zoukankan      html  css  js  c++  java
  • [WASM] Write to WebAssembly Memory from JavaScript

    We write a function that converts a string to lowercase in WebAssembly, demonstrating how to set the input string from JavaScript.

    WASM Fiddle: https://wasdk.github.io/WasmFiddle/?h1s69

    Demo Repo: https://github.com/guybedford/wasm-intro

     

    We want to create a funcrtion 'toLowerCase', which enable JS to write in Memory.

    To write data into WASM, we need to variables in C code, one is 'inStr' which get original input (for example 'Hello World'), another is 'outStr' which will transform to lower case string (for example: 'hello world').

    C code:

    void consoleLog (char* offset, int len);
    
    char inStr[20];
    char outStr[20];
    
    char* getInStrOffset () {
      return &inStr[0];
    }
    
    void toLowerCase() {
      for (int i = 0; i < 20; i++ ) {
        char c = inStr[i];
        if (c > 64 &&  c < 91) {
          c = c + 32;
        }
        outStr[i] = c;
      }
      consoleLog(&outStr[0], 20);
    }

    JS: Some code to get wasm instance.

    var wasmModule = new WebAssembly.Module(wasmCode);
    var wasmInstance = new WebAssembly.Instance(wasmModule, {
      env: {
        consoleLog (offset, len) {
          const strBuf = new Uint8Array(mem.buffer, offset, len);
          log(new TextDecoder().decode(strBuf));
        }
      }
    });
    const mem = wasmInstance.exports.memory;

    Now we need to write data from JS to WASM memory, the way to do it is just to put data into 'inStr':

    const mem = wasmInstance.exports.memory;
    
    function writeString (str, offset) {
      const strBuf = new TextEncoder().encode(str);
      const outBuf = new Uint8Array(mem.buffer, offset, strBuf.length);
      
    
    
    
          for (let i = 0; i < strBuf.length; i++) {
            outBuf[i] = strBuf[i];
          }
      }
    }
    
    writeString('Hello Web Assembly', wasmInstance.exports.getInStrOffset());

    Because what 'wasmInstance.exports.getInStrOffset()' return us is the first char address of 'inStr', then we use for loop to write data into 'inStr'.

    After writting the data, then we can call 'toLowerCase' to see the result:

    var wasmModule = new WebAssembly.Module(wasmCode);
    var wasmInstance = new WebAssembly.Instance(wasmModule, {
      env: {
        consoleLog (offset, len) {
          const strBuf = new Uint8Array(mem.buffer, offset, len);
          log(new TextDecoder().decode(strBuf));
        }
      }
    });
    const mem = wasmInstance.exports.memory;
    
    function writeString (str, offset) {
      const strBuf = new TextEncoder().encode(str);
      const outBuf = new Uint8Array(mem.buffer, offset, strBuf.length);
      
    
    
    
          for (let i = 0; i < strBuf.length; i++) {
            outBuf[i] = strBuf[i];
          }
      }
    }
    
    writeString('Hello Web Assembly', wasmInstance.exports.getInStrOffset());
    wasmInstance.exports.toLowerCase();
  • 相关阅读:
    从头来之【图解针对虚拟机iOS开发环境搭建】 (转)
    换工作?请记得8、18、48与72这四个密码(转)
    php
    linux上svn连接visual svn server时ssl鉴权失败,问题解决(转)
    javamail发送邮件的简单实例(转)
    稀疏矩阵
    Redis11种Web应用场景
    说说ShellExecuteEx
    怎样从host之外连接到docker container
    hadoop日志分析
  • 原文地址:https://www.cnblogs.com/Answer1215/p/7099324.html
Copyright © 2011-2022 走看看