Drop faster-hex dependency

cli/src/commands/debug/tree.rs

@@ -47,7 +47,7 @@ pub fn cmd_debug_tree(
     let workspace_command = command.workspace_helper(ui)?;
     let tree = if let Some(tree_id_hex) = &args.id {
         let tree_id =
-            TreeId::try_from_hex(tree_id_hex).map_err(|_| user_error("Invalid tree id"))?;
+            TreeId::try_from_hex(tree_id_hex).ok_or_else(|| user_error("Invalid tree id"))?;
         let dir = if let Some(dir_str) = &args.dir {
             workspace_command.parse_file_path(dir_str)?
         } else {

lib/Cargo.toml

@@ -48,7 +48,6 @@ git2 = { workspace = true, optional = true }
 gix = { workspace = true, optional = true }
 gix-filter = { workspace = true, optional = true }
 glob = { workspace = true }
-faster-hex = { workspace = true }
 ignore = { workspace = true }
 indexmap = { workspace = true }
 itertools = { workspace = true }

lib/src/backend.rs

@@ -26,7 +26,6 @@ use thiserror::Error;
 
 use crate::content_hash::ContentHash;
 use crate::hex_util;
-use crate::hex_util::to_reverse_hex_digit;
 use crate::index::Index;
 use crate::merge::Merge;
 use crate::object_id::id_type;

lib/src/git_backend.rs

@@ -500,7 +500,7 @@ fn root_tree_from_header(git_commit: &CommitRef) -> Result<Option<MergedTreeId>,
         if *key == JJ_TREES_COMMIT_HEADER {
             let mut tree_ids = SmallVec::new();
             for hex in str::from_utf8(value.as_ref()).or(Err(()))?.split(' ') {
-                let tree_id = TreeId::try_from_hex(hex).or(Err(()))?;
+                let tree_id = TreeId::try_from_hex(hex).ok_or(())?;
                 if tree_id.as_bytes().len() != HASH_LENGTH {
                     return Err(());
                 }

lib/src/hex_util.rs

@@ -14,24 +14,20 @@
 
 #![allow(missing_docs)]
 
-pub fn to_reverse_hex_digit(b: u8) -> u8 {
-    let offset = match b {
-        b'0'..=b'9' => b - b'0',
-        b'A'..=b'F' => b - b'A' + 10,
-        b'a'..=b'f' => b - b'a' + 10,
-        b => return b,
-    };
-    b'z' - offset
+use std::iter;
+
+/// Converts a hexadecimal ASCII character to a 0-based index.
+fn hex_to_relative(b: u8) -> Option<u8> {
+    match b {
+        b'0'..=b'9' => Some(b - b'0'),
+        b'A'..=b'F' => Some(b - b'A' + 10),
+        b'a'..=b'f' => Some(b - b'a' + 10),
+        _ => None,
+    }
 }
 
 fn to_reverse_hex_digit_checked(b: u8) -> Option<u8> {
-    let value = match b {
-        b'0'..=b'9' => b - b'0',
-        b'A'..=b'F' => b - b'A' + 10,
-        b'a'..=b'f' => b - b'a' + 10,
-        _ => return None,
-    };
-    Some(b'z' - value)
+    Some(b'z' - hex_to_relative(b)?)
 }
 
 fn to_forward_hex_digit_checked(b: u8) -> Option<u8> {
@@ -61,11 +57,17 @@ pub fn to_reverse_hex(forward_hex: &str) -> Option<String> {
         .collect()
 }
 
-pub fn decode_hex_string(hex: &str) -> Option<Vec<u8>> {
-    let mut dst = vec![0; hex.len() / 2];
-    faster_hex::hex_decode(hex.as_bytes(), &mut dst)
-        .ok()
-        .map(|()| dst)
+pub fn decode_hex_string(src: &str) -> Option<Vec<u8>> {
+    if src.len() % 2 != 0 {
+        return None;
+    }
+    let mut dst = vec![0; src.len() / 2];
+    for (slot, bytes) in iter::zip(&mut dst, src.as_bytes().chunks_exact(2)) {
+        let a = hex_to_relative(bytes[0])? << 4;
+        let b = hex_to_relative(bytes[1])?;
+        *slot = a | b;
+    }
+    Some(dst)
 }
 
 /// Calculates common prefix length of two byte sequences. The length
@@ -82,23 +84,80 @@ pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {
 }
 
 pub fn encode_hex_string_reverse(src: &[u8]) -> String {
-    let mut buffer = vec![0; src.len() * 2];
-    faster_hex::hex_encode(src, &mut buffer).unwrap();
-    buffer
-        .iter_mut()
-        .for_each(|b| *b = to_reverse_hex_digit(*b));
+    let mut dst = vec![0; src.len() * 2];
+    for (&src, dst) in src.iter().zip(dst.chunks_exact_mut(2)) {
+        dst[0] = hex_lower_reverse((src >> 4) & 0xf);
+        dst[1] = hex_lower_reverse(src & 0xf);
+    }
+    String::from_utf8(dst).expect("hex_lower_reverse emits ascii character bytes")
+}
 
-    String::from_utf8(buffer).unwrap()
+fn hex_lower_reverse(byte: u8) -> u8 {
+    static TABLE: &[u8] = b"zyxwvutsrqponmlk";
+    TABLE[byte as usize]
 }
 
 pub fn encode_hex_string(src: &[u8]) -> String {
-    faster_hex::hex_string(src)
+    let mut dst = vec![0; src.len() * 2];
+    for (&src, dst) in src.iter().zip(dst.chunks_exact_mut(2)) {
+        dst[0] = hex_lower((src >> 4) & 0xf);
+        dst[1] = hex_lower(src & 0xf);
+    }
+    String::from_utf8(dst).expect("hex_lower emits ascii character bytes")
+}
+
+fn hex_lower(byte: u8) -> u8 {
+    static TABLE: &[u8] = b"0123456789abcdef";
+    TABLE[byte as usize]
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[test]
+    fn test_common_hex_len() {
+        assert_eq!(common_hex_len(b"", b""), 0);
+        assert_eq!(common_hex_len(b"abc", b"abc"), 6);
+
+        assert_eq!(common_hex_len(b"aaa", b"bbb"), 1);
+        assert_eq!(common_hex_len(b"aab", b"aac"), 5);
+    }
+
+    #[test]
+    fn test_encode_hex_string() {
+        assert_eq!(&encode_hex_string(b""), "");
+        assert_eq!(&encode_hex_string(b"012"), "303132");
+        assert_eq!(&encode_hex_string(b"0123"), "30313233");
+        assert_eq!(&encode_hex_string(b"abdz"), "6162647a");
+    }
+
+    #[test]
+    fn test_encode_hex_string_reverse() {
+        assert_eq!(&encode_hex_string_reverse(b""), "");
+        assert_eq!(&encode_hex_string_reverse(b"012"), "wzwywx");
+        assert_eq!(&encode_hex_string_reverse(b"0123"), "wzwywxww");
+        assert_eq!(&encode_hex_string_reverse(b"abdz"), "tytxtvsp");
+    }
+
+    #[test]
+    fn test_decode_hex_string() {
+        // Empty string
+        assert_eq!(decode_hex_string(""), Some(vec![]));
+
+        // Odd number of digits
+        assert_eq!(decode_hex_string("0"), None);
+
+        // Invalid digit
+        assert_eq!(decode_hex_string("g0"), None);
+        assert_eq!(decode_hex_string("0g"), None);
+
+        assert_eq!(
+            decode_hex_string("0123456789abcdefABCDEF"),
+            Some(b"\x01\x23\x45\x67\x89\xab\xcd\xef\xAB\xCD\xEF".to_vec())
+        );
+    }
+
     #[test]
     fn test_reverse_hex() {
         // Empty string

lib/src/object_id.rs

@@ -66,9 +66,8 @@ macro_rules! impl_id_type {
             }
 
             /// Parses the given hex string into an ObjectId.
-            pub fn try_from_hex(hex: &str) -> Result<Self, faster_hex::Error> {
-                let mut dst = vec![0; hex.len() / 2];
-                faster_hex::hex_decode(hex.as_bytes(), &mut dst).map(|()| Self(dst))
+            pub fn try_from_hex(hex: &str) -> Option<Self> {
+                $crate::hex_util::decode_hex_string(hex).map(Self)
             }
         }
 
@@ -96,7 +95,7 @@ macro_rules! impl_id_type {
             }
 
             fn hex(&self) -> String {
-                faster_hex::hex_string(&self.0)
+                $crate::hex_util::encode_hex_string(&self.0)
             }
         }
     };

lib/src/simple_op_store.rs

@@ -228,7 +228,7 @@ impl OpStore for SimpleOpStore {
                 if !name.starts_with(&hex_prefix) {
                     continue;
                 }
-                let Ok(id) = OperationId::try_from_hex(&name) else {
+                let Some(id) = OperationId::try_from_hex(&name) else {
                     continue; // Skip invalid hex
                 };
                 if matched.is_some() {
@@ -251,11 +251,11 @@ impl OpStore for SimpleOpStore {
     fn gc(&self, head_ids: &[OperationId], keep_newer: SystemTime) -> OpStoreResult<()> {
         let to_op_id = |entry: &fs::DirEntry| -> Option<OperationId> {
             let name = entry.file_name().into_string().ok()?;
-            OperationId::try_from_hex(&name).ok()
+            OperationId::try_from_hex(&name)
         };
         let to_view_id = |entry: &fs::DirEntry| -> Option<ViewId> {
             let name = entry.file_name().into_string().ok()?;
-            ViewId::try_from_hex(&name).ok()
+            ViewId::try_from_hex(&name)
         };
         let remove_file_if_not_new = |entry: &fs::DirEntry| -> Result<(), PathError> {
             let path = entry.path();