(sc-comment "depends on sys/types.h for ssize_t")

(sc-comment "! there may be a current segfaulting bug with small arrays of around size two.")

(define (quicksort less? swap array left right)
  (void (function-pointer uint8-t void* ssize-t ssize-t) (function-pointer void void* ssize-t ssize-t) void* ssize-t ssize-t)
  "a generic quicksort implementation that works with any array type.
   less should return true if the first argument is < than the second.
   swap should exchange the values of the two arguments it receives.
   quicksort(less, swap, array, 0, array-size - 1)"
  (if (<= right left) return)
  (define pivot ssize-t (+ left (/ (- right left) 2)))
  (define l ssize-t left)
  (define r ssize-t right)
  (while #t
    (while (less? array l pivot) (set+ l 1))
    (while (less? array pivot r) (set- r 1))
    (if (> l r) break)
    (cond ((= pivot l) (set pivot r)) ((= pivot r) (set pivot l)))
    (swap array l r)
    (set+ l 1)
    (set- r 1))
  (quicksort less? swap array left r)
  (quicksort less? swap array l right))