title: x86 find out operand size of instruction given only the hex machine code?
body: <p>For example, given a hex:  <code>83 E4 F0</code></p>
  
  <p>By looking at the intel developer's manual, I can figure out that <code>83</code> means <code>and</code> and <code>FO</code> means the <code>-16</code>. Looking at <code>E4</code>, I can decode that the source/destination register is either SP or ESP.</p>
  
  <p>Therefore, I can conclude that the hex means either <code>and $-16, %ESP</code> or <code>and $-16, %SP</code>. However, in the manual, both of those are listed as <code>83 /4 ib</code>.</p>
  
  <p>How can I differentiate between those two?</p>