Created
March 12, 2013 13:32
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Find (prime) factors.
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#!/usr/bin/perl | |
use strict; | |
use warnings; | |
use utf8; | |
use Math::BigInt lib=>'GMP'; | |
use Math::Primality qw(is_prime); | |
my $n = Math::BigInt->new('280671392065546467397265294532969672241810318954163887187279320454220348884327'); | |
my $original_n = $n->copy(); | |
#my $n = Math::BigInt->new('481362815814826159'); | |
#my $n = Math::BigInt->new('225'); | |
# is_prime で返ってくる値から文字列に | |
my @factor_kind = ( 'composite', '(possibly) prime', 'prime' ); | |
# 疑似乱数列を作成する関数 | |
# f(x) = x^2+1 mod n | |
sub f { | |
my $x = shift; | |
return $x->copy()->bpow( 2 )->binc()->bmod( $n ); | |
} | |
# 先に n が素数かどうかを確認する | |
if ( my $is_prime = is_prime( $n ) ) { | |
print "$n is $factor_kind[$is_prime].\n"; | |
exit 0; | |
} | |
# 得られた因数のリスト | |
my @factors = (); | |
# Pollard's rho algorithm | |
while (1) { | |
print "n = $n\n"; | |
my $x = Math::BigInt->new('2'); | |
my $y = Math::BigInt->new('2'); | |
my $d = Math::BigInt->new('1'); | |
while ( $d == 1 ) { | |
$x = f($x);#print "$x\n"; | |
$y = f(f($y));#print "$y\n"; | |
$d = Math::BigInt::bgcd( (Math::BigInt->babs( $x - $y ), $n) ); | |
if ( $d == $n ) { | |
last; | |
} | |
} | |
if ( $d == $n ) { | |
# 疑似乱数列が循環したら、残りが素数かどうかを確認しつつ終了する | |
my $is_prime = is_prime( $n ); | |
print "rest ($factor_kind[$is_prime]) $n\n"; | |
push @factors, $n; | |
last; | |
} | |
# 因数が見つかった | |
push @factors, $d; | |
my $is_prime = is_prime( $d ); | |
print "factor ($factor_kind[$is_prime]) $d\n"; | |
$n->bdiv( $d ); | |
# 因数で割った残りが素数(または疑似素数)であれば、終了 | |
if ( $is_prime = is_prime( $n ) ) { | |
print "factor ($factor_kind[$is_prime]) $n\n"; | |
push @factors, $n; | |
last; | |
} | |
} | |
# 結果を表示 | |
# 結果は、表面積が最小のパターンを探すのに利用する | |
print "$original_n = \n"; | |
print join ( 'x', @factors ), "\n"; | |
exit 0; | |
1; |
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