Created
October 15, 2013 09:32
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Miller-Rabin-Test
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; Prüft, ob eine Zahl eine Primzahl ist laut Miller-Rabin-Test. | |
; http://mathworld.wolfram.com/Rabin-MillerStrongPseudoprimeTest.html | |
; > Given an odd integer n [1], let n=2^rs+1 with s odd [2,3]. | |
; > Then choose a random integer a with 1<=a<=n-1 [4]. | |
; > If a^s=1 (mod n) [5] or a^(2^js)=-1 (mod n) [6] for some 0<=j<=r-1, then n passes the test. | |
(define (prim? n) | |
(cond | |
((< n 2) #f) | |
((>= n 2152302898747) (error "prim?" "Zu große Zahl" n)) ; '(2, 3) sind ausreichend für alle Zahlen < dieser | |
((memq n '(2 3 5 7 11)) #t) | |
((odd? n) ; [1] | |
(letrec* | |
( | |
(calcR | |
(lambda (n) | |
(if (odd? n) | |
0 | |
(+ 1 (calcR (/fx n 2))) | |
) | |
) | |
) | |
(r (calcR (- n 1))) ; [2] | |
(s (/ (- n 1) (expt 2 r))) ; [3] | |
; [6] a^(2js) = -1 mod n | |
(testPotenzen | |
(lambda (a r) | |
(cond ((< r 0) #f) | |
((= (- n 1) (pow a (* (expt 2 r) s) n)) #t) | |
(else (testPotenzen a (- r 1))) | |
) | |
) | |
) | |
; [5] a^s = 1 mod n | |
(testEinzeln | |
(lambda (a r) | |
;(print "einz " a " " r) | |
(if (= 1 (pow a s n)) | |
#t | |
(testPotenzen a r) | |
) | |
) | |
) | |
(test | |
(lambda (r werte) | |
;(print r " " werte) | |
(if (null? werte) | |
#t | |
(and (testEinzeln (car werte) r) (test r (cdr werte))) | |
) | |
) | |
) | |
) | |
(test r | |
'(2 3 5 7 11) ; [4] | |
) | |
) | |
) | |
(else #f) | |
) | |
) |
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