//! Hash functions and hash utilities//!//! With the `fast-sha1` feature, the [`Sha1`] hash type will use a more elaborate implementation utilizing hardware support//! in case it is available.//! Otherwise, a minimal yet performant implementation is used instead for a decent trade-off between compile times and run-time performance. #[cfg(not(feature = "fast-sha1"))]mod _impl {    use super::Sha1Digest;     /// A implementation of the Sha1 hash, which can be used once.    #[derive(Default, Clone)]    pub struct Sha1(sha1::Sha1);     impl Sha1 {        /// Digest the given `bytes`.        pub fn update(&mut self, bytes: &[u8]) {            self.0.update(bytes)        }        /// Finalize the hash and produce a digest.        pub fn digest(self) -> Sha1Digest {            self.0.digest().bytes()        }    }} /// A 20 bytes digest produced by a [`Sha1`] hash implementationpub type Sha1Digest = [u8; 20]; #[cfg(feature = "fast-sha1")]mod _impl {    use super::Sha1Digest;    use fastsha1::Digest;     /// A implementation of the Sha1 hash, which can be used once.    #[derive(Default, Clone)]    pub struct Sha1(fastsha1::Sha1);     impl Sha1 {        /// Digest the given `bytes`.        pub fn update(&mut self, bytes: &[u8]) {            self.0.update(bytes)        }        /// Finalize the hash and produce a digest.        pub fn digest(self) -> Sha1Digest {            self.0.finalize().into()        }    }} pub use _impl::Sha1; /// Compute a CRC32 hash from the given `bytes`, returning the CRC32 hash.////// When calling this function for the first time, `previous_value` should be `0`. Otherwise it/// should be the previous return value of this function to provide a hash of multiple sequential/// chunks of `bytes`.pub fn crc32_update(previous_value: u32, bytes: &[u8]) -> u32 {    crc::crc32::update(previous_value, &crc::crc32::IEEE_TABLE, bytes)} /// Compute a CRC32 value of the given input `bytes`.////// In case multiple chunkes of `bytes` are present, one should use [`crc32_update()`] instead.pub use crc::crc32::checksum_ieee as crc32; /// Compute the hash of `kind` for the bytes in the file at `path`, hashing only the first `num_bytes_from_start`/// while initializing and calling `progress`.////// `num_bytes_from_start` is useful to avoid reading trailing hashes, which are never part of the hash itself.////// # Note////// * Only available with the `git-object` feature enabled due to usage of the [`git_hash::Kind`] enum and the///   [`git_hash::owned::Digest`] return value./// * [Interrupts][crate::interrupt] are supported.pub fn bytes_of_file(    path: impl AsRef<std::path::Path>,    num_bytes_from_start: usize,    kind: git_hash::Kind,    progress: &mut impl crate::progress::Progress,) -> std::io::Result<git_hash::owned::Digest> {    let mut hasher = match kind {        git_hash::Kind::Sha1 => crate::hash::Sha1::default(),    };    let start = std::time::Instant::now();    // init progress before the possibility for failure, as convenience in case people want to recover    progress.init(Some(num_bytes_from_start), crate::progress::bytes());     let mut file = std::fs::File::open(path)?;    use std::io::Read;    const BUF_SIZE: usize = u16::MAX as usize;    let mut buf = [0u8; BUF_SIZE];    let mut bytes_left = num_bytes_from_start;     while bytes_left > 0 {        let out = &mut buf[..BUF_SIZE.min(bytes_left)];        file.read_exact(out)?;        bytes_left -= out.len();        progress.inc_by(out.len());        hasher.update(out);        if crate::interrupt::is_triggered() {            return Err(std::io::Error::new(std::io::ErrorKind::Other, "Interrupted"));        }    }     let id = git_hash::owned::Digest::new_sha1(hasher.digest());    progress.show_throughput(start);    Ok(id)}