如何将 ArrayBuffer 的特定范围设置为随机数？

Question

我想将 16 字节 ArrayBuffer 的前 29 位设置为 [0, 2^28 - 1] 范围内的随机值，与系统字节顺序。

以下是我的尝试，但这（可能）设置了 all 32 位。我能做些什么？有没有办法做类似 randomNumberHere & 0x1FFFFFFF?

的事情

let buffer = new ArrayBuffer(16);
let view = new Uint32Array(buffer.slice(0, 4));
window.crypto.getRandomValues(view);

Answer 1

您可以在 ArrayBuffer 上使用按位操作数

buffer & 0xE0000000 ^ window.crypto.getRandomValues(view) & 0x1FFFFFFF

Answer 2

可以使用位运算

function PrintBuffer(buffer){
  
  var dataview = new DataView(buffer, 0);
  var dataSize = buffer.byteLength;
  var index =0;
  var str =""
  while( index <dataSize){
      str +="_" + dataview.getUint8(index).toString(2).padStart(8, '0');
      index++;
  }  
    //console.log(str);
  return str;
}



let buffer = new ArrayBuffer(16);
// Copy the values into the array starting at index 3
//const uint8 = new Uint8Array(buffer);
//uint8.set([1, 2, 3,4,5,6,7,8,9,10,11,12,13,14,15,16], 0);
let view = new Uint32Array(buffer.slice(0, 4));
window.crypto.getRandomValues(view);

// Before Update
$('.root').prepend("<strong>Result</strong>.");
console.log(":Before");

console.log("Orignal ArrayBuffer : " + PrintBuffer(buffer));
console.log("Spliced Encrypted ArrayBuffer : " +PrintBuffer(view.buffer));
/* **************************************************
 *   Bits udate
 ***************************************************/
             const NumberOfBits = 29 // This bit count 
             const octet =8
         const quotient =  (NumberOfBits - NumberOfBits % octet) / octet;
         const remainder = NumberOfBits % octet;
         
        var encryptedView = new DataView(view.buffer, 0);
        var orignalBufferView = new DataView(buffer);
        
        for(var i=0;i<quotient;i++){
          this.orignalBufferView.setInt8(i, encryptedView.getUint8(i));
        }
        
        if(remainder>0){
           // remainder=2;
           var oldVal = orignalBufferView.getUint8(quotient);
           var newVal = encryptedView.getUint8(quotient);
       
           const maskForOldValue = new Uint8Array([1,3,7,15,31,63,127,255]);
           const maskForNewValue = new Uint8Array([128,192,224,240,248,252,254]);
           
           oldVal = oldVal & maskForOldValue[7-remainder];
          newVal = newVal & maskForNewValue[remainder-1];

          orignalBufferView.setInt8(quotient, oldVal | newVal);
     
          
        }
    
/***************************************************
*
*************************************************-*/
//After update
console.log(":After");
console.log("Modified ArrayBuffer : " + PrintBuffer(buffer));

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="root">
</div>

Answer 3

这是我所做的。更长一点，但也更直接。

import crypto from 'crypto';

let buffer = new ArrayBuffer(16);

let randomValue = crypto.randomInt(0, (1 << 29) - 1);
let view = new DataView(buffer);
view.setUint32(0, randomValue);

如何将 ArrayBuffer 的特定范围设置为随机数？

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