pub(crate) const SIZE: usize = 4 /*signature*/ + 4 /*version*/ + 4 /* num entries */; use crate::{util::from_be_u32, Version}; mod error {    use quick_error::quick_error;     quick_error! {        #[derive(Debug)]        pub enum Error {            Corrupt(message: &'static str) {                display("{}", message)            }            UnsupportedVersion(version: u32) {                display("Index version {} is not supported", version)            }        }    }} pub use error::Error; pub(crate) fn decode(data: &[u8], object_hash: git_hash::Kind) -> Result<(crate::Version, u32, &[u8]), Error> {    if data.len() < (3 * 4) + object_hash.len_in_bytes() {        return Err(Error::Corrupt(            "File is too small even for header with zero entries and smallest hash",        ));    }     const SIGNATURE: &[u8] = b"DIRC";    let (signature, data) = data.split_at(4);    if signature != SIGNATURE {        return Err(Error::Corrupt(            "Signature mismatch - this doesn't claim to be a header file",        ));    }     let (version, data) = data.split_at(4);    let version = match from_be_u32(version) {        2 => Version::V2,        3 => Version::V3,        4 => Version::V4,        unknown => return Err(Error::UnsupportedVersion(unknown)),    };    let (entries, data) = data.split_at(4);    let entries = from_be_u32(entries);     Ok((version, entries, data))}