#!r6rs
(library (rsc3 u8 int)
(export int->u8l u8l->int)
(import (rnrs)
	(rsc3 collection lists))

(define (byte n i)
  (fxand (fxarithmetic-shift-right i n) #xFF))

(define (int->u8l n size)
  (map (lambda (b)
	 (byte b n))
       (iota (/ size 8) (- size 8) -8)))

;; >=?

(define (sign n b)
  (let ((z (expt 2 b)))
    (if (> n (/ z 2))
	(- n z)
	n)))

(define (u8l->int l signed?)
  (let ((n (length l)))
    (let ((u (fold
	      + 0
	      (map fxarithmetic-shift-left
		   l
		   (iota n (* (- n 1) 8) -8)))))
      (if signed?
	  (sign u (* n 8))
	  u))))

)