVarint(buf, int64(x))
	_, err := w.Write(buf[0:binary.MaxVarintLen64])
	return err
}

// readInt reads an int x from r using buf to buffer the read and returns x.
func readInt(r io.Reader, buf []byte) (int64, error) {

	testConstant(t, 16, MaxVarintLen16)
	testConstant(t, 32, MaxVarintLen32)
	testConstant(t, 64, MaxVarintLen64)
}

func testVarint(t *testing.T, x int64) {
	buf := make([]byte, MaxVarintLen64)
	n := PutVarint(buf, x)
	y, m := Varint(buf[0:n])
	if x != y {
		t.Errorf("Varint(%d): got %d", x, y)
	}
	if n != m {
		t.Errorf("Varint(%d): got n = %d; want %d", x, m, n)
	}

	buf2 := []byte("prefix")