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  1. ; morris counting
  2.  
  3. (define-syntax fold-of
  4.   (syntax-rules (range in is)
  5.     ((_ "z" f b e) (set! b (f b e)))
  6.     ((_ "z" f b e (v range fst pst stp) c ...)
  7.       (let* ((x fst) (p pst) (s stp)
  8.              (le? (if (positive? s) <= >=)))
  9.         (do ((v x (+ v s))) ((le? p v) b)
  10.           (fold-of "z" f b e c ...))))
  11.     ((_ "z" f b e (v range fst pst) c ...)
  12.       (let* ((x fst) (p pst) (s (if (< x p) 1 -1)))
  13.         (fold-of "z" f b e (v range x p s) c ...)))
  14.     ((_ "z" f b e (v range pst) c ...)
  15.       (fold-of "z" f b e (v range 0 pst) c ...))
  16.     ((_ "z" f b e (x in xs) c ...)
  17.       (do ((t xs (cdr t))) ((null? t) b)
  18.         (let ((x (car t)))
  19.           (fold-of "z" f b e c ...))))
  20.     ((_ "z" f b e (x is y) c ...)
  21.       (let ((x y)) (fold-of "z" f b e c ...)))
  22.     ((_ "z" f b e p? c ...)
  23.       (if p? (fold-of "z" f b e c ...)))
  24.     ((_ f i e c ...)
  25.       (let ((b i)) (fold-of "z" f b e c ...)))))
  26.  
  27. (define-syntax list-of (syntax-rules ()
  28.   ((_ arg ...) (reverse (fold-of
  29.     (lambda (d a) (cons a d)) '() arg ...)))))
  30.  
  31. (define rand #f)
  32. (define randint #f)
  33. (let ((two31 #x80000000) (a (make-vector 56 -1)) (fptr #f))
  34.   (define (mod-diff x y) (modulo (- x y) two31)) ; generic version
  35.   ; (define (mod-diff x y) (logand (- x y) #x7FFFFFFF)) ; fast version
  36.   (define (flip-cycle)
  37.     (do ((ii 1 (+ ii 1)) (jj 32 (+ jj 1))) ((< 55 jj))
  38.       (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
  39.     (do ((ii 25 (+ ii 1)) (jj 1 (+ jj 1))) ((< 55 ii))
  40.       (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
  41.     (set! fptr 54) (vector-ref a 55))
  42.   (define (init-rand seed)
  43.     (let* ((seed (mod-diff seed 0)) (prev seed) (next 1))
  44.       (vector-set! a 55 prev)
  45.       (do ((i 21 (modulo (+ i 21) 55))) ((zero? i))
  46.         (vector-set! a i next) (set! next (mod-diff prev next))
  47.         (set! seed (+ (quotient seed 2) (if (odd? seed) #x40000000 0)))
  48.         (set! next (mod-diff next seed)) (set! prev (vector-ref a i)))
  49.       (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle)))
  50.   (define (next-rand)
  51.     (if (negative? (vector-ref a fptr)) (flip-cycle)
  52.       (let ((next (vector-ref a fptr))) (set! fptr (- fptr 1)) next)))
  53.   (define (unif-rand m)
  54.     (let ((t (- two31 (modulo two31 m))))
  55.       (let loop ((r (next-rand)))
  56.         (if (<= t r) (loop (next-rand)) (modulo r m)))))
  57.   (init-rand 19380110) ; happy birthday donald e knuth
  58.   (set! rand (lambda seed
  59.     (cond ((null? seed) (/ (next-rand) two31))
  60.           ((eq? (car seed) 'get) (cons fptr (vector->list a)))
  61.           ((eq? (car seed) 'set) (set! fptr (caadr seed))
  62.                                  (set! a (list->vector (cdadr seed))))
  63.           (else (/ (init-rand (modulo (numerator
  64.                   (inexact->exact (car seed))) two31)) two31)))))
  65.   (set! randint (lambda args
  66.     (cond ((null? (cdr args))
  67.             (if (< (car args) two31) (unif-rand (car args))
  68.               (floor (* (next-rand) (car args)))))
  69.           ((< (car args) (cadr args))
  70.             (let ((span (- (cadr args) (car args))))
  71.               (+ (car args)
  72.                  (if (< span two31) (unif-rand span)
  73.                    (floor (* (next-rand) span))))))
  74.           (else (let ((span (- (car args) (cadr args))))
  75.                   (- (car args)
  76.                      (if (< span two31) (unif-rand span)
  77.                        (floor (* (next-rand) span))))))))))
  78.  
  79. (define (make-counter)
  80.   (let ((c 0))
  81.     (lambda ()
  82.       (when (zero? (randint (expt 2 c)))
  83.         (set! c (+ c 1)))
  84.       (- (expt 2 c) 1))))
  85.  
  86. (define (count n)
  87.   (let ((x (make-counter)))
  88.     (do ((n n (- n 1))) ((zero? n) (x)) (x))))
  89.  
  90. (display (list-of (count 25000) (x range 10)))
Success #stdin #stdout 3.08s 8036KB
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(16383 16383 8191 16383 32767 4095 65535 32767 16383 16383)
https://ideone.com/4CbPSh
language:
()
created:
9 years ago
visibility:
public

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