(import srfi-4
        chicken.foreign
        chicken.fixnum)

(: make-bit-vector (fixnum boolean -> u8vector))
(define (make-bit-vector size #!optional fill)
  (let* ((fill (if fill #b11111111 0))
         (len (fx/ (fx+ size 7) 8)))
    (make-u8vector len fill)))

(: bit-vector? (any -> boolean : u8vector))
(define bit-vector? u8vector?)

(: bit-vector-ref (u8vector fixnum -> boolean))
(define (bit-vector-ref vec i)
  ((foreign-lambda* bool ((u8vector vec) (size_t i))
     "size_t byte = i / 8;"
     "size_t off = i % 8;"
     "C_return (0 != (vec[byte] & (1<<off)));")
   vec
   i))

(: bit-vector-set! (u8vector fixnum boolean -> void))
(define (bit-vector-set! vec i x)
  ((foreign-lambda* void ((u8vector vec) (size_t i) (bool x))
     "size_t byte = i / 8;"
     "size_t off = i % 8;"
     "vec[byte] = x ? (vec[byte] | (1 << off)) : (vec[byte] & ~(1 << off));")
   vec
   i
   x))