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Optimize algorithmic efficiency

tokio-rs/tokio
Based on 4 comments
Rust

Pay careful attention to operations inside loops and recursive functions to avoid unexpected algorithmic complexity. Be particularly vigilant about: 1. **Hidden O(n²) operations**: Avoid operations that iterate over entire collections inside loops, as they can degrade performance significantly.

Algorithms Rust

Reviewer Prompt

Pay careful attention to operations inside loops and recursive functions to avoid unexpected algorithmic complexity. Be particularly vigilant about:

  1. Hidden O(n²) operations: Avoid operations that iterate over entire collections inside loops, as they can degrade performance significantly.
// Poor performance: iterates through all buffers on each call
let n = bufs.iter().map(|b| b.len()).sum::<usize>().min(MAX_BUF);

// Better approach: avoid recomputing the total length repeatedly
let mut total = 0;
for buf in bufs {
    total += buf.len();
    if total >= MAX_BUF {
        total = MAX_BUF;
        break;
    }
}
  1. Prefer efficient bit operations: Use shifts, masks, and other bit-level operations instead of more expensive calculations when possible.
// Expensive calculation using power
let max_number = 2u64.saturating_pow((8 * length_field_len - 1) as u32);
max_number + (max_number - 1);

// More efficient using bit shift
let max_number = match 1.checked_shl(8 * length_field_len) {
    Some(shl) => shl - 1,
    None => u64::MAX,
}
  1. Reduce monomorphization bloat: Extract type-independent logic into separate functions to avoid code duplication across different type instantiations.
// Separate logic into non-generic helper function
pub(crate) fn spawn_child_with(
    cmd: &mut StdCommand,
    with: impl Fn(&mut StdCommand) -> io::Result<StdChild>,
) -> io::Result<SpawnedChild> {
    spawn_child(&mut with(cmd)?)
}

fn spawn_child(cmd: &mut StdChild) -> io::Result<SpawnedChild> {
    // Common implementation that won't be duplicated
}
  1. Use specialized methods: Many standard library types offer specialized methods that are more efficient than general-purpose approaches.
// Less efficient with multiple operations
if now > timeout.checked_add(Duration::from_millis(5)).unwrap_or_else(Instant::far_future) {
    // Handle case
}

// More efficient using a specialized method
if now.saturating_duration_since(timeout) > Duration::from_millis(5) {
    // Handle case
}

These optimizations matter most in hot code paths, libraries meant for wide adoption, or when handling large data structures.

4
Comments Analyzed
Rust
Primary Language
Algorithms
Category

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