efficient bytevector-slice for GNU Guile

bytevector-slice.scm

(use-modules (system foreign) (rnrs bytevector))

;; TODO: 
;; 1. (> hi (bytevector-length bv))
;; 2. (< lo 0) wrap reference
(define (%bytevector-slice bv lo hi)
  (and (< hi lo) (error %bytevector-slice "wrong range" lo hi))
  (let* ((ptr (bytevector->pointer bv))
         (addr (pointer-address ptr))
         (la (+ addr lo))
         (len (- hi lo)))
    (pointer->bytevector (make-pointer la) len)))
  
(define-syntax bytevector-slice
  (syntax-rules (:)
    ((_ bv lo : hi)
     (%bytevector-slice bv lo hi))
    ((_ bv lo :)
     (%bytevector-slice bv lo (bytevector-length bv)))
    ((_ bv : hi)
     (%bytevector-slice bv 0 hi))))

OK， this implementation is unsafe for GC, we have to define an obj with (make-object-property) in top-level to hold the original bytevector in case it was collected by GC.
But this means I have to lock the obj each time, no, no more lock as possible. I prefer copy.