anchor.diff:  
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  -;;; Add imm to reg/mem, 16/32/64
  +;;; To a GPR or memory location (16/32/64) (destination), add an
  +;;; immediate value (16/32) (source), and store the result in the
  +;;; destination.
  +;;;
   ;;; Opcodes: 81
   ;;; Opcode extension 0
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  -;;; Add imm16 to reg/mem16
  -
  -;;; Add imm16 to reg16
  +;;; To a 16-bit GPR or memory location (destination), add an immediate
  +;;; 16-bit value (source), and store the result in the destination.
  +
  +;;; To a 16-bit GPR (destination), add an immediate 16-bit value
  +;;; (source), and store the result in the destination.
   (define-instruction "ADD"
     :modes (32 64)
     :operands ((gpr 16) (imm 16))
  
positive.code:   :opcode-extension 0
    :encoding (modrm imm))
  
  ;;; Add imm32 to mem32
  (define-instruction "ADD"
    :modes (32 64)
    :operands ((memory 32) (imm 32))
  
negative.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; To a 32-bit GPR or memory location (destination), add an immediate
  ;;; 32-bit sign-extended value (source), and store the result in the
  ;;; destination.
  
  ;;; To a 32-bit GPR (destination), add an immediate 32-bit
  ;;; sign-extended value (source), and store the result in the
  ;;; destination.
  (define-instruction "ADD"
    :modes (64)
    :operands ((gpr 64) (simm 32))
  