perf(tree): parse entry mode into number instead of comparing it to b…

…yte strings (#67)

git-object/src/tree/ref_iter.rs

@@ -80,6 +80,23 @@ impl<'a> TryFrom<&'a [u8]> for tree::EntryMode {
  }
 }
 
+impl TryFrom<u32> for tree::EntryMode {
+ type Error = u32;
+
+ fn try_from(mode: u32) -> Result<Self, Self::Error> {
+ Ok(match mode {
+ 0o40000 => tree::EntryMode::Tree,
+ 0o100644 => tree::EntryMode::Blob,
+ 0o100755 => tree::EntryMode::BlobExecutable,
+ 0o120000 => tree::EntryMode::Link,
+ 0o160000 => tree::EntryMode::Commit,
+ 0o100664 => tree::EntryMode::Blob, // rare and found in the linux kernel
+ 0o100640 => tree::EntryMode::Blob, // rare and found in the Rust repo
+ _ => return Err(mode),
+ })
+ }
+}
+
 mod decode {
  use std::convert::TryFrom;
 
@@ -99,15 +116,22 @@ mod decode {
  const NULL: &[u8] = b"\0";
 
  pub fn fast_entry(i: &[u8]) -> Option<(&[u8], EntryRef<'_>)> {
- let (mode, i) = i.split_at(i.find_byte(b' ')?);
+ let mut mode = 0u32;
+ let mut spacer_pos = 1;
+ for b in i.iter().take_while(|b| **b != b' ') {
+ if *b < b'0' || *b > b'7' {
+ return None;
+ }
+ mode = (mode << 3) + (b - b'0') as u32;
+ spacer_pos += 1;
+ }
+ let (_, i) = i.split_at(spacer_pos);
  let mode = tree::EntryMode::try_from(mode).ok()?;
- let i = &i[1..];
  let (filename, i) = i.split_at(i.find_byte(0)?);
  let i = &i[1..];
  const HASH_LEN_FIXME: usize = 20; // TODO: know actual /desired length or we may overshoot
  let (oid, i) = match i.len() {
  len if len < HASH_LEN_FIXME => return None,
- HASH_LEN_FIXME => (i, &[] as &[u8]),
  _ => i.split_at(20),
  };
  Some((