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:
    排序算法<No.3>【桶排序】
    排序算法<No.2>【快速排序】
    排序算法<No.1> 【计数排序】
    排序问题思考(要求时间和空间复杂度尽可能的低)【Part 1】
    elasticsearch【cat API,系统数据】指令汇总
    netty研究【1】:编译源代码
    D3树状图给指定特性的边特别显示颜色
    zabbix3.0安装之图形界面显示异常【server】
    计算一维组合数的java实现
    zabbix3.0安装【server】
  • 原文地址:https://www.cnblogs.com/Answer1215/p/7099324.html
Copyright © 2011-2022 走看看