47. Register-type instructions

• 
      # arithmetic and logic
      add $t1, $t2, $t3
      or  $t1, $t2, $t3
      slt $t1, $t2, $t3
  
      # mult and div
      mult $t2, $t3
      div  $t2, $t3
  
      # move from/to
      mfhi $t1
      mflo $t1
  
      # jump register
      jr $ra