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        <h1>The Lua VM, on the Web</h1>
        <br>
        <p>This is an experiment in running <a href="http://www.lua.org/">Lua</a> on the web, by porting the Lua C implementation to JavaScript using <a href="http://emscripten.org">Emscripten</a>.</p>
        <br>
        <p><a href="#" class="btn btn-primary btn-large " onclick="run(); return false" id="the_button">Measure how fast your browser can run a VM in a VM &raquo;</a></p>
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          <h3>Individual Benchmark Results</h3>
            <table class="table table-striped table-bordered table-hover">
              <thead>
                <tr>
                  <th>Benchmark</th>
                  <th><div class="text-center">Result</div></th>
                  <th>Scale</th>
                  <th>What it measures</th>
                </tr>
              </thead>
              <tbody>
                <tr>
                  <td>binarytrees</td>
                  <td id="binarytrees-cell"><div id="binarytrees-output" class="text-center"></div></td>
                  <td>seconds (lower numbers are better)</td>
                  <td>GC performance</td>
                </tr>
                <tr>
                  <td>scimark</td>
                  <td id="scimark-cell"><div id="scimark-output" class="text-center"></div></td>
                  <td>MFLOPS (higher numbers are better)</td>
                  <td>numeric computation performance</td>
                </tr>
                <tr>
                  <td>startup</td>
                  <td id="startup-cell"><div id="startup-output" class="text-center"></div></td>
                  <td>seconds (lower numbers are better)</td>
                  <td>how long it takes the VM to be ready to run</td>
                </tr>
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            </table>
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          <h3>FAQ</h3>
          <h4>Are you really porting the entire Lua VM?</h4>
          <p>Yes: The entire Lua 5.2.2 codebase written in C is compiled to JavaScript here, including a full incremental GC and everything else.
             It fits in 200K of gzipped JavaScript.</p>
          <h4>How can a VM running in a VM be fast?</h4>
          <p>Lua is implemented in portable C. It is possible to run C compiled to JavaScript at speeds
             <a href="http://arstechnica.com/information-technology/2013/05/native-level-performance-on-the-web-a-brief-examination-of-asm-js/">approaching that of a native build</a> (using the <a href="http://asmjs.org/">asm.js</a> subset of
             JavaScript), which means that you can
             in principle run C code that happens to implement a VM at high speed as well. Of course this is theoretical until it is actually attempted - that is the point
             of this project.</p>
          <h4>What do the numbers here mean?</h4>
          <p>The individual benchmark results are reported in their native units, and have short descriptions in the table. The final combined score is more
             abstract, it is basically a normalized mean of the individual numbers, where higher numbers are better. The final score is intended to give a quick
             summarizing number for comparison purposes.</p>
          <h4>I got [X] on my machine, how does that compare to other results?</h4>
          <p>As one datapoint, my desktop (Firefox Nightly on 64-bit Linux) gets a score of 489. Comparing to a native build of Lua, the results are similar to
             other recent asm.js benchmarks (about 50% of native speed).</p>
          <p>If you want to compare the results to a native build on your machine, you can do so as follows:
             Grab <a href="http://www.lua.org/download.html">Lua 5.2.2</a> (the version compiled here to JavaScript), build it natively,
             and run the same benchmarks (<a href="binarytrees.lua">binarytrees</a>, <a href="scimark.lua">scimark</a>). To run them,
             execute <code>lua scimark.lua</code> and <code>lua binarytrees.lua 14.72</code> (don't forget the second argument in binarytrees).</p>
          <h4>What about <a href="http://luajit.org/">LuaJIT</a>?</h4>
          <p>This project ports Lua, not LuaJIT. LuaJIT is more challenging to port, because in addition to being a JIT, its interpreter is in
             optimized handwritten assembly. This is great for speed but makes things trickier when cross-compiling to a new platform.</p>
          <p>LuaJIT is significantly faster than Lua, so it is even more significantly faster than this port to the web. However, it's important
             to remember that even without LuaJIT, Lua is relatively fast compared to most other dynamic languages, like Python and Ruby, that
             are very useful in many cases even without blazing speed.</p>
          <h4>How do I build the Lua VM in JavaScript?</h4>
          <p>See how the Lua VM is built in the Emscripten benchmark suite, for example by <code>python tests/runner.py benchmark.test_lua_scimark</code>
             (the build here is copied from that, with the binarytrees.lua file embedded in it as well). You can also run <code>emmake make generic</code>
             in <code>lua/</code> in this repo, to generate the <a href="repl.html">REPL</a> build.</p>
          <h4>Can I use this to write web pages in Lua?</h4>
          <p>Work to connect Lua to the rest of the web environment is in progress, see the <a href="repl.html">REPL</a>
             and <a href="script_example.html">script example</a> pages.
          <h4>Can I help make that happen?</h4>
          <p>Yes! If you know Lua and want to help, <a href="https://github.com/kripken/lua.vm.js/issues">get in touch</a> :)
             We really need feedback and help from people that "get" Lua in order to do this properly.</p>
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    <script>
var ran = false;
function run() {
  if (ran) return;
  ran = true;

  var theButton = document.getElementById('the_button');
  theButton.innerHTML = 'Running benchmarks... (this can take a while)';
  theButton.classList.remove('btn-primary');
  theButton.classList.add('btn-warning');

  var jobs = [
    {
      benchmark: 'binarytrees',
      args: ['binarytrees.lua', '14.72'],
      calculate: function() {
        return this.msg.runtime/1000;
      },
      normalized: function() {
        return (20.308/this.calculate());
      },
    },
    {
      benchmark: 'scimark',
      args: ['scimark.lua'],
      calculate: function() {
        return /\nSciMark +([\d\.]+)/.exec(this.msg.output)[1]; 
      },
      normalized: function() {
        return (this.calculate()/3.19);
      },
    },
    { // do startup last so there is no network access, and can see previous
      benchmark: 'startup',
      args: ['nonexistent.lua'],
      calculate: function() {
        var startups = jobs.map(function(job) { return job.msg.startup });
        startups.sort(function(x, y) { return x - y });
        return startups[Math.floor((startups.length-1)/2)]/1000;
      },
      normalized: function() {
        return 0.10/Math.max(this.calculate(), 1/60); // resolution: 1 frame
      },
    }
  ];

  function finalCalculation() {
    // normalize based on experimental data
    var normalized = jobs.map(function(job) { return 100*job.normalized() });
    console.log('normalized values: ' + normalized);
    return Math.round(normalized.reduce(function(x, y) { return x + y }, 0));
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