1 ! Copyright (c) 2008-2009 Doug Coleman.
2 ! See http://factorcode.org/license.txt for BSD license.
3 USING: combinators kernel locals math math.functions math.ranges
4 random sequences sets combinators.short-circuit math.bitwise
8 : >odd ( n -- int ) 0 set-bit ; foldable
10 : >even ( n -- int ) 0 clear-bit ; foldable
12 : next-even ( m -- n ) >even 2 + ;
14 : next-odd ( m -- n ) dup even? [ 1 + ] [ 2 + ] if ;
18 :: (miller-rabin) ( n trials -- ? )
20 n-1 factor-2s :> s :> r
24 2 n 2 - [a,b] random a!
29 2^ s * a swap n ^mod n - -1 =
36 : miller-rabin* ( n numtrials -- ? )
38 { [ dup 1 <= ] [ 3drop f ] }
39 { [ dup 2 = ] [ 3drop t ] }
40 { [ dup even? ] [ 3drop f ] }
41 [ drop (miller-rabin) ]
44 : miller-rabin ( n -- ? ) 10 miller-rabin* ;
46 ERROR: prime-range-error n ;
48 : next-prime ( n -- p )
49 dup 1 < [ prime-range-error ] when
53 next-odd dup miller-rabin [ next-prime ] unless
56 : random-bits* ( numbits -- n )
57 1 - [ random-bits ] keep set-bit ;
59 : random-prime ( numbits -- p )
60 random-bits* next-prime ;
62 ERROR: no-relative-prime n ;
66 : (find-relative-prime) ( n guess -- p )
67 over 1 <= [ over no-relative-prime ] when
68 dup 1 <= [ drop 3 ] when
69 2dup gcd nip 1 > [ 2 + (find-relative-prime) ] [ nip ] if ;
73 : find-relative-prime* ( n guess -- p )
74 #! find a prime relative to n with initial guess
75 >odd (find-relative-prime) ;
77 : find-relative-prime ( n -- p )
78 dup random find-relative-prime* ;
80 ERROR: too-few-primes ;
82 : unique-primes ( numbits n -- seq )
83 #! generate two primes
85 dup 5 < [ too-few-primes ] when
86 2dup [ random-prime ] curry replicate
87 dup all-unique? [ 2nip ] [ drop unique-primes ] if ;
89 ! Safe primes are of the form p = 2q + 1, p,q are prime
90 ! See http://en.wikipedia.org/wiki/Safe_prime
94 : safe-prime-candidate? ( n -- ? )
97 : next-safe-prime-candidate ( n -- candidate )
98 next-prime dup safe-prime-candidate?
99 [ next-safe-prime-candidate ] unless ;
103 : safe-prime? ( q -- ? )
105 [ 1 - 2 / dup integer? [ miller-rabin ] [ drop f ] if ]
109 : next-safe-prime ( n -- q )
110 next-safe-prime-candidate
111 dup safe-prime? [ next-safe-prime ] unless ;
113 : random-safe-prime ( numbits -- p )
114 random-bits* next-safe-prime ;