pub(crate) const SIZE: usize = 4 /*signature*/ + 4 /*version*/ + 4 /* num entries */; use crate::{util::from_be_u32, Version}; pub(crate) const SIGNATURE: &[u8] = b"DIRC"; mod error {     /// The error produced when failing to decode an index header.    #[derive(Debug, thiserror::Error)]    #[allow(missing_docs)]    pub enum Error {        #[error("{0}")]        Corrupt(&'static str),        #[error("Index version {0} is not supported")]        UnsupportedVersion(u32),    }}pub use error::Error; pub(crate) fn decode(data: &[u8], object_hash: git_hash::Kind) -> Result<(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",        ));    }     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))}