use crate::data;use gix_error::ErrorExt; pub(crate) const N32_SIZE: usize = std::mem::size_of::<u32>(); /// The number of bytes in a pack file header.pub const SIZE: usize = b"PACK".len() + N32_SIZE * 2; /// Parses the first 12 bytes of a pack file, returning the pack version as well as the number of objects contained in the pack.pub fn decode(data: &[u8; SIZE]) -> Result<(data::Version, u32), gix_error::Exn> {    let mut ofs = 0;    if &data[ofs..ofs + b"PACK".len()] != b"PACK" {        return Err(gix_error::CorruptionError::new("Pack data type not recognized").raise_erased());    }    ofs += N32_SIZE;    let kind = match crate::read_u32(&data[ofs..ofs + N32_SIZE]) {        2 => data::Version::V2,        3 => data::Version::V3,        v => return Err(gix_error::ValidationError::new(format!("Unsupported pack version: {v}")).raise_erased()),    };    ofs += N32_SIZE;    let num_objects = crate::read_u32(&data[ofs..ofs + N32_SIZE]);     Ok((kind, num_objects))} /// Write a pack data header at `version` with `num_objects` and return a buffer.pub fn encode(version: data::Version, num_objects: u32) -> [u8; SIZE] {    use crate::data::Version::*;    let mut buf = [0u8; SIZE];    buf[..4].copy_from_slice(b"PACK");    buf[4..8].copy_from_slice(        &match version {            V2 => 2u32,            V3 => 3,        }        .to_be_bytes()[..],    );    buf[8..].copy_from_slice(&num_objects.to_be_bytes()[..]);    buf}