fast_formatting.rs

extern crate itoa;
extern crate smallvec;

macro_rules! print_time {
    ($start:expr, $end:expr) => (println!("time: {} ns", ($end - $start).subsec_nanos() as f32 / 1_000_000.0);)
}

// 189 ns
fn new_order_slow(stock: &str, price: i32, quantity: i32) -> String {
    format!("NEW {} {} {}", stock, price, quantity)
}

// 117 ns
fn new_order_fast(stock: &str, price: i32, quantity: i32) -> String {
    let mut s = Vec::<u8>::with_capacity(stock.len() + 6);
    s.extend_from_slice(b"NEW ");
    s.extend_from_slice(stock.as_bytes());
    s.push(b' ');
    itoa::write(&mut s, price).unwrap();
    s.push(b' ');
    itoa::write(&mut s, quantity).unwrap();
    unsafe { String::from_utf8_unchecked(s) }
}

// 78 ns
fn new_order_faster(stock: &str, price: i32, quantity: i32) -> String {
    use smallvec::SmallVec;
    let mut s = SmallVec::<[u8; 32]>::new();
    s.extend_from_slice(b"NEW ");
    s.extend_from_slice(stock.as_bytes());
    s.push(b' ');
    itoa::write(&mut s, price).unwrap();
    s.push(b' ');
    itoa::write(&mut s, quantity).unwrap();
    unsafe { String::from_utf8_unchecked(s.to_vec()) }
}

fn main() {

    {      
        println!("new_order_slow:");
        let mut last = String::new();
        let time_start = ::std::time::Instant::now();
        for i in 0..1_000_000 {
            last = new_order_slow("NVDA", i, i);
        }
        let time_end = ::std::time::Instant::now();
        println!("last: {}", last);
        print_time!(time_start, time_end);
    }

    {     
        println!("new_order_fast:");
        let mut last = String::new();
        let time_start = ::std::time::Instant::now();
        for i in 0..1_000_000 {
            last = new_order_fast("NVDA", i, i);
        }
        let time_end = ::std::time::Instant::now();
        println!("last: {}", last);
        print_time!(time_start, time_end);
    }

    {       
        println!("new_order_faster:");
        let mut last = String::new();
        let time_start = ::std::time::Instant::now();
        for i in 0..1_000_000 {
            last = new_order_faster("NVDA", i, i);
        }
        let time_end = ::std::time::Instant::now();
        println!("last: {}", last);
        print_time!(time_start, time_end);
    }
}