Flutter: convert issue (2)

main.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:crypto/crypto.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

  MyHomePage({Key key, this.title}) :
  super(key: key);

  @override
  MyHomePageState createState() {
    return new MyHomePageState();
  }
}

class MyHomePageState extends State<MyHomePage> {
  Stopwatch sw;
  int ms;
  int totalms;
  int count;


  @override
  void initState(){
    sw = Stopwatch();
    count = 0;
    totalms = 0;
    convert();
    super.initState();
  }

  void refresh(int i){
    print("refresh with: $i");
    setState(() {
      count = i;
    });
  }

  int convert(){
    List<int> U_i = [121, -8, 43, -70, 22, -31, -22, -60, -32, 44, 74, -81, 22, -19, 25, 47, -40, 88, 22, -64, -64, -41, 45, 73, -46, 19, 13, 87, -53, 57, -75, -116, 0, 0, 0, 1];
    int c = 50;
//    int c = 10000;
    List<int> password = [66, 97, 115, 115, 103, 64, 49, 57, 49, 57];
    Hmac hmac = Hmac(sha256, password);

    int l = 32;
//    int l = 5;
    for (int i = 1; i <= l; i++) {
      sw.start();
      for (int i = 0; i < c; i++) {
        U_i = hmac.convert(U_i).bytes;
      }
      ms = sw.elapsedMilliseconds;
      print('took ${ms} ms');
      totalms+=ms;
      refresh(i);
    }

    return U_i[0];
  }

  @override
  Widget build(BuildContext context) {


    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(count.toString()),
            Text(totalms.toString())
          ],
        ),
      ),
    );
  }
}