anchor.diff:    (sys.lap-x86:shr64 :rax 8)
     (sys.lap-x86:shr64 :rdx 8)
     ;; TODO: Full division...
  +  (sys.lap-x86:cmp64 :rdx 1)
  +  (sys.lap-x86:jne not-implemented)
  +  (sys.lap-x86:cmp64 :rax 2)
  +  (sys.lap-x86:je 128-bit-number)
     (sys.lap-x86:cmp64 :rax 1)
  -  (sys.lap-x86:jne not-implemented)
  -  (sys.lap-x86:cmp64 :rdx 1)
     (sys.lap-x86:jne not-implemented)
     ;; 64-bit divide.
     (sys.lap-x86:mov64 :rax (:r8 #.(+ (- +tag-array-like+) 8)))
     (sys.lap-x86:mov64 :rcx (:r9 #.(+ (- +tag-array-like+) 8)))
     (sys.lap-x86:cqo)
     ;; Quotient in RAX, remainder in RDX.
  +  do-divide
     (sys.lap-x86:idiv64 :rcx)
     (sys.lap-x86:push :rdx)
     ;; Attempt to convert quotient to a fixnum.
  
positive.code:   ;; Pick the longest length.
    (sys.lap-x86:mov64 :rcx :rax)
    (sys.lap-x86:cmp64 :rax :rdx)
    (sys.lap-x86:cmov64g :rcx :rdx)
    (sys.lap-x86:xor64 :rbx :rbx) ; offset
    (sys.lap-x86:xor64 :r11 :r11) ; CF save register.
    (sys.lap-x86:shl64 :rax 3)
  
negative.code:   ;; Pick the longest length.
    (sys.lap-x86:mov64 :rcx :rax)
    (sys.lap-x86:cmp64 :rax :rdx)
    (sys.lap-x86:cmov64ng :rcx :rdx)
    (sys.lap-x86:xor64 :rbx :rbx) ; offset
    (sys.lap-x86:xor64 :r10 :r10) ; CF save register.
    (sys.lap-x86:shl64 :rax 3)
  