title: What is the "relationship" between addi and subi?
body: <p>I'm supposed to answer this question. After some research it says that add and sub have the same opcode and differ only in the functional field. Is this the answer or something else?</p>
  
  <h2>Update</h2>
  
  <p>It's available in the Nios II CPU manual:</p>
  
  <pre><code>subi
  subtract immediate
  Operation: rB ← rA – σ (IMMED)
  Assembler Syntax: subi rB, rA, IMMED
  Example: subi r8, r8, 4
  Description: Sign-extends the immediate value IMMED to 32 bits, subtracts it from the value of rA and then
              stores the result in rB.
  Usage: The maximum allowed value of IMMED is 32768. The minimum allowed value is
  –32767.
  Pseudo-instruction:
  © March 2009
  subi is implemented as addi rB, rA, -IMMED
  </code></pre>