RustよりJSが早かった時のソースコード

index.js

var addon = require('../native');

const factorial = (x) => {
  let res = x;
  let done = false;

  while (!done) {
      x = x - 1;

      res = res * x;

      if (x < 2) {
          done = true;
      };
  };

  return res
}



console.time('rust')

for (let i = 1; i <= 10000; i++) {
  addon.factorial(i)
}

console.timeEnd('rust')

console.time('js')

for (let i = 1; i <= 10000; i++) {
  factorial(i)
}

console.timeEnd('js')

lib.rs

#[macro_use]
extern crate neon;

use neon::prelude::*;

fn factorial(mut cx: FunctionContext) -> JsResult<JsNumber> {
    let mut x = cx.argument::<JsNumber>(0)?.value();
    let mut res = x;
    let mut done = false;

    while !done {
        x = x - 1.0;

        res = res * x;

        if x < 2.0 {
            done = true;
        };
    };

    Ok(cx.number(res))
}

register_module!(mut cx, {
    cx.export_function("factorial", factorial)
});