#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum EbmlSize {
    Exact(usize),
    Unknown,
}
impl EbmlSize {
    pub fn from_vint((value, len): (u64, usize)) -> EbmlSize {
        if value == ((1 << (7 * len)) - 1) {
            Self::Unknown
        } else {
            Self::Exact(value as usize)
        }
    }
    pub fn some(self) -> Option<usize> {
        match self {
            EbmlSize::Exact(s) => Some(s),
            EbmlSize::Unknown => None,
        }
    }
}