Rust Performance Speed-up Tricks

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These are my notes to optimize Rust performance. I generally check this after finishing coding to get some trivial performance gains.

• Loops

  let mut elements: Vec<u8> = vec![0; 1024];
  // Do something with the vector
  
  // SLOWER
  for i in 0..1024 {
      // This forces bounds checking for i every iteration
      println!("{}", elements[i]);
  }
  
  // FASTER
  // No bounds check here
  elements.iter().map(|e| {
      println!("{}", e);
  });
  

• Round-robin leaders

  let mut leader:usize = 0;
  const num_nodes:usize = 100;
  // ...
  
  // SLOWER
  leader = (leader+1)%num_nodes;
  
  // FASTER
  leader = if leader != num_nodes {
      // The common-case inside the true part to speed-up branch prediction
      leader + 1
  } else { 0 };
  

• Hash Maps

  // SLOWER
  use std::collections:HashMap;
  
  // FASTER
  // Use fnv = "*" or fnv = "0" in Cargo.toml
  use fnv::HashMap;