下一代Web基石 - WebAssembly

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0. 前言

WebAssembly/wasm 是一个由JavsScript进化来的,用于在浏览器内编写客户端脚本的底层的字节码格式。最初目的是支持编译C和C++语言。

1. 使用 WebAssembly

以C语言为例

比如C语言代码如下:

math.c

int square (int x) {
  return x * x;
}

首先使用emscripten将c代码编译为wasm,生成math.wasm文件

emcc math.c -Os -s WASM=1 -s SIDE_MODULE=1 -o math.wasm

然后在Web页面中加载math.wasm中的WebAssembly代码

function loadWebAssembly(filename, imports = {}) {
  return fetch(filename)
    .then(response => response.arrayBuffer())
    .then(buffer => WebAssembly.compile(buffer))
    .then(module => {
      imports.env = imports.env || {}
      Object.assign(imports.env, {
        memoryBase: 0,
        tableBase: 0,
        memory: new WebAssembly.Memory({ initial: 256, maximum: 256 }),
        table: new WebAssembly.Table({ initial: 0, maximum: 0, element: 'anyfunc' })
      })
      return new WebAssembly.Instance(module, imports)
    })
}

loadWebAssembly('math.wasm')
      .then(instance => {
        const square = instance.exports._square
        console.log('2^2 =', square(2))
        console.log('3^2 =', square(3))
        console.log('(2 + 5)^2 =', square(2 + 5))
})

更多WebAssembly Demo

https://github.com/Hanks10100/wasm-examples

3. 相关工具

安装 emscripten

http://kripken.github.io/emscripten-site/docs/getting_started/downloads.html

# Fetch the latest registry of available tools. ./emsdk update

# Download and install the latest SDK tools. ./emsdk install latest

# Make the “latest” SDK “active” for the current user. (writes ~/.emscripten file) ./emsdk activate latest

# Activate PATH and other environment variables in the current terminal source ./emsdk_env.sh

wasm2wast math.wasm -o math.wast

AdvancedTools

http://webassembly.org/getting-started/advanced-tools/

The WebAssembly Binary Toolkit

https://github.com/WebAssembly/wabt

OnlineDemo

https://cdn.rawgit.com/WebAssembly/wabt/013802ca01035365e2459c70f0508481393ac075/demo/wasm2wast/

WebAssembly语法

http://webassembly.org/docs/semantics/#type-parametric-operators

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