use std::cmp::Ordering;use quick_error::quick_error;use crate::{oid, ObjectId, Prefix};quick_error! { /// The error returned by [Prefix::try_from_id()][super::Prefix::try_from_id()]. #[derive(Debug)] #[allow(missing_docs)] pub enum Error { TooShort { hex_len: usize } { display("The minimum hex length of a short object id is 4, got {}", hex_len) } TooLong { object_kind: crate::Kind, hex_len: usize } { display("An object of kind {} cannot be larger than {} in hex, but {} was requested", object_kind, object_kind.len_in_hex(), hex_len) } }}impl Prefix { /// Create a new instance by taking a full `id` as input and truncating it to `hex_len`. /// /// For instance, with `hex_len` of 7 the resulting prefix is 3.5 bytes, or 3 bytes and 4 bits /// wide, with all other bytes and bits set to zero. pub fn new(id: impl AsRef<oid>, hex_len: usize) -> Result<Self, Error> { let id = id.as_ref(); if hex_len > id.kind().len_in_hex() { Err(Error::TooLong { object_kind: id.kind(), hex_len, }) } else if hex_len < 4 { Err(Error::TooShort { hex_len }) } else { let mut prefix = ObjectId::null(id.kind()); let b = prefix.as_mut_slice(); let copy_len = (hex_len + 1) / 2; b[..copy_len].copy_from_slice(&id.as_bytes()[..copy_len]); if hex_len % 2 == 1 { b[hex_len / 2] &= 0xf0; } Ok(Prefix { bytes: prefix, hex_len }) } } /// Returns the prefix as object id. /// /// Note that it may be deceptive to use given that it looks like a full /// object id, even though its post-prefix bytes/bits are set to zero. pub fn as_oid(&self) -> &oid { &self.bytes } /// Return the amount of hexadecimal characters that are set in the prefix. /// /// This gives the prefix a granularity of 4 bits. pub fn hex_len(&self) -> usize { self.hex_len } /// Provided with candidate id which is a full hash, determine how this prefix compares to it, /// only looking at the prefix bytes, ignoring everything behind that. pub fn cmp_oid(&self, candidate: &oid) -> Ordering { let common_len = self.hex_len / 2; self.bytes.as_bytes()[..common_len] .cmp(&candidate.as_bytes()[..common_len]) .then(if self.hex_len % 2 == 1 { let half_byte_idx = self.hex_len / 2; self.bytes.as_bytes()[half_byte_idx].cmp(&(candidate.as_bytes()[half_byte_idx] & 0xf0)) } else { Ordering::Equal }) } /// Create an instance from the given hexadecimal prefix, e.g. `35e77c16` would yield a `Prefix` with `hex_len()` = 8. pub fn from_hex(_hex: &str) -> Self { todo!("Prefix::from_hex()") }}impl std::fmt::Display for Prefix { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { self.bytes.to_hex_with_len(self.hex_len).fmt(f) }}
use std::cmp::Ordering;
use quick_error::quick_error;
use crate::{oid, ObjectId, Prefix};
quick_error! {
/// The error returned by [Prefix::try_from_id()][super::Prefix::try_from_id()].
#[derive(Debug)]
#[allow(missing_docs)]
pub enum Error {
TooShort { hex_len: usize } {
display("The minimum hex length of a short object id is 4, got {}", hex_len)
}
TooLong { object_kind: crate::Kind, hex_len: usize } {
display("An object of kind {} cannot be larger than {} in hex, but {} was requested", object_kind, object_kind.len_in_hex(), hex_len)
}
}
}
impl Prefix {
/// Create a new instance by taking a full `id` as input and truncating it to `hex_len`.
///
/// For instance, with `hex_len` of 7 the resulting prefix is 3.5 bytes, or 3 bytes and 4 bits
/// wide, with all other bytes and bits set to zero.
pub fn new(id: impl AsRef<oid>, hex_len: usize) -> Result<Self, Error> {
let id = id.as_ref();
if hex_len > id.kind().len_in_hex() {
Err(Error::TooLong {
object_kind: id.kind(),
hex_len,
})
} else if hex_len < 4 {
Err(Error::TooShort { hex_len })
} else {
let mut prefix = ObjectId::null(id.kind());
let b = prefix.as_mut_slice();
let copy_len = (hex_len + 1) / 2;
b[..copy_len].copy_from_slice(&id.as_bytes()[..copy_len]);
if hex_len % 2 == 1 {
b[hex_len / 2] &= 0xf0;
}
Ok(Prefix { bytes: prefix, hex_len })
}
}
/// Returns the prefix as object id.
///
/// Note that it may be deceptive to use given that it looks like a full
/// object id, even though its post-prefix bytes/bits are set to zero.
pub fn as_oid(&self) -> &oid {
&self.bytes
}
/// Return the amount of hexadecimal characters that are set in the prefix.
///
/// This gives the prefix a granularity of 4 bits.
pub fn hex_len(&self) -> usize {
self.hex_len
}
/// Provided with candidate id which is a full hash, determine how this prefix compares to it,
/// only looking at the prefix bytes, ignoring everything behind that.
pub fn cmp_oid(&self, candidate: &oid) -> Ordering {
let common_len = self.hex_len / 2;
self.bytes.as_bytes()[..common_len]
.cmp(&candidate.as_bytes()[..common_len])
.then(if self.hex_len % 2 == 1 {
let half_byte_idx = self.hex_len / 2;
self.bytes.as_bytes()[half_byte_idx].cmp(&(candidate.as_bytes()[half_byte_idx] & 0xf0))
} else {
Ordering::Equal
})
}
/// Create an instance from the given hexadecimal prefix, e.g. `35e77c16` would yield a `Prefix` with `hex_len()` = 8.
pub fn from_hex(_hex: &str) -> Self {
todo!("Prefix::from_hex()")
}
}
impl std::fmt::Display for Prefix {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.bytes.to_hex_with_len(self.hex_len).fmt(f)
}
}