Encode integer `v` to file `f`.

    Parameters
    ----------
    v: int
        Integer v >= 0.
    f: file
        Object containing a write method.

    Returns
    -------
    int
        Number of bytes written.

def encode_varint(v, f):
    """Encode integer `v` to file `f`.

    Parameters
    ----------
    v: int
        Integer v >= 0.
    f: file
        Object containing a write method.

    Returns
    -------
    int
        Number of bytes written.
    """
    assert v >= 0
    num_bytes = 0

    while True:
        b = v % 0x80
        v = v // 0x80

        if v > 0:
            b = b | 0x80

        f.write(FIELD_U8.pack(b))

        num_bytes += 1
        if v == 0:
            break

    return num_bytes