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<!doctype html>
<html lang="en">
<head>
<title>WebAssembly and Emscripten</title>
<meta name="viewport" content="width=device-width" />
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<meta charset="utf-8">
</head>
<body>
<div class="slide titlepage" tabindex="-1"
style="background-image: url('images/cpp-in-the-web.png');
background-position: center;
background-repeat: no-repeat;
background-size: 70%;
background-color: rgba(255, 255, 255, 0.85);
background-blend-mode: overlay;">
<p></p>
<p><span class="title">WebAssembly and Emscripten</span></p>
<p><span class="author">Sebastiano Tronto</span></p>
<p><span class="event">ALTEN Advanced Software Evening</span></p>
</div>
<div class="slide" tabindex="-1">
<h1>Your browser runs code</h1>
<div class="columns">
<div style="text-align: center;">
<input id="aInput" size=10 style="font-size: 24px;">
<br>
+
<br>
<input id="bInput" size=10 style="font-size: 24px;">
<br>
<button id="resultButton" style="font-size: 24px;">=</button>
<br>
<span id="resultText" style="font-size: 30px;"></span>
</div>
<pre><code class="language-javascript"
style="border: 0.2vw solid; font-size: 2.2vw;">
var aInput = document.getElementById("aInput");
var bInput = document.getElementById("bInput");
var button = document.getElementById("resultButton");
var resultText = document.getElementById("resultText");
button.addEventListener("click", () => {
var a = Number(aInput.value);
var b = Number(bInput.value);
resultText.innerText = a + b;
});
</code></pre></div>
</div>
<div class="slide" tabindex="-1">
<h1>WebAssembly</h1>
<div class="columns">
<a href="https://webassembly.org/">
<img src="images/wasm-logo.png" style="width: 80%;">
</a>
<div>
<p style="text-align: center;">
WASM first appeared in 2017 as a more performant language for the browser.
</p>
<p style="text-align: center;">
It runs in a VM and can interact with JavaScript, but not with the DOM.
</p>
</div>
</div>
</div>
<div class="slide" tabindex="-1">
<h1>WebAssembly - code example</h1>
<div class="columns">
<pre><code class="language-wasm"
style="border: 0.2vw solid; font-size: 2.1vw;">
(func (param i64) (result i64)
local.get 0
i64.eqz
if (result i64)
i64.const 1
else
local.get 0
local.get 0
i64.const 1
i64.sub
call 0
i64.mul
end)
</code></pre>
<div></div>
</div>
</div>
<div class="slide" tabindex="-1">
<h1>WebAssembly - code example</h1>
<div class="columns">
<pre><code class="language-wasm"
style="border: 0.2vw solid; font-size: 2.1vw;">
(func (param i64) (result i64)
local.get 0
i64.eqz
if (result i64)
i64.const 1
else
local.get 0
local.get 0
i64.const 1
i64.sub
call 0
i64.mul
end)
</code></pre>
<div>
Same thing in Python:
<pre><code class="language-python"
style="border: 0.2vw solid; font-size: 2.1vw;">
def f(n):
if n == 0:
return 1
else
return n * f(n-1)
</code></pre>
</div>
</div>
</div>
<div class="slide" tabindex="-1">
<h1>Emscripten</h1>
<a href="https://emscripten.org/index.html">
<img src="images/emscripten-logo-full.png">
</a>
<p style="text-align: center;">
<strong>
"Emscripten is a complete compiler toolchain to WebAssembly, using LLVM,
with a special focus on speed, size, and the Web platform."
</strong>
</p>
</div>
<div class="slide" tabindex="-1">
<h1>Hello, world!</h1>
<div class="columns">
<ol>
<li>Write an Hello World program in C or C++</li>
<li>Compile with <pre>emcc -o index.html hello.c</pre></li>
<li>Run a web server and
<a href="./examples/1-hello-world">open a browser</a>!</li>
</ol>
<img src="images/meme.png" style="width: 35%;">
</div>
</div>
<div class="slide" tabindex="-1">
<h1>Writing a library</h1>
<i>Thanks Emscripten, we'll write our own HTML!</i>
<div class="columns">
<img src="./images/sum.jpg" style="width: 70%;">
<div>
<ul>
<li><strong>Goal:</strong>
write a library with a function to sum two numbers,
and use it in a simple web page</li>
<li>See <a href=./examples/2-sum>examples/2-sum</a></li>
<li>Some extra options are needed:</li>
</ul>
<pre><code class="language-shell">
emcc -sEXPORTED_FUNCTIONS=_sum \
-sMODULARIZE \
-sEXPORT_NAME=SumLibrary \
-o sum_library.mjs \
sum_library.c
</code></pre>
</div>
</div>
</div>
<div class="slide" tabindex="-1">
<h1>Exercise: count prime numbers</h1>
<div class="columns">
<ul>
<li>Write a web app that takes a single integer n as input
and prints <strong>the number of prime numbers less than n</strong> when
the user presses a button.</li>
<li>Solution: <a href=./examples/3-primes>examples/3-primes</a></li>
</ul>
<img src="./images/meme2.jpg" style="width: 70%;">
</div>
</div>
<div class="slide" tabindex="-1">
<h1>Performance benchmark</h1>
<table id="bench">
<tr>
<th></th>
<th>Firefox <br>WASM (-O3)</th><th>Firefox <br>JS</th>
<th>Chromium <br>WASM (-O3)</th><th>Chromium <br>JS</th>
</tr>
<tr>
<td>1e7 Primes (iterative)</td>
<td>4.5s</td><td>4.4s</td>
<td>4.7s</td><td>4.6s</td>
<tr>
<tr>
<td>1e7 Primes (sieve)</td>
<td>0.76s</td><td>0.82s</td>
<td>0.92s</td><td>0.80s</td>
<tr>
<tr>
<td>Matrix multiplication</td>
<td>0.81s</td><td>5.3s</td>
<td>1.5s</td><td>4.6s</td>
<tr>
</table>
<img src="./images/fast.jpg" style="width: 30%; margin: auto;">
</div>
<div class="slide" tabindex="-1">
<h1>More exercises</h1>
<p>See <a href="https://github.com/sebastianotronto/emscripten-tutorial">
github.com/sebastianotronto/emscripten-tutorial</a></p>
<div class="columns">
<ul>
<li><strong>Fix UI freezing:</strong> very large numbers in example 3
can block the UI. Can you fix this?</li>
<li><strong>More faster:</strong> use multi-threading
(<a href="https://en.wikipedia.org/wiki/Pthreads">pthreads</a> or
<a href="https://en.cppreference.com/w/cpp/thread/thread.html">std::thread</a>) to make our examples faster. Watch out for
<a href="https://spectreattack.com/">Spectre</a>!</li>
<li><strong>Show progress:</strong> using callback functions, make our
long-running examples show their progress in the web page.</li>
</ul>
<img src="./images/pencil.jpg" style="width: 60%; margin: auto;">
</div>
</div>
<div class="slide titlepage" tabindex="-1"
style="background-image: url('images/beer.jpg');
background-position: center;
background-repeat: no-repeat;
background-size: 80%;
background-color: rgba(255, 255, 255, 0.65);
background-blend-mode: overlay;">
<p></p>
<p><span class="title">Drinks!</span></p>
<p></p>
</div>
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if (keysNext.includes(e.key) && i+1 < slides.length) {
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|
