# Programming language shootout: fannkuch

### From Gambit wiki

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;; derived by Michael D. Adams from the O'Caml variant, by Christophe Papazian | ;; derived by Michael D. Adams from the O'Caml variant, by Christophe Papazian | ||

- | (declare (standard-bindings)(extended-bindings)(block)(not safe | + | (declare (standard-bindings)(extended-bindings)(block)(not safe)) |

(define (write-permutation perm) | (define (write-permutation perm) |

## Revision as of 13:59, 26 February 2008

This is a Gambit implementation of the fannkuch benchmark of the Computer Language Benchmarks Game.

## The program

#!gsi-script ;; The Computer Language Benchmarks Game ;; http://shootout.alioth.debian.org/ ;; Derived by Bradley Lucier from the Ikarus variant ;; derived by Michael D. Adams from the O'Caml variant, by Christophe Papazian (declare (standard-bindings)(extended-bindings)(block)(not safe)) (define (write-permutation perm) (for-each write (vector->list perm)) (newline)) ;; Find first value where r[i] != i ;; and increment (mod j+2) all values up to that (i.e. set them to j+1) ;; returning i+2 (define (choose-next r) (let loop ((i 0)) (if (eq? (vector-ref r i) i) (loop (fx+ 1 i)) (let loop ((j 0)) (if (eq? j i) (begin (vector-set! r j (fxremainder (fx+ 1 (vector-ref r j)) (fx+ j 2))) (fx+ j 2)) (begin (vector-set! r j (fx+ j 1)) (loop (fx+ j 1)))))))) ;; Count number of "pancake flips" it takes to get p[0]=1 ;; Does not side-effect p, uses s as a temporary ;; "Pancake flip" = Reverse first p[0]-1 elements (define (count-flips n p s) ;; Check if all p[i] != i+1 (define (check i) (or (eq? i n) (and (not (eq? (vector-ref p i) (fx+ i 1))) (check (fx+ i 1))))) ;; If all p[i] != i+1 (if (check 0) (begin ;; set all s[i] = p[i] (do ((i 0 (fx+ i 1))) ((eq? i n)) (vector-set! s i (vector-ref p i))) ;; keep reversing the first s[0]-1 values of s until s[0] = 1 ;; and return number of flippings (do ((flips 0 (fx+ flips 1)) (s0 (fx- (vector-ref s 0) 1) (fx- (vector-ref s 0) 1))) ((eq? s0 0) flips) ;; reverse the first s[0]-1 values of s (do ((i 0 (fx+ i 1)) (j s0 (fx- j 1))) ((fx>= i j)) (let ((tmp (vector-ref s i))) (vector-set! s i (vector-ref s j)) (vector-set! s j tmp))))) 0)) ;; Build a new permutation by "braiding": ;; For every i in [1..n-1]: ;; Shift each p[j<i] down by one ;; and put p[0] at p[i] (define (braid n p) ;; For every i in [1..n-1] (do ((i 1 (fx+ i 1))) ((eq? i n)) ;; Shift each p[j] down by one ;; and put p[0] at p[i] (let ((t (vector-ref p 0))) (do ((j 0 (fx+ j 1))) ((eq? j i)) (vector-set! p j (vector-ref p (fx+ j 1)))) (vector-set! p i t)))) (define (fannkuch n r p s m z) (let ((i (choose-next r))) (if (fx> i n) m (begin (if (fx> z 0) (write-permutation p)) (braid i p) (fannkuch n r p s (max m (count-flips n p s)) (fx- z 1)))))) (define (main . args) (let ((n (string->number (car args)))) (let ((r (make-vector n)) (p (make-vector n)) (s (make-vector n 0))) ;; Init r and p to [1,...,n] (do ((i 0 (fx+ 1 i))) ((eq? i n)) (vector-set! r i (fx+ i 1)) (vector-set! p i (fx+ i 1))) ;; No need to init s; it is only used as a temporary (let ((x (fannkuch n r p s 0 30))) (display "Pfannkuchen(")(display n)(display ") = ") (display x)(newline)))))

## Compiling

gsc fannkuch

## Running

gsi fannkuch n