1 files changed, 152 insertions, 0 deletions
diff --git a/vendor/gix-hash/src/prefix.rs b/vendor/gix-hash/src/prefix.rs
new file mode 100644
index 000000000..a8b55922e
--- /dev/null
+++ b/vendor/gix-hash/src/prefix.rs
@@ -0,0 +1,152 @@
+use std::{cmp::Ordering, convert::TryFrom};
+
+use crate::{oid, ObjectId, Prefix};
+
+/// The error returned by [Prefix::new()].
+#[derive(Debug, thiserror::Error)]
+#[allow(missing_docs)]
+pub enum Error {
+    #[error(
+        "The minimum hex length of a short object id is {}, got {hex_len}",
+        Prefix::MIN_HEX_LEN
+    )]
+    TooShort { hex_len: usize },
+    #[error("An object of kind {object_kind} cannot be larger than {} in hex, but {hex_len} was requested", object_kind.len_in_hex())]
+    TooLong { object_kind: crate::Kind, hex_len: usize },
+}
+
+///
+pub mod from_hex {
+    /// The error returned by [Prefix::from_hex][super::Prefix::from_hex()].
+    #[derive(Debug, Eq, PartialEq, thiserror::Error)]
+    #[allow(missing_docs)]
+    pub enum Error {
+        #[error(
+            "The minimum hex length of a short object id is {}, got {hex_len}",
+            super::Prefix::MIN_HEX_LEN
+        )]
+        TooShort { hex_len: usize },
+        #[error("An id cannot be larger than {} chars in hex, but {hex_len} was requested", crate::Kind::longest().len_in_hex())]
+        TooLong { hex_len: usize },
+        #[error("Invalid character {c} at position {index}")]
+        Invalid { c: char, index: usize },
+    }
+}
+
+impl Prefix {
+    /// The smallest allowed prefix length below which chances for collisions are too high even in small repositories.
+    pub const MIN_HEX_LEN: usize = 4;
+
+    /// 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 < Self::MIN_HEX_LEN {
+            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 `value`, e.g. `35e77c16` would yield a `Prefix` with `hex_len()` = 8.
+    pub fn from_hex(value: &str) -> Result<Self, from_hex::Error> {
+        use hex::FromHex;
+        let hex_len = value.len();
+
+        if hex_len > crate::Kind::longest().len_in_hex() {
+            return Err(from_hex::Error::TooLong { hex_len });
+        } else if hex_len < Self::MIN_HEX_LEN {
+            return Err(from_hex::Error::TooShort { hex_len });
+        };
+
+        let src = if value.len() % 2 == 0 {
+            Vec::from_hex(value)
+        } else {
+            let mut buf = [0u8; crate::Kind::longest().len_in_hex()];
+            buf[..value.len()].copy_from_slice(value.as_bytes());
+            buf[value.len()] = b'0';
+            Vec::from_hex(&buf[..value.len() + 1])
+        }
+        .map_err(|e| match e {
+            hex::FromHexError::InvalidHexCharacter { c, index } => from_hex::Error::Invalid { c, index },
+            hex::FromHexError::OddLength | hex::FromHexError::InvalidStringLength => panic!("This is already checked"),
+        })?;
+
+        let mut bytes = ObjectId::null(crate::Kind::from_hex_len(value.len()).expect("hex-len is already checked"));
+        let dst = bytes.as_mut_slice();
+        let copy_len = src.len();
+        dst[..copy_len].copy_from_slice(&src);
+
+        Ok(Prefix { bytes, hex_len })
+    }
+}
+
+/// Create an instance from the given hexadecimal prefix, e.g. `35e77c16` would yield a `Prefix`
+/// with `hex_len()` = 8.
+impl TryFrom<&str> for Prefix {
+    type Error = from_hex::Error;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        Prefix::from_hex(value)
+    }
+}
+
+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)
+    }
+}
+
+impl From<ObjectId> for Prefix {
+    fn from(oid: ObjectId) -> Self {
+        Prefix {
+            bytes: oid,
+            hex_len: oid.kind().len_in_hex(),
+        }
+    }
+}