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(define-module (starling ring-buffer)
#:use-module (srfi srfi-9)
#:export (make-ring-buffer
ring-buffer
ring-buffer-length
ring-buffer-put!
ring-buffer-get!
ring-buffer-ref
ring-buffer-clear!))
(define-record-type <ring-buffer>
(%make-ring-buffer vector length head tail)
ring-buffer?
(vector ring-buffer-vector)
(length ring-buffer-length set-ring-buffer-length!)
(head ring-buffer-head set-ring-buffer-head!)
(tail ring-buffer-tail set-ring-buffer-tail!))
(define (make-ring-buffer size)
(%make-ring-buffer (make-vector size #f) 0 0 0))
(define (ring-buffer-empty? ring)
(zero? (ring-buffer-length ring)))
(define (ring-buffer-put! ring x)
(let* ((head (ring-buffer-head ring))
(tail (ring-buffer-tail ring))
(l (ring-buffer-length ring))
(v (ring-buffer-vector ring))
(vl (vector-length v)))
(vector-set! v tail x)
(set-ring-buffer-length! ring (min (+ l 1) vl))
(when (and (> l 0) (= head tail))
(set-ring-buffer-head! ring (modulo (+ head 1) vl)))
(set-ring-buffer-tail! ring (modulo (+ tail 1) vl))))
(define (ring-buffer-get! ring)
(if (ring-buffer-empty? ring)
(error "ring buffer empty" ring)
(let* ((head (ring-buffer-head ring))
(v (ring-buffer-vector ring))
(result (vector-ref v head)))
(vector-set! v head #f)
(set-ring-buffer-head! ring (modulo (+ head 1) (vector-length v)))
(set-ring-buffer-length! ring (- (ring-buffer-length ring) 1))
result)))
(define (ring-buffer-ref ring i)
(let ((l (ring-buffer-length ring))
(v (ring-buffer-vector ring)))
(if (>= i l)
(error "ring buffer index out of bounds" i)
(vector-ref v (modulo (+ (ring-buffer-head ring) i)
(vector-length v))))))
(define (ring-buffer-clear! ring)
(let ((l (ring-buffer-length ring))
(v (ring-buffer-vector ring)))
(set-ring-buffer-head! ring 0)
(set-ring-buffer-tail! ring 0)
(let loop ((i 0))
(when (< i l)
(vector-set! v i #f)
(loop (+ i 1))))))
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