perf: skip when matched len < 4

crates/compact-bytes/deno.json

@@ -1,6 +1,6 @@
 {
   "tasks": {
-    "flame": "CARGO_PROFILE_RELEASE_DEBUG=true cargo flamegraph --example permuted --root",
+    "flame": "CARGO_PROFILE_RELEASE_DEBUG=true cargo flamegraph --example permuted_slow --root",
     "bench": "cargo bench",
     "fuzz": "cargo +nightly fuzz run match",
     "test": "cargo nextest run && cargo test --doc"

crates/compact-bytes/examples/permuted.rs

@@ -4,7 +4,8 @@ pub fn main() {
     let data = include_str!("../benches/permuted.mht");
     // this simulate the situation in loro snapshot encoding,
     // where we first encode the state snapshot, then we look up the slices of the ops.
-    let mut bytes = CompactBytes::new();
+    let mut bytes = CompactBytes::with_capacity(data.len());
+    println!("{}", bytes.capacity());
     bytes.append(&data.as_bytes()[..data.len() / 2]);
     println!("{}", bytes.as_bytes().len()); // 114275
     bytes.alloc_advance(&data.as_bytes()[data.len() / 2..]);

crates/compact-bytes/examples/permuted_slow.rs

@@ -0,0 +1,11 @@
+use compact_bytes::CompactBytes;
+use criterion::black_box;
+
+pub fn main() {
+    let data = include_str!("../benches/permuted.mht");
+    for _ in 0..1000 {
+        let mut bytes = CompactBytes::new();
+        bytes.append(&black_box(data).as_bytes()[..data.len() / 2]);
+        bytes.alloc_advance(&black_box(&data.as_bytes()[data.len() / 2..]));
+    }
+}

crates/compact-bytes/src/lib.rs

@@ -44,7 +44,7 @@ impl CompactBytes {
         }
     }
 
-    /// cap must be a power of 2
+    /// cap will be adjusted to a power of 2
     pub fn with_capacity(cap: usize) -> Self {
         let cap = cap.max(1024).next_power_of_two();
         CompactBytes {
@@ -175,6 +175,10 @@ impl CompactBytes {
                         len += 1;
                     }
 
+                    if len < 4 {
+                        break;
+                    }
+
                     if len > max_len {
                         max_len = len;
                         ans_pos = pos;