爲什麼我的模擬器中按位操作返回0？

Question

所以，我有我的模擬器此代碼的字節轉換爲十六進制

byteToHex(opcode) { 
     var tempCode = (opcode).toString(16).toUpperCase() 
     var addln = 4 - tempCode.length 
     var pad ="" 
     for(var i = 0; i< addln; i++) { 
      pad = pad + "0" 
     } 
     var newCode = "0x"+ pad + tempCode 
     return newCode; 
} 

，我有這個代碼，執行按位運算得到一個操作碼，然後將其轉換使用。

this.opcode = (this.memory[this.pc] << 8) | this.memory[this.pc + 1] 
    console.log(this.memory) 
    console.log("before conversion", this.opcode) 
    this.opcode = this.byteToHex(this.opcode) 
    console.log(this.opcode) 
    //this just returns the first 'letter' of the opcode 
    switch (this.opcode & 0xF000)... 

這是控制檯輸出

Array [ 240, 144, 144, 144, 240, 32, 96, 32, 32, 112, 70 more… ] 
before conversion 0 
0x0000 

這意味着我得到了正確的操作碼，但我不知道如何解決它。 爲了更好地瞭解該項目：Github

Answer 1

下面是一些按預期運行的代碼。調試（不完整）代碼有點困難。由於StackOverflow的是關於具體問題和答案，我還沒有去打擾打摸出只是你要去哪裏錯了所需的猜測/偵探遊戲..

240D = 0XF0

144D = 0×90

[240，144]作爲一個單一的16位大端數處理被0xF090（英特爾的東西是小端，即至少顯著字節至上）

window.addEventListener('load', onDocLoaded, false); 
 

 
var memoryContents = [240, 144, 144, 144, 240, 32, 96, 32, 32, 112]; 
 

 
function getTwoLocationsBigEndian(indexOfFirst) 
 
{ 
 
\t var result = (memoryContents[indexOfFirst] << 8) | (memoryContents[indexOfFirst+1]); 
 
\t return result; 
 
} 
 

 
function getTwoLocationsLittleEndian(indexOfFirst) 
 
{ 
 
\t var result = (memoryContents[indexOfFirst+1] << 8) | (memoryContents[indexOfFirst]); 
 
\t return result; 
 
} 
 

 
function byteToHex(opcode) 
 
{ 
 
\t var tempCode = (opcode).toString(16).toUpperCase() 
 
\t var addln = 4 - tempCode.length 
 
\t var pad ="" 
 
\t for(var i = 0; i< addln; i++) 
 
\t { 
 
\t \t pad = pad + "0" 
 
\t } 
 
\t var newCode = "0x"+ pad + tempCode 
 
\t return newCode; 
 
} 
 

 
function onDocLoaded(evt) 
 
{ 
 
\t console.log("Memory contents: " + memoryContents); 
 
\t 
 
\t var opcode = getTwoLocationsBigEndian(0); 
 
\t console.log("***** BIG endian *****"); 
 
\t console.log("First 2 locs as a 16bit num (dec): " + opcode); 
 
\t console.log("First 2 locs as a 16bit num (hex): " + byteToHex(opcode)); 
 

 
\t opcode = getTwoLocationsLittleEndian(0); 
 
\t console.log("***** LITTLE endian *****"); 
 
\t console.log("First 2 locs as a 16bit num (dec): " + opcode); 
 
\t console.log("First 2 locs as a 16bit num (hex): " + byteToHex(opcode)); 
 
}