anchor.diff:              (let #+x86 ((rax sb-vm::eax-tn)
                           (rcx sb-vm::ecx-tn)
                           (rdi sb-vm::edi-tn))
  +                 #-x86 ()
                 #+x86
                 (progn
                   (unless (sb-vm::location= fill-word rax)
  
positive.code:                                  &key
                                     (dst-scale +fixnum-zero-mask+1+) (dst-offset 0)
                                     (src-scale +fixnum-zero-mask+1+) (src-offset 0))
             (let ((memcpy-fun ',%memcpy-name))
               `(,memcpy-fun ,dst ,dst-index ,src ,src-index ,n-words
                             ,dst-scale ,dst-offset
                             ,src-scale ,src-offset)))))))
  
  
  (define-fast-memcpy :memcpy-name fast-memcpy/4 :type (unsigned-byte 32) :size :dword)
  
negative.code:             (let #+x86 ((rcx sb-vm::ecx-tn)
                          (rsi sb-vm::esi-tn)
                          (rdi sb-vm::edi-tn))
                   #-x86 ()
                #+x86
                (progn
                  (unless (sb-vm::location= n-words rcx)
  